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  • Articles  (1,196)
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  • Articles: DFG German National Licenses  (1,196)
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  • 1
    Electronic Resource
    Electronic Resource
    Unsteady convection and convection-diffusion problems via direct overlapping domain decomposition methods (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Numerical Methods for Partial Differential Equations 14 (1998), S. 387-406 
    Details
    ISSN: 0749-159X
    Keywords: Mathematics and Statistics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Notes: In solving unsteady problems,domain decomposition methods may be used either for iterative preconditioning each global implicit time-step or directly (noniteratively) within a blockwise implicit time-stepping procedure, in the latter case, the inner boundary values for the subproblems are generated by explicit time-extrapolation. The overlapping variants of this method have been proved to be efficient tools for solving parabolic and first-order hyperbolic problems on modern parallel computers, because they require global communication only once per time-step. The mechanism making this possible is the exponential decay in space of the time-discrete Green's function. We investigate several model problems of convection and convection-diffusion. Favorable optimal and far-reaching estimates of the overlap required have been established in the case of exemplary standard upwind finite-difference schemes. In particular, it has been shown that the overlap for the convection-diffusion problem is the additive function of overlaps for the corresponding convection and diffusion problem to be considered independently. These results have been confirmed with several numerical test examples. © 1998 John Wiley & Sons, Inc. Numer Methods Partial Differential Eq 14: 387-406, 1998
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  • 2
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    Electronic Resource
    A first-second order splitting method for a third-order partial differential equation (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Numerical Methods for Partial Differential Equations 14 (1998), S. 89-96 
    Details
    ISSN: 0749-159X
    Keywords: finite element method ; third-order differential equation ; Mathematics and Statistics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Notes: A splitting of a third order partial differential equation into a first-order and a second-order one is proposed as the basis for a mixed finite element method to approximate its solution. A time-continuous numerical method is described and error estimates for its solution are demonstrated. Finally, a full discretization is described based on backward Euler finite differences in time, and error estimates for the resulting approximation are established. © 1998 John Wiley & Sons, Inc. Numer Methods Partial Differential Eq 14: 89-96, 1998
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  • 3
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    Galerkin discontinuous approximation of the transport equation and viscoelastic fluid flow on quadrilaterals (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Numerical Methods for Partial Differential Equations 14 (1998), S. 97-114 
    Details
    ISSN: 0749-159X
    Keywords: non-Newtonian fluids ; finite elements ; error estimates ; Mathematics and Statistics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Notes: Numerical simulation of industrial processes involving viscoelastic liquids is often based on finite element methods on quadrilateral meshes. However, numerical analysis of these methods has so far been limited to triangular meshes. In this work, we consider quadrilateral meshes. We first study the approximation of the transport equation by a Galerkin discontinuous method and prove an O(hk+1/2) error estimates for the Qk finite element. Then we study a differential model for viscoelastic flow with unknowns u the velocity, p the pressure, and σ the viscoelastic part of the extra-stress tensor. The approximations are ((Q1)2 transforms of) Qk+1 continuous for u, Qk discontinuous for σ, and Pk discontinuous for p, with k ≥ 1. Upwinding for σ is obtained by the Galerkin discontinuous method. We show that an error estimate of order O(hk+1/2) is valid in the energy norm for the three unknowns. © 1998 John Wiley & Sons, Inc. Numer Methods Partial Differential Eq 14: 97-114, 1998
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  • 4
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    Stabilized spectral element approximation for the Navier-Stokes equations (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Numerical Methods for Partial Differential Equations 14 (1998), S. 115-141 
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    ISSN: 0749-159X
    Keywords: Navier-Stokes equations ; spectral elements ; stabilization techniques ; Mathematics and Statistics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Notes: The conforming spectral element methods are applied to solve the linearized Navier-Stokes equations by the help of stabilization techniques like those applied for finite elements. The stability and convergence analysis is carried out and essential numerical results are presented demonstrating the high accuracy of the method as well as its robustness. © 1998 John Wiley & Sons, Inc. Numer Methods Partial Differential Eq 14: 115-141, 1998
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  • 5
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    Spectral approximation in the numerical stability study of nondivergent viscous flows on a sphere (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Numerical Methods for Partial Differential Equations 14 (1998), S. 143-157 
    Details
    ISSN: 0749-159X
    Keywords: Normal mode stability ; spectral approximation ; Mathematics and Statistics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Notes: The accuracy of calculating the normal modes in the numerical linear stability study of two-dimensional nondivergent viscous flows on a rotating sphere is analyzed. Discrete spectral problems are obtained by truncating Fourier's series of the spherical harmonics for both the basic flow and the disturbances to spherical polynomials of degrees K and N, respectively. The spectral theory for the closed operators [1], and embedding theorems for the Hilbert and Banach spaces of smooth functions on a sphere are used to estimate the rate of convergence of the eigenvalues and eigenvectors. It is shown that the convergence takes place if the basic state is sufficiently smooth, and the truncation numbers K and N of Fourier's series for the basic flow and disturbances tend to infinity keeping the ratio N/K fixed. The convergence rate increases with the smoothness of the basic flow and with the power s of the Laplace operator in the vorticity equation diffusion term. © 1998 John Wiley & Sons, Inc. Numer Methods Partial Differential Eq 14:143-157, 1998
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  • 6
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    A second-order ADI scheme for three-dimensional parabolic differential equations (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Numerical Methods for Partial Differential Equations 14 (1998), S. 159-168 
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    ISSN: 0749-159X
    Keywords: ADI scheme ; parabolic differential equation ; stability ; Mathematics and Statistics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Notes: A second-order unconditionally stable ADI scheme has been developed for solving three-dimensional parabolic equations. This scheme reduces three-dimensional problems to a succession of one-dimensional problems. Further, the scheme is suitable for simulating fast transient phenomena. Numerical examples show that the scheme gives an accurate solution for the parabolic equation and converges rapidly to the steady state solution. © 1998 John Wiley & Sons, Inc. Numer Methods Partial Differential Eq 14:159-168, 1998
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  • 7
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    A two-stage least-squares finite element method for the stress-pressure-displacement elasticity equations (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Numerical Methods for Partial Differential Equations 14 (1998), S. 297-315 
    Details
    ISSN: 0749-159X
    Keywords: elasticity equations ; least-squares ; finite elements ; error estimates ; Mathematics and Statistics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Notes: A new stress-pressure-displacement formulation for the planar elasticity equations is proposed by introducing the auxiliary variables, stresses, and pressure. The resulting first-order system involves a nonnegative parameter that measures the material compressibility for the elastic body. A two-stage least-squares finite element procedure is introduced for approximating the solution to this system with appropriate boundary conditions. It is shown that the two-stage least-squares scheme is stable and, with respect to the order of approximation for smooth exact solutions, the rates of convergence of the approximations for all the unknowns are optimal both in the H1-norm and in the L2-norm. Numerical experiments with various values of the parameter are examined, which demonstrate the theoretical estimates. Among other things, computational results indicate that the behavior of convergence is uniform in the nonnegative parameter. © 1998 John Wiley & Sons, Inc. Numer Methods Partial Differential Eq 14: 297-315, 1998
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  • 8
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    Monotone iterations for numerical solutions of reaction-diffusion-convection equations with time delay (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Numerical Methods for Partial Differential Equations 14 (1998), S. 339-351 
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    ISSN: 0749-159X
    Keywords: monotone iteration ; finite difference equation ; reaction-diffusion-convection ; time delay ; upper and lower solutions ; Mathematics and Statistics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Notes: In this article we use the monotone method for the computation of numerical solutions of a nonlinear reaction-diffusion-convection problem with time delay. Three monotone iteration processes for a suitably formulated finite-difference system of the problem are presented. It is shown that the sequence of iteration from each of these iterative schemes converges from either above or below to a unique solution of the finite-difference system without any monotone condition on the nonlinear reaction function. An analytical comparison result among the three processes of iterations is given. Also given is the application of the iterative schemes to some model problems in population dynamics, including numerical results of a model problem with known analytical solution. © 1998 John Wiley & Sons, Inc. Numer Methods Partial Differential Eq 14: 339-351, 1998
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  • 9
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    A numerical method for the first-order wave equation with discontinuous initial data (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Numerical Methods for Partial Differential Equations 14 (1998), S. 353-365 
    Details
    ISSN: 0749-159X
    Keywords: Euler equations ; contact discontinuity ; finite difference schemes ; dispersion ; first-order wave equation ; Mathematics and Statistics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Notes: We introduce a method, constructed such that numerical solutions of the wave equation are well behaved when the solutions also contain discontinuities. The wave equation serves as a model problem for the Euler equations when the solution contains a contact discontinuity. Numerical computations of linear equations and the Euler equations in one and two dimensions are presented. © 1998 John Wiley & Sons, Inc. Numer Methods Partial Differential Eq 14: 353-365, 1998
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  • 10
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    Superconvergence in the projected-shear plate-bending finite element method (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Numerical Methods for Partial Differential Equations 14 (1998), S. 367-386 
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    ISSN: 0749-159X
    Keywords: finite element methods ; superconvergence ; the Reissner-Mindlin plate ; Mathematics and Statistics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Notes: A projected-shear finite element method for periodic Reissner-Mindlin plate model are analyzed for rectangular meshes. A projection operator is applied to the shear stress term in the bilinear form. Optimal error estimates in the L2-norm, the H1-norm, and the energy norm for both displacement and rotations are established and gradient superconvergence along the Gauss lines is justified in some weak senses. All the convergence and superconvergence results are uniform with respect to the thickness parameter t. © 1998 John Wiley & Sons, Inc. Numer Methods Partial Differential Eq 14: 367-386, 1998
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  • 11
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    Global and domain-decomposed mixed methods for the solution of Maxwell's equations with application to magnetotellurics (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Numerical Methods for Partial Differential Equations 14 (1998), S. 407-437 
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    ISSN: 0749-159X
    Keywords: Maxwell's equations ; magnetotellurics ; domain decomposition ; Mathematics and Statistics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Notes: A collection of global and domain decomposition mixed finite element schemes for the approximate solution of the harmonic Maxwell's equations on a bounded domain with absorbing boundary conditions at the artificial boundaries are presented. The numerical procedures allow us to solve efficiently the direct problem in magnetotellurics consisting of determining the electromagnetic scattered field in a two-dimensional earth model of arbitrary conductivity properties. Convergence results for the numerical procedures are derived. © 1998 John Wiley & Sons, Inc. Numer Methods Partial Differential Eq 14: 407-437, 1998
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  • 12
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    The coupling of boundary integral and finite element methods for the nonstationary exterior flow (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Numerical Methods for Partial Differential Equations 14 (1998), S. 549-565 
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    ISSN: 0749-159X
    Keywords: boundary integral ; finite element ; Navier-Stokes equations ; Mathematics and Statistics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Notes: In this article, we represent a new numerical method for solving the nonstationary Navier-Stokes equations in an unbounded domain. The technique consists of coupling the boundary integral and the finite element method. The variational formulation and the well-posedness of the coupling method are obtained. The convergence and optimal error estimates for the approximate solution are provided. © 1998 John Wiley & Sons, Inc. Numer Methods Partial Differential Eq 14: 549-565, 1998
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  • 13
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    Numerical analysis of finite element methods for miscible displacements in porous media (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Numerical Methods for Partial Differential Equations 14 (1998), S. 519-548 
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    ISSN: 0749-159X
    Keywords: miscible displacements ; finite elements ; error estimates ; Mathematics and Statistics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Notes: Finite element methods are used to solve a coupled system of nonlinear partial differential equations, which models incompressible miscible displacement in porous media. Through a backward finite difference discretization in time, we define a sequentially implicit time-stepping algorithm that uncouples the system at each time-step. The Galerkin method is employed to approximate the pressure, and accurate velocity approximations are calculated via a post-processing technique involving the conservation of mass and Darcy's law. A stabilized finite element (SUPG) method is applied to the convection-diffusion equation delivering stable and accurate solutions. Error estimates with quasi-optimal rates of convergence are derived under suitable regularity hypotheses. Numerical results are presented confirming the predicted rates of convergence for the post-processing technique and illustrating the performance of the proposed methodology when applied to miscible displacements with adverse mobility ratios. © 1998 John Wiley & Sons, Inc. Numer Methods Partial Differential Eq 14: 519-548, 1998
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  • 14
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    Finite differences on triangular grids (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Numerical Methods for Partial Differential Equations 14 (1998), S. 567-579 
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    ISSN: 0749-159X
    Keywords: finite difference ; finite element ; triangular grid ; Mathematics and Statistics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Notes: We define a finite differences method for triangular grids and we show how to link it to a finite element method. From this new point of view we then analyze properties of the solution and convergence. © 1998 John Wiley & Sons, Inc. Numer Methods Partial Differential Eq 14: 567-579, 1998
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  • 15
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    Symbolic derivation of finite difference approximations for the three-dimensional Poisson equation (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Numerical Methods for Partial Differential Equations 14 (1998), S. 593-606 
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    ISSN: 0749-159X
    Keywords: finite difference approximations ; Poisson equation ; symbolic computation ; Mathematica ; three-dimensions ; Mathematics and Statistics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Notes: A symbolic procedure for deriving various finite difference approximations for the three-dimensional Poisson equation is described. Based on the software package Mathematica, we utilize for the formulation local solutions of the differential equation and obtain the standard second-order scheme (7-point), three fourth-order finite difference schemes (15-point, 19-point, 21-point), and one sixth-order scheme (27-point). The symbolic method is simple and can be used to obtain the finite difference approximations for other partial differential equations. © 1998 John Wiley & Sons, Inc. Numer Methods Partial Differential Eq 14: 593-606, 1998
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  • 16
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    Applications of a space decomposition method to linear and nonlinear elliptic problems (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Numerical Methods for Partial Differential Equations 14 (1998), S. 717-737 
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    ISSN: 0749-159X
    Keywords: parallel ; domain decomposition ; nonlinear ; elliptic equation ; space decomposition ; Mathematics and Statistics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Notes: This work presents some space decomposition algorithms for a convex minimization problem. The algorithms has linear rate of convergence and the rate of convergence depends only on four constants. The space decomposition could be a multigrid or domain decomposition method. We explain the detailed procedure to implement our algorithms for a two-level overlapping domain decomposition method and estimate the needed constants. Numerical tests are reported for linear as well as nonlinear elliptic problems. © 1998 John Wiley & Sons, Inc. Numer Methods Partial Differential Eq 14: 717-737, 1998
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  • 17
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    A second-order splitting combined with orthogonal cubic spline collocation method for the Rosenau equation (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Numerical Methods for Partial Differential Equations 14 (1998), S. 695-716 
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    ISSN: 0749-159X
    Keywords: Rosenau equation ; orthogonal spline collocation method ; differential algebraic equations (DAEs) ; implicit Runge-Kutta methods ; decay estimates ; BBM (Benjamin-Bona-Mahony) equation ; BBMB (Benjamin-Bona-Mahony-Burgers) equation ; Mathematics and Statistics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Notes: A second-order splitting method is applied to a KdV-like Rosenau equation in one space variable. Then an orthogonal cubic spline collocation procedure is employed to approximate the resulting system. This semidiscrete method yields a system of differential algebraic equations (DAEs) of index 1. Error estimates in L2 and L∞ norms have been obtained for the semidiscrete approximations. For the temporal discretization, the time integrator RADAU5 is used for the resulting system. Some numerical experiments have been conducted to validate the theoretical results and to confirm the qualitative behaviors of the Rosenau equation. Finally, orthogonal cubic spline collocation method is directly applied to BBM (Benjamin-Bona-Mahony) and BBMB (Benjamin-Bona-Mahony-Burgers) equations and the well-known decay estimates are demonstrated for the computed solution. © 1998 John Wiley & Sons, Inc. Numer Methods Partial Differential Eq 14: 695-716, 1998
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  • 18
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    On the numerical integration of multi-dimensional, initial boundary value problems for the Euler equations in quasi-linear form (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Numerical Methods for Partial Differential Equations 14 (1998), S. 781-814 
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    ISSN: 0749-159X
    Keywords: hyperbolic problems ; IBVP ; multi-dimensional ; nonorthogonal mesh ; quasi-linear form ; Mathematics and Statistics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Notes: A matricial formalism to solve multi-dimensional initial boundary values problems for hyperbolic equations written in quasi-linear based on the λ scheme approach is presented. The derivation is carried out for nonorthogonal, moving systems of curvilinear coordinates. A uniform treatment of the integration at the boundaries, when the boundary conditions can be expressed in terms of combinations of time or space derivatives of the primitive variables, is also presented. The methodology is validated against a two-dimensional test case, the supercritical flow through the Hobson cascade n.2, and in three-dimensional test cases such as the supersonic flow about a sphere and the flow through a plug nozzle. © 1998 John Wiley & Sons, Inc. Numer Methods Partial Differential Eq 14: 781-814, 1998
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  • 19
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    A finite difference scheme for traveling wave solutions to Burgers equation (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Numerical Methods for Partial Differential Equations 14 (1998), S. 815-820 
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    ISSN: 0749-159X
    Keywords: Burgers equation ; nonstandard finite difference schemes ; traveling waves ; exact solutions ; Mathematics and Statistics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Notes: We construct a finite difference scheme for the ordinary differential equation describing the traveling wave solutions to the Burgers equation. This difference equation has the property that its solution can be calculated. Our procedure for determining this solution follows closely the analysis used to obtain the traveling wave solutions to the original ordinary differential equation. The finite difference scheme follows directly from application of the nonstandard rules proposed by Mickens. © 1998 John Wiley & Sons, Inc. Numer Methods Partial Differential Eq 14: 815-820, 1998
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  • 20
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    A model of a homogenized cavity corresponding to a multinozzle droplet generator for continuous ink-jet printers (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Numerical Methods for Partial Differential Equations 14 (1998), S. 821-842 
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    ISSN: 0749-159X
    Keywords: homogenization ; asymptotic analysis ; ink-jet printer ; droplet generator ; Mathematics and Statistics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Notes: We modelize the behavior of a vibrating fluid cavity. Small nozzles are uniformly distributed in one direction on a side of the cavity. By means of asymptotic expansion in powers of the smallest dimension of the cavity, including boundary layer terms, we get the convergence of the solution of the three-dimensional problem, as well as the convergence of the solution of the “homogenized” three-dimensional problem towards the solution of the same two-dimensional problem. Numerical experiments have been carried out in order to illustrate the previous theoretical results. © 1998 John Wiley & Sons, Inc. Numer Methods Partial Differential Eq 14: 821-842, 1998
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  • 21
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    Approximation to a parabolic system modeling the thermoelastic contacts of two rods (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Numerical Methods for Partial Differential Equations 14 (1998), S. 1-25 
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    ISSN: 0749-159X
    Keywords: Finite difference ; thermoelastic contact ; nonlinear parabolic system ; Mathematics and Statistics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Notes: In this article, we study a sequence of finite difference approximate solutions to a parabolic system, which models two dissimilar rods that may come into contact as a result of thermoelastic expansion. We construct the approximate solutions based on a set of finite difference schemes to the system, and we will prove that the approximate solutions converge strongly to the exact solutions. Moreover, we obtain and prove rigorously the error bound, which measures the difference between the exact solutions and approximate solutions in a reasonable norm. © 1998 John Wiley & Sons, Inc. Numer Methods Partial Differential Eq 14: 1-25, 1998
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    A space decomposition method for parabolic equations (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Numerical Methods for Partial Differential Equations 14 (1998), S. 27-46 
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    ISSN: 0749-159X
    Keywords: Parallel ; domain decomposition ; parabolic equation ; space decomposition ; Mathematics and Statistics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Notes: A convergence proof is given for an abstract parabolic equation using general space decomposition techniques. The space decomposition technique may be a domain decomposition method, a multilevel method, or a multigrid method. It is shown that if the Euler or Crank-Nicolson scheme is used for the parabolic equation, then by suitably choosing the space decomposition, only O(| log τ |) steps of iteration at each time level are needed, where τ is the time-step size. Applications to overlapping domain decomposition and to a two-level method are given for a second-order parabolic equation. The analysis shows that only a one-element overlap is needed. Discussions about iterative and noniterative methods for parabolic equations are presented. A method that combines the two approaches and utilizes some of the good properties of the two approaches is tested numerically. © 1998 John Wiley & Sons, Inc. Numer Methods Partial Differential Eq 14: 27-46, 1998
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    Preconditioners for the p-version of the Galerkin method for a coupled finite element/boundary element system (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Numerical Methods for Partial Differential Equations 14 (1998), S. 47-61 
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    ISSN: 0749-159X
    Keywords: p-version finite element method ; boundary element method ; interface problem ; preconditioning ; domain decomposition ; additive Schwarz method ; Mathematics and Statistics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Notes: We propose and analyze efficient preconditioners for solving systems of equations arising from the p-version for the finite element/boundary element coupling. The first preconditioner amounts to a block Jacobi method, whereas the second one is partly given by diagonal scaling. We use the generalized minimum residual method for the solution of the linear system. For our first preconditioner, the number of iterations of the GMRES necessary to obtain a given accuracy grows like log2 p, where p is the polynomial degree of the ansatz functions. The second preconditioner, which is more easily implemented, leads to a number of iterations that behave like p log3 p. Computational results are presented to support this theory. © 1998 John Wiley & Sons, Inc. Numer Methods Partial Differential Eq 14: 47-61, 1998
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  • 24
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    Gauss point mass lumping schemes for Maxwell's equations (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Numerical Methods for Partial Differential Equations 14 (1998), S. 63-88 
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    ISSN: 0749-159X
    Keywords: Maxwell equations ; edge finite elements ; mass lumping ; Mathematics and Statistics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Notes: Finite element and finite difference methods for approximating the Maxwell system propagate numerical waves with slightly incorrect velocities, and this results in phase error in the computed solution. Indeed this error limits the type of problem that can be solved, because phase error accumulates during the computation and eventually destroys the solution. Here we propose a family of mass-lumped finite element schemes using edge elements. We emphasize in particular linear elements that are equivalent to the standard Yee FDTD scheme, and cubic elements that have superior phase accuracy. We prove theorems that allow us to perform a dispersion analysis of the two common families of edge elements on rectilinear grids. A result of this analysis is to provide some justification for the choice of the particular family we use. We also provide a limited selection of numerical results that show the efficiency of our scheme. © 1998 John Wiley & Sons, Inc. Numer Methods Partial Differential Eq 14: 63-88, 1998
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    Superconvergent recovery of gradients of piecewise linear finite element approximations on non-uniform mesh partitions (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Numerical Methods for Partial Differential Equations 14 (1998), S. 169-192 
    Details
    ISSN: 0749-159X
    Keywords: finite element space ; (1 + α˜)-regular mesh partition ; recovered gradient ; superconvergence ; Mathematics and Statistics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Notes: We propose the use of an averaging scheme, which recovers gradients from piecewise linear finite element approximations on the (1 + α˜) - regular triangular elements to gradients of the weak solution of a second-order elliptic boundary value problem in the 2-dimensional space. The recovered gradients, from mid-points of element edges, are superconvergent estimates of the true gradients. This work is an extension of Levine [Levine, IMA J. Numer. Anal. 5, 407 (1985)] and follows some of the ideas therein. © 1998 John Wiley & Sons, Inc. Numer Methods Partial Differential Eq 14:169-192, 1998
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    Finite volume methods on Voronoi meshes (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Numerical Methods for Partial Differential Equations 14 (1998), S. 193-212 
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    ISSN: 0749-159X
    Keywords: Cell-centered finite differences ; upwind approximations ; error estimates ; Mathematics and Statistics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Notes: Two cell-centered finite difference schemes on Voronoi meshes are derived and investigated. Stability and error estimates in a discrete H1-norm for both symmetric and nonsymmetric problems, including convection dominated, are proven. The theoretical results are illustrated with several numerical experiments. © 1998 John Wiley & Sons, Inc. Numer Methods Partial Differential Eq 14:193-212, 1998
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    Convergence analysis of a finite volume method via a new nonconforming finite element method (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Numerical Methods for Partial Differential Equations 14 (1998), S. 213-231 
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    ISSN: 0749-159X
    Keywords: cell-centered finite volume method ; convergence ; finite element method ; Mathematics and Statistics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Notes: The article is devoted to the study of convergence properties of a Finite Volume Method (FVM) using Voronoi boxes for discretization. The approach is based on the construction of a new nonconforming Finite Element Method (FEM), such that the system of linear equations coincides completely with that for the FVM. Thus, by proving convergence properties of the FEM, we obtain similar ones of the FVM. In this article, the investigations are restricted to the Poisson equation. © 1998 John Wiley & Sons, Inc. Numer Methods Partial Differential Eq 14:213-231, 1998
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    A numerical method for problems in infinite strips with irregularities extending to infinity (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Numerical Methods for Partial Differential Equations 14 (1998), S. 233-249 
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    ISSN: 0749-159X
    Keywords: Infinite domain ; semi-infinite strip ; Dirichlet-to-Neumann ; Finite element ; variable coefficients ; nonlinear elliptic PDEs ; Mathematics and Statistics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Notes: The Dirichlet-to-Neumann (DtN) Finite Element Method is a combined analytic-numerical method for boundary value problems in infinite domains. The use of this method is usually based on the assumption that, in the infinite domain D exterior to the finite computational domain, the governing differential equations are sufficiently simple. In particular, in D it is generally assumed that the equations are linear, homogeneous, and have constant coefficients. In this article, an extension of the DtN method is proposed, which can be applied to elliptic problems with “irregularities” in the exterior domain D, such as (a) inhomogeneities, (b) variable coefficients, and (c) nonlinearities. This method is based on iterative “regularization” of the problem in D, and on the efficient treatment of infinite-domain integrals. Semi-infinite strip problems are used for illustrating the method. Convergence of the iterative process is analyzed both theoretically and numerically. Nonuniformity difficulties and a way to overcome them are discussed. © 1998 John Wiley & Sons, Inc. Numer Methods Partial Differential Eq 14:233-249, 1998
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    Moving finite element methods by use of space-time elements: I. Scalar problems (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Numerical Methods for Partial Differential Equations 14 (1998), S. 251-262 
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    ISSN: 0749-159X
    Keywords: Moving finite element ; discontinuous Galerkin ; space-time orientation ; Mathematics and Statistics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Notes: This article deals with moving finite element methods by use of the time-discontinuous Galerkin formulation in combination with oriented space-time meshes. A principle for mesh orientation in space-time based on minimization of the residual, related to adaptive error control via an a posteriori error estimate, is presented. The relation to Miller's moving finite element method is discussed. The article deals with scalar problems; systems will be treated in a companion article. © 1998 John Wiley & Sons, Inc. Numer Methods Partial Differential Eq 14:251-262, 1998
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    On convergence and performance of iterative methods with fourth-order compact schemes (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Numerical Methods for Partial Differential Equations 14 (1998), S. 263-280 
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    ISSN: 0749-159X
    Keywords: Convection-diffusion equation ; iterative methods ; fourth-order compact discretization schemes ; Mathematics and Statistics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Notes: We study the convergence and performance of iterative methods with the fourth-order compact discretization schemes for the one- and two-dimensional convection-diffusion equations. For the one-dimensional problem, we investigate the symmetrizability of the coefficient matrix and derive an analytical formula for the spectral radius of the point Jacobi iteration matrix. For the two-dimensional problem, we conduct Fourier analysis to determine the error reduction factors of several basic iterative methods and comment on their potential use as the smoothers for the multilevel methods. Finally, we perform numerical experiments to verify our Fourier analysis results. © 1998 John Wiley & Sons, Inc. Numer Methods Partial Differential Eq 14:263-280, 1998
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    An accurate semi-analytic finite difference scheme for two-dimensional elliptic problems with singularities (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Numerical Methods for Partial Differential Equations 14 (1998), S. 281-296 
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    ISSN: 0749-159X
    Keywords: singularities ; elliptic PDE ; Laplace equation ; high-order Finite Difference Schemes ; Mathematics and Statistics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Notes: A high-order semi-analytic finite difference scheme is presented to overcome degradation of numerical performance when applied to two-dimensional elliptic problems containing singular points. The scheme, called Least-Square Singular Finite Difference Scheme (L-S SFDS), applies an explicit functional representation of the exact solution in the vicinity of the singularities, and a conventional finite difference scheme on the remaining domain. It is shown that the L-S SFDS is “pollution” free, i.e., no degradation in the convergence rate occurs because of the singularities, and the coefficients of the asymptotic solution in the vicinity of the singularities are computed as a by-product with a very high accuracy. Numerical examples for the Laplace and Poisson equations over domains containing re-entrant corners or abrupt changes in the boundary conditions are presented. © 1998 John Wiley & Sons, Inc. Numer Methods Partial Differential Eq 14: 281-296, 1998
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    Qualitative behavior of numerical solutions to an s-i-s epidemic model (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Numerical Methods for Partial Differential Equations 14 (1998), S. 317-337 
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    ISSN: 0749-159X
    Keywords: s-i-s epidemic model ; finite difference ; method of characteristics ; asymptotic behavior ; periodic solution ; Mathematics and Statistics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Notes: A finite difference scheme along the characteristics is used to approximate the solution of an age-dependent s-i-s epidemic model. The global behavior of the discrete solution resulting from the algorithm is investigated. It is shown that a nontrivial discrete periodic solution is generated by a periodic force of infection. Sufficient (and explicit) threshold conditions for the existence and stability of a unique nontrivial periodic solution are given. Results from numerical experiments are presented. © 1998 John Wiley & Sons, Inc. Numer Methods Partial Differential Eq 14: 317-337, 1998
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    Mesh-centered finite differences from nodal finite elements for elliptic problems (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Numerical Methods for Partial Differential Equations 14 (1998), S. 439-465 
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    ISSN: 0749-159X
    Keywords: mesh-centered finite differences ; nodal methods ; elliptic problems ; Mathematics and Statistics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Notes: After it is shown that the classical five-point mesh-centered finite difference scheme can be derived from a low-order nodal finite element scheme by using nonstandard quadrature formulae, higher-order block mesh-centered finite difference schemes for second-order elliptic problems are derived from higher-order nodal finite elements with nonstandard quadrature formulae as before, combined to a procedure known as “transverse integration.” Numerical experiments with uniform and nonuniform meshes and different types of boundary conditions confirm the theoretical predictions, in discrete as well as continuous norms. © 1998 John Wiley & Sons, Inc. Numer Methods Partial Differential Eq 14: 439-465, 1998
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    Nonstandard methods for the convective transport equation with nonlinear reactions (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Numerical Methods for Partial Differential Equations 14 (1998), S. 467-485 
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    ISSN: 0749-159X
    Keywords: convection-reaction equations ; Lagrangian methods ; convective flows ; reactive solute transport problems ; exact finite difference schemes ; Mathematics and Statistics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Notes: A new nonstandard Lagrangian method is constructed for the one-dimensional, transient convective transport equation with nonlinear reaction terms. An “exact” time-stepping scheme is developed with zero local truncation error with respect to time. The scheme is based on nonlocal treatment of nonlinear reactions, and when applied at each spatial grid point gives the new fully discrete numerical method. This approach leads to solutions free from the numerical instabilities that arise because of incorrect modeling of derivatives and nonlinear reaction terms. Algorithms are developed that preserve the properties of the numerical solution in the case of variable velocity fields by using nonuniform spatial grids. Effects of different interpolation techniques are examined and numerical results are presented to demonstrate the performance of the proposed new method. © 1998 John Wiley & Sons, Inc. Numer Methods Partial Differential Eq 14: 467-485, 1998
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    A posteriori error estimates for nonlinear problems: Lr, (0, T; W1,ρ (Ω))-error estimates for finite element discretizations of parabolic equations (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Numerical Methods for Partial Differential Equations 14 (1998), S. 487-518 
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    ISSN: 0749-159X
    Keywords: A posteriori error estimates ; nonlinear parabolic PDEs ; time-dependent Navier-Stokes equations ; space-time finite elements ; θ-scheme ; Mathematics and Statistics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Notes: Using the abstract framework of [R. Verfürth, Math. Comput. 62, 445-475 (1996)], we analyze a residual a posteriori error estimator for space-time finite element discretizations of parabolic PDEs. The estimator gives global upper and local lower bounds on the error of the numerical solution. The finite element discretizations in particular cover the so-called θ-scheme, which includes the implicit and explicit Euler methods and the Crank-Nicolson scheme. As particular examples we consider scalar quasilinear parabolic PDEs of 2nd order and the time-dependent incompressible Navier-Stokes equations. © 1998 John Wiley & Sons, Inc. Numer Methods Partial Differential Eq 14: 487-518, 1998
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    A note on Hermitian splitting induced relaxation methods for convection-diffusion equations (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Numerical Methods for Partial Differential Equations 14 (1998), S. 581-591 
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    ISSN: 0749-159X
    Keywords: iterative methods ; Hermitian splitting ; successive overrelaxation ; convection-diffusion equation ; Mathematics and Statistics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Notes: The solution of the linear system Ax = b by iterative methods requires a splitting of the coefficient matrix in the form A = M - N where M is usually chosen to be a diagonal or a triangular matrix. In this article we study relaxation methods induced by the Hermitian and skew-Hermitian splittings for the solution of the linear system arising from a compact fourth order approximation to the one dimensional convection-diffusion equation and compare the convergence rates of these relaxation methods to that of the widely used successive overrelaxation (SOR) method. Optimal convergence parameters are derived for each method and numerical experiments are given to supplement the theoretical estimates. For certain values of the diffusion parameter, a relaxation method based on the Hermitian splitting converges faster than SOR. For two-dimensional problems a block form of the iterative algorithm is presented. © 1998 John Wiley & Sons, Inc. Numer Methods Partial Differential Eq 14: 581-591, 1998
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    Discretization of the stationary convection-diffusion-reaction equation (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Numerical Methods for Partial Differential Equations 14 (1998), S. 607-625 
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    ISSN: 0749-159X
    Keywords: convection-diffusion-reaction equation ; finite volume method ; exponential scheme ; flux computation ; Mathematics and Statistics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Notes: A finite volume method for the convection-diffusion-reaction equation is presented, which is a model equation in combustion theory. This method is combined with an exponential scheme for the computation of the fluxes. We prove that the numerical fluxes are second-order accurate, uniformly in the local Peclet numbers. © 1998 John Wiley & Sons, Inc. Numer Methods Partial Differential Eq 14: 607-625, 1998
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    Dimensional splitting with front tracking and adaptive grid refinement (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Numerical Methods for Partial Differential Equations 14 (1998), S. 627-648 
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    ISSN: 0749-159X
    Keywords: scalar conservation laws ; dimensional splitting ; front tracking ; error bounds ; adaptive grid refinement ; Mathematics and Statistics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Notes: Front tracking in combination with dimensional splitting is analyzed as a numerical method for scalar conservation laws in two space dimensions. An analytic error bound is derived, and convergence rates based on numerical experiments are presented. Numerical experiments indicate that large CFL numbers can be used without loss of accuracy for a wide range of problems. A new method for grid refinement is introduced. The method easily allows for dynamical changes in the grid, using, for instance, the total variation in each grid cell as a criterion for introducing new or removing existing refinements. Several numerical examples are included, highlighting the features of the numerical method. A comparison with a high-resolution method confirms that dimensional splitting with front tracking is a highly viable numerical method for practical computations. © 1998 John Wiley & Sons, Inc. Numer Methods Partial Differential Eq 14: 627-648, 1998
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    On the linear stability study of zonal incompressible flows on a sphere (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Numerical Methods for Partial Differential Equations 14 (1998), S. 649-665 
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    ISSN: 0749-159X
    Keywords: linear stability ; zonal flows ; Mathematics and Statistics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Notes: The normal mode (linear) stability of zonal flows of a nondivergent fluid on a rotating sphere is considered. The spherical harmonics are used as the basic functions on the sphere. The stability matrix representing in this basis the vorticity equation operator linearized about a zonal flow is analyzed in detail using the recurrent formula derived for the nonlinear triad interaction coefficients. It is shown that the zonal flow having the form of a Legendre polynomial Pn(μ) of degree n is stable to infinitesimal perturbations of every invariant set Im with |m| ≥ n. For each zonal number m, Im is here the span of all the spherical harmonics $Y^{m}_{k}(x)$, whose degree k is greater than or equal to m. It is also shown that such small-scale perturbations are stable not only exponentially, but also algebraically. © 1998 John Wiley & Sons, Inc. Numer Methods Partial Differential Eq 14: 649-665, 1998
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    Least squares methods for Volterra equations and generalizations (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Numerical Methods for Partial Differential Equations 14 (1998), S. 679-693 
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    ISSN: 0749-159X
    Keywords: least squares method ; finite element method ; Volterra equation ; Mathematics and Statistics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Notes: In this article least squares approximations to Volterra integral equations are considered, both with exact integration and with quadrature. Optimal error estimates are derived, and it is shown that the same order of convergence is obtained in both cases with only modest requirements on the quadrature rule used in the latter. The most important practical setting for least squares is the case of convolution kernels, and these are also studied in this article. © 1998 John Wiley & Sons, Inc. Numer Methods Partial Differential Eq 14: 679-693, 1998
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    The Method of Fundamental Solutions for Stokes flows with a free surface (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Numerical Methods for Partial Differential Equations 14 (1998), S. 667-678 
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    ISSN: 0749-159X
    Keywords: Method of fundamental solutions ; elliptic boundary value problems ; Stokes flow ; free surface ; Mathematics and Statistics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Notes: We investigate the use of the Method of Fundamental Solutions (MFS) for solving Stokes flow problems with a free surface. We apply the method to the creeping planar Newtonian extrudate-swell problem and study the effect of the surface tension on the free surface. The results are in good agreement with existing finite element and boundary element solutions. © 1998 John Wiley & Sons, Inc. Numer Methods Partial Differential Eq 14: 667-678, 1998
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    A family of ELLAM schemes for advection-diffusion-reaction equations and their convergence analyses (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Numerical Methods for Partial Differential Equations 14 (1998), S. 739-780 
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    ISSN: 0749-159X
    Keywords: advection-diffusion-reaction transport equations ; characteristic methods ; error estimates ; Eulerian-Lagrangian methods ; Mathematics and Statistics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Notes: A family of ELLAM (Eulerian-Lagrangian localized adjoint method) schemes is developed and analyzed for linear advection-diffusion-reaction transport partial differential equations with any combination of inflow and outflow Dirichlet, Neumann, or flux boundary conditions. The formulation uses space-time finite elements, with edges oriented along Lagrangian flow paths, in a time-stepping procedure, where space-time test functions are chosen to satisfy a local adjoint condition. This allows Eulerian-Lagrangian concepts to be applied in a systematic mass-conservative manner, yielding numerical schemes defined at each discrete time level. Optimal-order error estimates and superconvergence results are derived. Numerical experiments are performed to verify the theoretical estimates. © 1998 John Wiley & Sons, Inc. Numer Methods Partial Differential Eq 14: 739-780, 1998
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    The effects ofTilapia introductions in Lake Luhondo, Rwanda (1990)
    Springer
    Environmental biology of fishes 27 (1990), S. 303-308 
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    ISSN: 1573-5133
    Keywords: Fish introductions ; Africa ; Cichlids ; Barbus ; Haplochromis ; Lake management ; Fisheries
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Synopsis Cyprinid fishes apparently constituted the major part of the original fish fauna in Lake Luhondo, Rwanda, at least until 1934. At that time only three species, all cyprinids, were known from the lake:Barbus neumayeri, a small barbel, very common in the lake (described from the lake asBarbus luhondo) and two larger cyprinid species:Barbus microbarbis andVaricorhinus ruandae. These two large species were probably not very common in the lake. Between 1935 and 1938 some youngTilapia were introduced into Lake Luhondo. Since then and certainly since 1952 the large cyprinids seem to have disappeared completely from the lake. The smallBarbus neumayeri has become extremely rare; at present it survives only in some small tributaries of the lake. In the lake itselfTilapia andHaplochromis species are now the dominant fauna. A survey of the available information is given.
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    Masthead (1990)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 123 (1990) 
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    ISSN: 0009-2940
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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    URL: http://dx.doi.org/10.1002/cber.19901230101
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    Chrom-Komplexe mit cyclo-Asx-Liganden (1990)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 123 (1990), S. 3-6 
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    ISSN: 0009-2940
    Keywords: Pentaarsacyclopentadienyl ligand / Triarsachromatertrahedranes / Triple-decker complexes / Tetrahedrane, triarsachroma- ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Chromium Complexes with cyclo-Asx, LigandsThe interaction of [(η5C5Me4R)(CO)2Cr]2(Cr≡Cr) (1a: R = CH3 1b: R = C2H5) with yellow arsenic (As4) affords the triarsachromatetrahedranes [(η5-C5Me4R)(CO)2Cr(η3-As3)] (2a, b) as well as the 27-VE triple-decker complexes [{(η5-C5Me4R)Cr}2-(μ,η5-As5)] (3a, b) 3 is also formed photochemically from 2. 2a and 3b have been characterized by X-ray structure analyses. The cyclo-As5 ligand forms a regular arsenic pentagon.
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    Bindung von Monosacchariden über die Isocyano- und Carben-Funktion an das Metall-Atom: Chrom(0), Wolfram(0)-, Rhodium(III)-, Iridium(III)-, Palladium(II)-, Platin(II)- und Gold(I)-Komplexe von 1,3,4,6-Tetra-O-acetyl-2-desoxy-2-isocyano-α-D-glucose und - β-D-glucose (1990)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 123 (1990), S. 11-17 
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    ISSN: 0009-2940
    Keywords: Isocyanide complexes / Carbene complexes / Transition metal complexes / Carbohydrates / Glucose, 2-deoxy-2-isocyano-, as complex ligand ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Metal-Complexes of Biologically Important Ligands, LII. - Binding of Monosaccharides through the Isocyano and Carbene Group to the Metal Atom: Chromium(O), Tungsten(O), Rhodium(III), Iridium(1II). Palladium(I1). Platinum(ZI), and Gold(1) Complexes of 1.3.4.6-Tetra-O-acetyl-2-deoxy-2-isocyano-α-D-glucose and -β-D-glucoseStable isocyanide complexes cis-Cl2Pd(CNR)2 (2), cis-Cl2Pt(CNR)2 (3), cis-Cl2Pt(PPh3)CNR (4), [trans-(Ph3P)2Pt(Cl)CNR]+BF-4 (5), ClAuCNR (6), (OC)5CrCNR (7), (OC)5WCNR (8), (η5-C5Me5)Rh-(CNR)Cl2 (9), (η5-C5Me5)Ir(CNR)Cl2 (10) of 1,3,4,6-tetra-O-acetyl-2-deoxy-2-isocyano-α(β)-D-glucose (CNR) as well as carbene complexes ClAuC(NHR')(NHR) (11, 12) and cis-Cl2Pt(PPh3)C-(OR')NHR (13, 14) have been prepared and characterized by their IR and NMR spectra. The structure of 10 has been determined by X-ray crystal structure analysis.
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    Übergangsmetall-substituierte Acylphosphane und Phosphaalkene, XII1. - Übergangsmetall-Schwefelylid-Komplexe, XXVII2) Zur Umwandlung des Phosphaalkenyleisen-Komplexes (η5-C5Me5)-(CO)2FeP=C(SiMe3) 2 in η3-Phosphaallyleisen-Komplexe mittels Me2S(O)=CH2: Synthese und Molekülstruktur der beiden Isomeren von (η5-C5Me5)(CO)Fe{η3-P[CH(SiMe3)2](CHC=O)} (1990)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 123 (1990), S. 23-28 
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    ISSN: 0009-2940
    Keywords: Phosphaallyl complexes / Sulfur ylides ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Transition-Metal-Substituted Acylphosphines and Phosphaalkenes. XII. - Transition-Metal Sulfur Ylide Complexes, XXVIIzt - Conversion of a Phosphaalkenyliron Complex (η5-C5Me5)-(CO)2FeP=(SiMe3)2 into (η3-Phosphaallyl)iron Complexes by means of Me2S-(O)=CH2: Synthesis and Molecular Structures of Two Isomeres of (η5-C5Me5)-(CO)η5-P(CH-(SiMe3)2(CHC-0)}The transition-metal-substituted phosphaalkene (η5-C5Me5)-(CO)2FeP=C(SiMe3)2 (1) reacts with the sulfur ylide Me2S-(O)=CH2 (2) to afford the yellow η3-phosphaallyliron complex 4 with a syn-configuration in the organophosphorus ligand. In toluene solution at 40°C this complex undergoes an isomerization to the corresponding anti-configurated complex 5. Constitution and configuration of both compounds were elucidated by spectroscopic methods (IR, 1H, 13C, 31P NMR, and MS) as well as single-crystal X-ray diffraction analyses.
    Additional Material: 2 Ill.
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    URL: http://dx.doi.org/10.1002/cber.19901230106
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    Diphosphabicyclobutane (1990)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 123 (1990), S. 67-69 
    Details
    ISSN: 0009-2940
    Keywords: Diphosphabicyclobutanes / Valence isomerization ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: DiphosphabicyclobutanesTwo isomeric diphosphabicyclobutanes (5,11) are obtained by treatment of the phosphaalkenes X-P = C(Ph)Tms (1a) and X - P = CTms2 (1b) (X = halogen Tms = trimethylsilyl) with 2, Mg, or Na. Both syntheses proceed by coupling of two phosphaalkene units affording, however, two different diphospha-butadiene intermediates. 4 and 10 readily undergo isomerization reactions to form the diphosphabicyclobutanes. Irradiation of the phosphaalkenes Cp* - P = C(Ph)Tms (12a) and Cp* - P = CTms2 (12b) (Cp* = C5Me5) gives rise to a different reaction pathway. Dimerization of 12a, followed by homolytic cleavage of the Cp* - phosphorus bond and intramolecular recombination produces the butterfly compound 5, whereas homolytic cleavage of the Cp* - element bond in 12 b, followed by rearrangement and intermolecular recombination, affords the diphosphabicyclobutane 11.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19901230113
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    Mononuclear Bis(diazadiene)ruthenium(0) Complexes and the Coupling of Butadiene to a Diazadiene System (1990)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 123 (1990), S. 83-85 
    Details
    ISSN: 0009-2940
    Keywords: Diazadienes/Carbon-carbon coupling/Ruthenium(0) complexes/Ethylene complexes ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Complexes (dad)2RuCl2 (1) (dad = diazadiene, RN = CR'- CR'=NR) are reduced to (dad)2Ru (2) which react with L = CO or ethylene to give (dad)2RuL (3,5). Reduction of 1b ( R' = H) with magnesium-butadiene or reaction of 2b with butadiene leads to a new type of C-C coupling of butadiene to one of the diazadiene ligands (6b). Addition of CO induces a rearrangement to 7b by a hydride shift.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19901230117
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  • 50
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    Light-Induced Conversion of 4,6,7,8-Tetrahydro-2H-benzopyran-2,5(3H)-diones into 3,5,6,7-Tetrahydrobenzofuran-4(2H)-ones in Methanol (1990)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 123 (1990), S. 101-105 
    Details
    ISSN: 0009-2940
    Keywords: Enol lactones, photochemistry of / Ketene photoextrusion / Ketones, photoreduction / 0-Heterocycles, photochemistry of ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The photochemical conversion of 4,4,7,7-tetramethyl-4,6,7,8-tetrahydro-2H-benzopyran-2,5(3H)-dione (1) into 3,3,6,6-tetramethyl-3,5,6,7-tetrahydrobenzofuran-4(2H)-one (4) in methanol does not - as previously assumed - proceed by decarbonylation of the primarily formed acyl-vinyloxy biradical 2. This conclusion results from the finding that C-2, i. e. the CH2 group, of benzofuranone 4 stems from the solvent. Similar observations were made for other benzopyrandiones 15. A reaction sequence consisting of (a) ketene elimination from 2 with formation of 2-isopropylidene-5,5-dimethyl-1,3-cyclo-hexanedione and (b) light-induced (reductive) H . and . CH2OH addition to this intermediate followed by cyclization and dehydration to 4, is proposed for the conversion 1→4.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19901230121
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    Synthese von Sieben- und Achtring-anellierten Pyridinen durch “inverse” intramolekulare Diels-Alder-Reaktion mit Trifluormethyl-substituierten 1,2,4-Triazinen (1990)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 123 (1990), S. 133-136 
    Details
    ISSN: 0009-2940
    Keywords: 1,2,4-Triazines / Dienophiles, side-chain / [4+21 Cycloaddition / Pyrido[2,3-e-l,4-diazepines / Pyrido[2,3-b]-1,5-diazocines ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Synthesis of Seven- and Eight-Membered Ring-Annulated Pyridines by “Inverse” Intramolecular Diels-Alder Reaction with Trifluoromethyl-Substituted 1,2,4-TriazinesIntramolecular [4 + 2] cycloaddition reactions with inverse electron demand of trifluoromethyl-substituted 1,2,4-triazines carrying 7- or 8-membered o-alkyne side-chain dienophiles (3,8,12) lead to the synthesis of bicyclic pyridines with annulated heterocyclic seven- (5, 9, 13-15) or eight-membered rings (19, 22, 23, 26).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19901230125
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    Synthesen und Strukturen neuer Komplexes des 2,2′-Bipyridins mit Niob, Molybdän, Wolfram und Rhenium in hohen Oxidationsstufen (1990)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 123 (1990), S. 271-276 
    Details
    ISSN: 0009-2940
    Keywords: Niobium complexes / Molybdenum complexes / Tungsten complexes / Rhenium complexes ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Syntheses and Structures of New 2,2′-Bipyridine Complexes of Niobium, Molybdenum, Tungsten, and Rhenium in High Oxidation StatesExchange of oxo for chlorine ligands by means of hexamethyl-disiloxane provides an easy and effective synthesis of the oxo halides (bipy)MVOCl3 (bipy = 2,2′-bipyridine, C10H8N2; M = Nb, 1c; Re, 2c; W, 3c) and (bipy)MVIO2Cl2 (N = Mo, 6a;W, 6b). Starting from ReCl5 the structurally (X-ray) characterized byproduct (bipy)ReIVCl4 (2b) is also formed. Dirhenium heptaoxide (7) is converted into the complex (bipy)ReVIIO3Cl (8) upon treatment with chlorotrimethylsilane in the presence of 2,2′-bipyridine, thus being now easily available a key compound in rhenium chemistry. The new imido complexes of composition (bipy)MoVI(NR)2Cl2 [R = C(H3)3, 9a; C6H5, 9b] are accessible from 6a and the corresponding silylated amines. The rhenium and tungsten complexes 2b and 6b, resp., exhibit octahedral structures in the crystal, with that of 6b being distorted as a result of different ligands and intermolecular contacts.
    Additional Material: 1 Ill.
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    URL: http://dx.doi.org/10.1002/cber.19901230208
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    Ungewöhnliche Reaktion eines Diazaphosphetidinthions mit Trimethylsilylazid (1990)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 123 (1990), S. 289-292 
    Details
    ISSN: 0009-2940
    Keywords: Diazaphosphetidinethione / Trimethylsilyl azide / Migration, methyl group, trimethylsilyl group ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Unusual Reaction of a Diazaphosphetidinethione with Trimethylsilyl Azide2-Dimethylamino-1,3-dimethyl-1,3-diaza-2-phosphetidine-4-thione (1) and trimethylsilyl azide do not react with formation of the expected phosphane imine 2. Instead, (a) addition of trimethylsilyl azide to the °C=S group of 1, (b) sulfurization of the phosphorus atom of 1 and formation of the racemic thiophosphoryl compound 3 (as a result of intramolecular methyl/trimethylsilyl migration) take place. For 3 two pairs of diastereomers are discussed, which have been studied by 1H-, 13C- and 31P-NMR spectroscopy, and through a 1H-13C NMR correlation.
    Additional Material: 1 Ill.
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    URL: http://dx.doi.org/10.1002/cber.19901230211
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    Photo Diels-Alder Additons, V1 1,4-Photoadditions of α-Morpholinoacrylonitrile to 1-Acylnaphthalenes (1990)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 123 (1990), S. 315-319 
    Details
    ISSN: 0009-2940
    Keywords: Cycloadditions, regio- and stereoselective, light-induced / 1,4-Ethanonaphthalenes / Captodative alkenes / Di-π-methane rearrangement ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Photoexcited 1-naphthaldehyde (1a), 1-acetonaphthone (1b), and 1-naphthophenone (1c) add α-morpholinoacrylonitrile (2a) in a [4 + 2] mode with exceptional regio- and stereoselective formation of only one diastereomer of the two possible regioisomeric 1,4-dihydro-1,4-ethanonaphthalene adducts. An independently formed 1,2-adduct 4 was detected and isolated in very low yield, 4 is thermally and photochemically (313-nm, excitation) cleaved into the starting materials with no indication of direct interconversion into 3b. Compound 3b is stable towards 313-nm radiation, but is efficiently isomerized to give the dihydrobenzosemibullvalene 7 upon 254-nm excitation. - All observations point to the first excited triplet state as the starting point for the 1,4-additions.
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    URL: http://dx.doi.org/10.1002/cber.19901230216
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    Stereochemistry of Dewar Benzenes - Molecular Structures Influenced by Electronic and Steric Effects (1990)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 123 (1990), S. 345-350 
    Details
    ISSN: 0009-2940
    Keywords: Dewar benzene, derivatives, molecular structures of / Substituent effects on molecular structure ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The molecular structures of the four Dewar benzene derivatives 4-7 were determined by means of X-ray diffraction. The central C1-C4 bonds are extremely long. The carboxylate groups on the bridgehead carbon atoms of 4, 5, and 7 are in optimal orientation for an electronic interaction with the central bonds having high p-character. Therefore the central bonds in 4, 5, und 7 (1.602-1.612 Å) are even more elongated than in 6 (1.563 Å). Repulsion between tert-butyl groups causes bond lengthening and structural deformations. The sp2-hybridized carbon atoms are pyramidalized. From structural comparison of Dewar benzene derivatives a strong correlation between the length of the central bond and the folding angle of the four-membered rings can be derived. A new rule has been established for the thermal stability of Dewar benzene derivatives.
    Additional Material: 3 Ill.
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    URL: http://dx.doi.org/10.1002/cber.19901230220
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    Neue wasserlösliche makrobicyclische Großhohlräume (1990)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 123 (1990), S. 375-379 
    Details
    ISSN: 0009-2940
    Keywords: Cyclophanes / Hostguest chemistry / Macrocyclic compounds / Phanes / Supramolecular chemistry ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: New Watersoluble Macrobicyclic CavitiesThe watersoluble macrobicyclic compounds 1, 3, 5a, and 5b have been synthesized for the first time bearing large endolipophilic cavities of different sizes and shapes. They were studied with respect to their interactions towards lipophilic guest compounds. The “in/out” isomerism of the hitherto largest endolipophilic cavities 4a, 4b, 5a, and 5b has been investigated by 1H-, 13C-NMR spectroscopy and FAB mass spectrometry. The absence of significant 1H-NMR high-field shifts in hostguest studies is attributed to the rigidity of cavities 1 and 3, whilst the isomeric cavities 5a and 5b contain very large openings. Orientational fluorescence spectroscopy investigations, however, suggest hostguest interactions of the isomers 5a and 5b with ammonium 8-anilino-1-naphthalenesulfonate (8,1-ANS).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19901230224
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    Elektrophile β-Bromierung und nucleophile α-Methoxylierung α,β-ungesättigter Carbonylverbindungen (1990)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 123 (1990), S. 399-404 
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    ISSN: 0009-2940
    Keywords: β-Halovinyl ketones / β-Halovinyl aldehydes / α-Alkoxyvinyl ketones ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Electrophilic β-Bromination and Nucleophilic α-Methoxylation of α,β-Unsaturated Carbonyl CompoundsOximes 29a, b, semicarbazones 11a-d, dimethylhydrazones 4, and [3-methyl-2(3H)-benzothiazolylidene]hydrazones 23a-c of unsaturated aldehydes and ketones are brominated at the β-carbon by an addition-elimination sequence (→ 21a,b, 13a-d, 7, and 27c, respectively). When unsaturated ketone hydrazones are treated with bromine and methanol the α-methoxy-β-bromo derivatives 35a-c are obtained, which after hydrolysis and hydrobromic acid elimination give α-methoxy substitution products 36a-c of the starting compounds.
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    URL: http://dx.doi.org/10.1002/cber.19901230227
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    Electron-Density Distribution in the Bonds of a Dewar Benzene Derivative (1990)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 123 (1990), S. 341-343 
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    ISSN: 0009-2940
    Keywords: Difference electron densities / Dewar benzene, derivative ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We determined the difference electron densities [X-X] in the bonds of a Dewar benzene derivative from low temperature X-ray data (94 K). The density maxima on all bonds are significant. The central bond with an internuclear distance of 1.594 Å has a strong bending character. From the difference densities a bending angle of 28° can be derived.
    Additional Material: 4 Ill.
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    URL: http://dx.doi.org/10.1002/cber.19901230219
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    Zur Stereoselektivität der intramolekularen Diels-Alder-Reaktion von 1,7,9-Decatrien-3-onen zu Octalonderivaten (1990)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 123 (1990), S. 363-374 
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    ISSN: 0009-2940
    Keywords: Diels-Alder reaction, intramolecular / 1,7,9-Decatrien-3-ones / Octalone derivatives / Siloxycyclopropanes ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Stereoselectivity of Intramolecular Diels-Alder Reactions of 1,7,Q-Decatrien-3-ones to Octalone Derivatives2-Alkenyl-substituted 2-siloxycyclopropanes 1 and 2 serve as protected enone equivalents and are converted into key building blocks 5-8 in excellent yields. After desilylation and ring cleavage these compounds provide 1,7,9-decatrien-3-ones 9-12, which undergo smooth intramolecular Diels-Alder reaction at room temperature or approximately 100°C. The resulting octalone derivatives 13-16 are formed with exclusive or preferred cis connection of the rings. The relative configurations of the cycloadducts are secured by equilibration experiments and NMR spectroscopy (selective proton decouplings). For 11 → 15 and 12 → 16 the cis selectivitiy can remarkably be enhanced by trifluoroacetic acid catalysis. This high noninduced diastereoselectivity is caused by the endo approach of the reactive molecular sites, whereas the configuration of the third stereogenic centre (C-2) is determined by the folding of the linking carbon chain. Preference of a boat conformation with equatorial ester group endo-Beq may be assumed and appears to be general for intramolecular cycloadditions of such trienones. This effect as well as the influence of further substituents at the diene or dienophile portion on stereoselectivity and the reactions of other model compounds are discussed.
    Additional Material: 8 Tab.
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    URL: http://dx.doi.org/10.1002/cber.19901230223
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    Novel Access to Polyazamacrocycles: Non-Template Cyclization of Terephthalaldehyde and Aliphatic Polyamines (1990)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 123 (1990), S. 405-406 
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    ISSN: 0009-2940
    Keywords: Polyazamacrocycles / Cyclization, non-template / Terephthalaldehyde / Polyamines ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Non-template [2+2] condensation of terephthalaldehyde with bis(3-aminopropyl)amine and N,N'-bis(3-aminopropyl)-1,2-diaminoethane leads to macrocyclic systems that can be reduced and derivatized further, whereas a similar reaction with bis(2-aminoethyl)amine leads to polymeric material only.
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    URL: http://dx.doi.org/10.1002/cber.19901230228
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    Deuterierte Bicyclo[3.2.0]heptan-2-one und ihre NMR-Spektren (1990)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 123 (1990), S. 411-412 
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    ISSN: 0009-2940
    Keywords: Bicyclo[3.2.0]heptan-2-one, deuterated ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Deuterated Bicyclo[3.2.0]heptan-2-ones and their NMR Spectra[3,3-2H2]-, [6,7-2H2]-, [6,6-2H2]-, and [7,7-2H2]bicyclo[3.2.0]heptan-2-ones were prepared, starting from 2-cyclopenten-1-one (1). Using these derivatives, the 13C- and 1H-NMR spectra of bicyclo[3.2.0]heptan-2-one (2) have been assigned.
    Additional Material: 2 Tab.
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    URL: http://dx.doi.org/10.1002/cber.19901230230
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    Die Borierung von Lactamen und Harnstoffen mit einem Amino-imino-boran (1990)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 123 (1990), S. 455-458 
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    ISSN: 0009-2940
    Keywords: N-Boryl lactams / Isourea, triborated / Isothiourea, triborated /N/O Borotropism / Calculations, MNDO ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Contribution to the Chemistry of Boron, 201. - Boration of Lactams and Ureas by an Amino-Imino-BoranePyrrolidon reacts with (tert-butylimino)(2,2,6,6-tetramethylpiperidino)borane (1) to give the N-borated lactam 2. Diketopiperazine behaves similarly. It is borated on both of its N atoms to form 3. Urea and 1 give access to the O,N,N′-triborated isourea derivative 4, which contains the structural unit of a ketiminoborane. The diborated carbodiimide 10 is ultimately obtained from 1 and thiourea via the triborated isothiourea derivative 9. MNDO calculations have been used to estimate the relative thermodynamic stabilities of O/N borotropes of carbonic acid amides and lactams. They demonstrate that the O isomers gain in stability by increasing the size of N substituents.
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    URL: http://dx.doi.org/10.1002/cber.19901230307
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    Lithium-Verbindungen eines Chlorsilanols und von Fluor-funktionellen Siloxanolen; Reaktionen und Kristallstrukturen (1990)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 123 (1990), S. 449-453 
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    ISSN: 0009-2940
    Keywords: Lithium salts / Chlorosilanol / Fluorosilanolates ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Lithium Compounds of a Chlorosilanol and of Fluoro-Functional Siloxanols; Synthesis and Crystal StructuresThe lithiated disilanol (CMe3)2Si(OH)2 (1) serves as a starting material in the reaction with halosilanes for the stepwise construction of siloxanols (4, 5, 7). 4 and 7 react with n-C4H9Li to give the lithium compounds 6 and 8, respectively. 6 crystallizes in hexane as a trimer with planar three-coordinated lithium, bonded to two Si-O atoms and one Si - F atom. 8 reacts in THF with LiF elimination to give cyclotrisiloxane 9. The chlorosilanol 2 is prepared by hydroxy-chlorine exchange in 1 with PCl5. The stable lithium derivative of 2 (3) forms a dimeric THF adduct with tetrahedral lithium.
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    Chemistry of the Heterocyclic Pseudobasic Amino Alcohols, XXXVIII Ring-Chain Tautomerism of Pyrimido[6,1-a]isoquinolines (1990)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 123 (1990), S. 493-498 
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    ISSN: 0009-2940
    Keywords: Pyrimido[6,1-a]isoquinolines / Pseudobases, heterocyclic / Ring-chain tautomerism ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In basis media, 4-substituted pyrimido[6,1-a]isoquinolin-2-imine hydrochlorides (4) constitute an equilibrium system involving the tautomeric forms characteristic of pseudobases 5, 6, 7 and the anhydro base 9. In aqueous solution in the pH range 7-13 the ammonium hydroxide form 5 is present. Between pH 13 and 14 the pseudobase 6 probably arises from this by covalent binding of the hydroxy group. 6 is then converted to the more stable imino type anhydrobase 9. Ring cleavage of 4 by excess alkali or of 9 by a small amount of water gives 1-(acylamidinomethylen)isoquinolines 7. Compounds 7 and 9 are stable in the solid state or in aprotic solutions but revert to cation 5 in dilute protic solutions.
    Additional Material: 2 Ill.
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    URL: http://dx.doi.org/10.1002/cber.19901230315
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    [2.2](2,6)- and [2.2](2,5)Pyrazinophanes: Synthesis and Molecular Structure (1990)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 123 (1990), S. 523-533 
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    ISSN: 0009-2940
    Keywords: Hofman 1,6-elimination / Pyrazine derivatives / [2.2]Pyrazinophanes ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The title compounds 1-3 and their methyl derivatives 4-7 were synthesized 2,11-dithia[3.3]pyrazinophanes 24-26 or by Hofmann 1,6-elimination of the appropriate [(5-methyl-2-pyrazinyl)methyl]trimethylammonium hydroxides followed by dimerization of the generated 2,5-dihydro-2,5-dimethylenepyrazines. α-Chlorination of the methylpyrazines 8-10 with N-chlorosuccinimide gave the required precursors 11, 12, 14, 17 and 18. The results of the X-ray structure determinations for 1-4 and 7 which indicate an unequivocal isomer assignment are discussed with regard to steric strain in these molecules. The electronic spectra of the pyrazinophanes 7-7 are reported and compared with those of the parent methylpyrazines.
    Additional Material: 6 Ill.
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    Asymmetric Induction in the Wittig-Still Rearrangement of Ethers Containing an Allylic Stereocenter - Diastereocontrol by Allylic Nitrogen (1990)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 123 (1990), S. 555-563 
    Details
    ISSN: 0009-2940
    Keywords: Kew Words: Asymmetric induction / Alcohols, homoallylic, diastereoselective synthesis of / γ-Amino alcohols, diastereoselective synthesis of / Hydrogen bonding / [2,3] Sigmatropic rearrangement / Wittig rearrangement ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The stereochemistry of Wittig-Still rearrangements under the influence of an allylic stereogenic center attached to Bn2N or RNBoc groups is studied. Rearrangements are subject to stereocontrol through asymmetric induction. Stannylated allyl ethers 13 with Z double bonds give syn-configuration amino alcohols 15 exclusively (ds 〉95 : 〈 5 - 〉 99.8 : 〈 0.2). Stannanes of E configuration 14 lead to 15 less selectively (syn :anti = 46 : 54 - 92 : 8). X-ray structural data are provided for amino alcohol syn-15b and for the bis(carbamate) 17.
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    Hetero-π-Systeme, 181 Hochsubstituierte 2,4-Di-tert-butyl-1-boracyclohexadiene (1990)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 123 (1990), S. 505-511 
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    ISSN: 0009-2940
    Keywords: Borabenzene / Sandwich complex / Steric crowding ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Hetero π-Systems, la. - Highly Substituted 2,4-Di-tert-butyl-l-boracyclohexadienesBoracyclohexadiees 14 and 16 with three bulky groups should be ideal starting materials for the preparation of kinetically stabilized borabenzene derivatives. They are formed by substitution reactions of anion 11, which itself is derived from 2,4-di-tert-1-methoxy-1-bora-2,5-cyclohexadiene (10) by lithiation. Reaction of lithium compound 11 with ferrous chloride provides the sandwich-type complex 12. As shown by X-ray structure analysis, 12 has C2 symmetry with the boron atoms in a syn arrangement in staggered conformation, an unusal feature for borabenzene complexes. Exchange of the methoxy group in the trimethylsilylated substance 16 leads to compounds 18a, 18b, 18c, 18d. Pyrolyses of the various precursors are described.
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    Synthese angularer Tetraquinane durch Photo-Thermo-Metathese diastereomerenreiner Benzochinon-Tetrahydropentalen-Addukte (1990)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 123 (1990), S. 549-554 
    Details
    ISSN: 0009-2940
    Keywords: Metathesis, photo-thermo / Tetraquinanes ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Synthesis of Angularly Annulated Tetraquinanes by Photo-Thermo Metathesis of Diastereomerically Pure Adducts Between Benzoquinone and TetrahydropentalenesA retrosynthesis is presented for an angularly fused tetraquinane, the central step of which is the photo-thermo metathesis of a tetrahydropentalene - benzoquinone adduct. A sequence of Michael addition/condensation reaction gives the 3-methyl- l-phenyl-1,2-dihydropentalene (2) in 70% yield from benzalacetone and cyclopentadiene. Reaction with lithium aluminum hydride lead to a 1.0: 1.0:0.8 mixture of the 1,2,3,4-tetra-hydropentalenes 4a and 4b and the 1,2,3,5tetrahydropentalene 5. This reaction is highly diastereoselective (d.s. 〉 96%) and provides the cis compounds exclusively. Diels-Alder cycloadditon of 4a, b and 5 to benzoquinone also proceeds highly stereoselectively. The adducts 7a, b and 8 may be separated by fractional crystallization. Their relative configuration can be determined by means of 2D-COSY and NOE experiments. The endo arrangement is demonstrated by the photoreactivity of the cycloadducts. Gas-phase thermolysis (700°C/0.05 Torr) of the cage molecules 9a and 9b (from irradiation in benzene) gives the angularly annulated tetraquinanes 10a and 10b in 95 and 88% yield, respectively.
    Additional Material: 3 Tab.
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    Zur Reaktion des Diphosphenyl-Komplexes (η5-C5Me5)(CO)2Fe - P=P - Aryl (Aryl = 2,4,6-tBu3C6H2) mit elektronenarmen Alkenen. Röntgenstrukturanalyse des Diphosphetans (1990)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 123 (1990), S. 733-738 
    Details
    ISSN: 0009-2940
    Keywords: Diphosphene complexes / 1,2-Diphosphetanes ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Transition-Metal-Substituted Diphosphenes, XVIII1). - On the Reactivity of the Diphosphenyl Complex (η5-C5Me5)(CO)2Fe - P=P - Aryl (Aryl = 2,4,6-tBu3C6H2) with Electron-Deficient Alkenes. X-ray Analysis of the Diphosphetane The transition-metal-substituted diphosphene (η5-C5Me5)(CO)2Fe - P=P - Aryl (1) reacts with fumarodinitrile (2a) to give the 1,2 diphosphetane all-trans- as the result of a [2 + 2] cycloaddition. Similarly, compound 1 is converted by either dimethyl fumarate (2b) or dimethyl maleate (2c) into the same cycloadduct all-trans- (3b). Diphosphetane 3a was completely characterized by a single-crystal X-ray analysis.
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    Ein neuer Zugang zu enantiomerenreinen β-Lactamen aus α-Aminosäuren durch präparative Anwendung der Isonitril-Nitril-Umlagerung (1990)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 123 (1990), S. 635-638 
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    ISSN: 0009-2940
    Keywords: β-Lactams / Isonitrile-nitrile rearrangement / α-Amino acids ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A New Approach to Enantiomerically Pure β-Lactams from a-Amino Acids by Applying the Isonitrile-Nitrile Rearrangement(S)-Phenylalanine (1) was converted into (S)-3-benzyl-2-azetidinone (8b) by a multistep reaction sequence. The key step of this approach is a stereospecific isonitrile-nitrile rearrangement (3 → 4) by flash pyrolysis, which may be performed in 20-g batches of 3. An improved procedure for the preparation of (S)-Phenylalaninol (2a) is described.
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    URL: http://dx.doi.org/10.1002/cber.19901230333
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    Masthead (1990)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 123 (1990) 
    Details
    ISSN: 0009-2940
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19901230401
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    Alkinverbrückte Vierkerncluster durch Expansion von Dreikernclustern (1990)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 123 (1990), S. 677-684 
    Details
    ISSN: 0009-2940
    Keywords: Cluster expansion/Clusters, alkyne-bridged tetranuclear/Framework isomerism ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Alkyne-Bridged Tetranuclear Clusters by Expansion of Trinuclear ClustersUnder photochemical activation Fe2(CO)9 is a suitable reagent for the expansion of alkyne-bridged trinuclear clusters 1-7 (Fe3, FeCo2, FeNi2, RuCo2, FeCoNi, RuCoNi, RuCoMo) to the corresponding tetranuclear clusters 9-15 containing Fe(CO)3 building blocks. The analogous incorporation of RhCp building blocks was possible by heating RhCp(CO)2 together with the alkyne-bridged Fe3, FeCo2, RuCo2, RuCoMo, and RuCoW clusters 1, 2a, 4, 7, and 8. The resulting clusters 16-20 with octahedral M4C2 frameworks showed framework isomerism in two cases [RuFeCo2 (11a, b) and RuCoMoRh (19a, b)]. Crystal structure determinations were performed for the Fe4 and Fe3Rh clusters 9, 16 as well as for both isomers 19a, b of the RuCoMoRh cluster.
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    URL: http://dx.doi.org/10.1002/cber.19901230405
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    Wasserstoffübertragungen, 15 Zum Ablauf der Dehydrierung von Dihydroarenen durch Chinone (1990)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 123 (1990), S. 627-633 
    Details
    ISSN: 0009-2940
    Keywords: Hydrogen transfer / Dehydrogenation of dihydroarenes / Isotope effects / Quinones, dehydrogenation with chloranile ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Hydrogen Transfer Reactions, 15lI. - On the Transition State in the Dehydrogenation of Dihydroarenes by QuinonesIn the hydride abstraction from 1,2-dihydronaphthalene by o-chloroanile the regioselectivity correlates with the stability of the carbenium ions as shown by both kinetic tests and reactions of isotopomeric hydrogen donators. - The temperature dependence of primary isotope effects does not correspond with any of the categories for the transition state as proposed by Kwart2). This was examined for 1,4-cyclohexadiene and 9,10-dihydroanthracene by a Bell correction and the parameters of activation (AH/AD und [ΔEA]D/H). A VAT mechanism3) is proposed to explain both these results and the large primary isotope effects.
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    TiCl4/NaI - A Novel, Efficient Reagent for Mild Reduction of the N - O Bond in Amine N-Oxides and Nitrones (1990)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 123 (1990), S. 647-648 
    Details
    ISSN: 0009-2940
    Keywords: Titanium, low-valent / Amine N-oxides / Deoxygenation ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Heteroaromatic N-oxides and nitrones were readily and selectively deoxygenated to the corresponding bases or imines in excellent yields with the TiCl4/NaI reagent system.
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    URL: http://dx.doi.org/10.1002/cber.19901230336
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    Optical Resolution of [2,2]Paracyclophanes by High-Performance Liquid Chromatography on Tris(3,5-dimethylphenylcarbamates) of Celllulos and Amylose (1990)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 123 (1990), S. 841-845 
    Details
    ISSN: 0009-2940
    Keywords: Resolution, optical / Stationary phase, Chiral / Anylose carbamates / Celluslose carbamates / [3.2]Paracyclophanes, functionalized ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Optical resolution of 22 [2,2]paracyclophane derivatives was examined by high-performance liquid chromatography (HPLC) using tris(3,5-dimethylphenylcarbamates) of cellulose and amylose as chiral stationary phases. Most compounds were completely separated into enantiomers at least on one of the stationary phases. The preparation of hte new cyclophane derivatives 10, 11, 12, 14, 16, and 19 as wel as a new procedure for the synthesis of 4-fluoro-[2,2]paracyclophane (3) are described.
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    Pentamakrocyclische Tris-Kronen. - Selektive Bindung von Kationen, Anionen und Neutralverbindungen (1990)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 123 (1990), S. 859-867 
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    ISSN: 0009-2940
    Keywords: Crown compounds / Host-guest chemistry / Macropentacyclic compounds / Phanes / Supramolecular chemistry ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Pentamacrocyclic Tris-Crown Hosts. - Selective Binding of Cationic, Anionic, and Neutral Guest CompoundsThe tris-crown host compounds 1-4 were synthesized for the first time. The X-ray crystal structures of 2 and of the 1:3 complex of 1 and KSCN were determined. Whereas in the free crown 2 a less well preorganized molecular cavity is encountered, in the complex of 1 with KSCN one potassium ion is bound to each crown ether unit. One of the three SCN- anions is situated in the interior of the cavity and in addition is disordered in such a way as to be bound to the K+ using partially the S atom of the SCN- ion. Organic guest molecules like 1,2-, 1,3-, 1,5-, 2,6-, and 2,7-naphthalenediol as well as β-naphthol in acidic water solution are bound selectively in the interior of the cavities of the host molecules 2 and 3, but not by 1 and 4, the cavities of which seem to be too small and too large, respectively. In contrast, the binding of α-naphthol and of smaller phenolic guest molecules like phenol, resorcinol, pyrocatechol, phloroglucinol, pyrogallol, and 1,2,4-trihydroxy-benzene with the host 1-4 is much less pronounced (1H- NMR highfield shifts).
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    URL: http://dx.doi.org/10.1002/cber.19901230435
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    Radikalische Cyclisierung von Dienen, III Radikalische Cyclisierung von (R)-(-)-Carvon - Über den Einfluß von Charge-Transfer-Wechselwirkung auf den spezifischen Drehwert (1990)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 123 (1990), S. 901-905 
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    ISSN: 0009-2940
    Keywords: Radical-type cyclisation / Bicyclo[3.2.]octan-3-one, enantiomerically pure / Charge-transfer interactions ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Radical-Type Cyclisation of Dienes, 111. - Radical-Type Cyclisation of (R)-( - )-Carvone - On the Influence of Charge- Transfer Interactions on the Optical RotationUnder the conditions of radical cyclisation, a 1:1 diastereomeric mixture of (1R,2S,5R,R)-(+)- (2a) and (1R.2S,5R,6S)-(+)-6-methoxy-2,6-dimethylbicyclo[3.2.1]octan-3-ones (2b) is obtained from (R)-(-)-carvone in 70% yield. the configuration fo 2a and 2b were confirmed by X-ray structure analyses of their hydrazones 2d and 2e. The regio- and stereoselectivity of the radical cyclisation of 1 to 2a and 2b are discussed. The high value of the specific rotation [-555] of 2d is traced back to charge-transfer interactions between the endo-standing methoxy group at C-6 as electron donor and the dinitrophenyl-hydrazone group as electron acceptor.
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    Notizen / Notes Phosphorverbindungen ungewöhnlicher Koordination, 43 Hochfunktionalisierte λ3-Phosphinine aus 5,5-Dimethoxycyclopentadienen und einem kinetisch stabilisierten Phosphaalkin (1990)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 123 (1990), S. 935-937 
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    ISSN: 0009-2940
    Keywords: Key Words: Phosphaalkines / Diels-Alder reaction / λ3-Phosphinines ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Phosphorus Compounds with Unusual Coordination, 43. - Highly Functionalized λ3-Phosphinines from 5,5-Dimethoxycyclopentadienes and Kinetically Stabilized Phosphaalkyne1,2,3,4-Tetrachloro-5,5-dimethoxycyclopentadiene (5) is transformed into the λ3-phosphinine 10 by reaction with the phosphaalkyne 6; the bicyclic compound 7 is assumed to be the intermediate of the process. In an analogous way the reaction 14 + 6 yields the isomeric λ3-phosphinines 15 and 17.
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    “Tuning” CH/CC Bond-Activation Processes of Branched Amines by Choosing the Appropriate Gas-Phase Transition-Metal Ion (1990)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 123 (1990), S. 939-941 
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    ISSN: 0009-2940
    Keywords: Key Words: Transition-metal ions / Bond activation, CH and CC / Tandem mass spectrometry / Amines, aliphatic ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The mechanisms of the deceptively similar gas-phase chemistry of amine complexes RC(CH3)2CH2NH2/M+ (R = H, CH3 M = Fe, Co, Ni) are uncovered by the use of deuterium-labeled compounds. It is demonstrated that the details of CH/CC bond-activation reactions are strongly metal-ion-dependent, as is the product distribution itself.
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    Ein Cyclobutadiencarboxylat als Hetero-1,3-dien bei Diels-Alder-Reaktionen mit 2H-Azirinen (1990)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 123 (1990), S. 927-933 
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    ISSN: 0009-2940
    Keywords: Cyclobutadiene / [4 + 2] Cycloaddition / 2H-Azirine / Bridgehead olefins ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Antiaromatic Compounds, 26 - A Cyclobutadienecarboxylate as a Hetero-1,3-diene in Diels-Alder Reactions with 2H-AzirinesThe cyclobutadienecarboxylic ester 1 adds 2H-azirines (2a-1) to yield the oxaazatricyclic compounds 4a-f. Under thermolysis conditions cleavage of isobutylene and formation of tricyclic ketones occurs (4a, c-e → 7a-d). The Dear pyridone 11 arises from the photolysis of 7a. The structures of compounds 4b and 11 are confirmed by X-ray crystal structure analyses.
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    Beiträge zur Chemie der Halogensilan-Addukte, 20. Hexakoordinierte Verbindungen von Trichlorsilanen. - Darstellung, Kristall-und Molekülstruktur von RSiCl3·bipy (1990)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 123 (1990), S. 945-951 
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    ISSN: 0009-2940
    Keywords: Chlorosilanes ; hexacoordinated/Silicon complexes ; octahedral ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Hexacoordinated Compounds of Trichlorosilanes. - Preparation, Crystal and Molecular Structure of BSiCl3·bipyThe octahedral Si complexes CHCl2SiCl3·bipy (1), CCl3SiCl3·bipy (2), and Cl3SiCCl2SiCl3·bipy (3) are obtained by the reaction of the respective trichlorosilanes and 2.2′-bipyridine (bipy). Their composition is independent of the initial ratio of the components. X-ray structure determinations show the Si atoms of all three complexes to be octahedrally coordinated with the substituted methyl groups in axial positions. The configurations represent structures of least steric hindrance assuming spheric substituents and demonstrate the usefulness of this structural model for solid compounds (in contrast possibly to dissolved compounds) even for substitutents deviating strongly from this assumption. Bond lengths and angles agree with the presence of hexacoordinated complexes. Deviations from expected values are interpreted in terms of considerable steric interactions. 3 represents a case of strongly hindered coordination requiring interesting steric adjustments.
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    Metal Ion Binding by Amino Acids. Potassium Hydrogen L-Glutamate Monohydrate K(L-GluH)·H2O (1990)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 123 (1990), S. 1001-1004 
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    ISSN: 0009-2940
    Keywords: Amino acid complexes ; L-Glutamate complexes ; Hydrogen L-glutamate complexes ; Potassium hydrogen L-glutamate ; Hydrogen bonding ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The title compound is obtained by neutralization of aqueous solutions of L-glutamic acid with potassium hydroxide, and crystallization from aqueous methanol. The compound shows a pH of 7 in water at ambient temperature and an optical rotation [α]20D of -4.30 (c = 3.0). In the crystal (orthorhombic, space group P212121) the potassium ion is in a distorted trigonal-prismatic environment of six oxygen atoms of four different amino acids and of the water molecule. No nitrogen coordination is observed. Through the bridging function of some of the α-carboxylate oxygen atoms (O1, O2) and through complexation of the metal through the γ-carboxylate groups (O3), a layer-coordination polymer, with strings of potassium ions running parallel, is formed. The layers are cross-linked by hydrogen bonds involving the ammonium and γ-carboxylate functions as well as the water molecule.
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    Darstellung, Struktur und Stereoisomerie von 1,3-Di-tert-butyl-1,3,2,4-diazadistibetidinen (1990)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 123 (1990), S. 975-978 
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    ISSN: 0009-2940
    Keywords: 1,3,2,4-Diazadistibetidines, 1,3-di-tert-butyl- ; Geometrical isomers ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Synthesis, Structure, and Stereoisomerism of 1,3-Di-tert-butyl-l,3,2,4-diazadistibetidinesStarting from 1,3-di-tert-butyl-2,4-dichloro-1,3,2,4-diazadistibetidine a series of 1,3,2,4-diazadistibetidines [R-SbN-ttBu]2 with R = OMe (2), OPh (3), OtBu (4), N(Tms)2 (5), P(Tms)2 (6), Me (7), and tBu (8) has been synthesized. The NMR spectra prove most of the reaction products to be mixtures of geometrical isomers. The structure of trans-tetra-tert-butyldiaza-distibetidine 8a was confirmed by X-ray structure determination.
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    Synthese und Reaktionen von 2-Pyridylphosphan, 2-C5NH4-PH2 (1990)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 123 (1990), S. 989-993 
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    ISSN: 0009-2940
    Keywords: Phosphane ; 2-pyridyl- ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Synthesis and Reactions of 2-Pyridylphosphane, 2—C5NH4-PH2By reduction of diethyl 2-pyridylphosphonate (1) with LiAlH4 2-pyridylphosphane (2) is accessible in ≍80% yield. H/D exchange experiments and acid/base exchange reactions between 2 and PhPHLi or Ph2PLi show (2) to be a stronger pH acid than PhPH2 and Ph2PH. Silylation of the lithium phosphides 2-C5NH4-PRLi (R — H, SiMe3) with Me3SiCl affords the corresponding silyl derivatives 2-C5NH4-PR2 with CH3I or CH2Cl2 yields the mono- or bidentate secondary phosphanes 2-C5NH4-PHMe (6) and 2-C5NH4PHCH2PH-2-C5H4N (5), respectively. On treatment of 2 with CH3I or HCl the pyridinium salts [(2-C5NH4R)PH2]+X- (R — H, Me; X= Cl, I) are formed. However, coordination of 2 to transition metals in low oxidation states occurs by the phosphorus atom. Addition of the PH bonds in 2 to the activated C—C double bonds in acrylic acid esters, mesityl oxide, cinnamnic acid esters, and dimethyl vinylphosphonate leads to chiral P,N hybrid ligands with functional groups in the alkyl side chain.
    Additional Material: 3 Tab.
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    URL: http://dx.doi.org/10.1002/cber.19901230510
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  • 85
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    Präorganisierte Bis-ethine: Molekulare π-Pinzetten? (1990)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 123 (1990), S. 1097-1103 
    Details
    ISSN: 0009-2940
    Keywords: Bond formation, C-C ; Iron complexes ; Macrocycles ; Molecular tweezers ; Naphthalenophane ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Preorganized Bis-ethynes: Molecular π-Tweezers?1,8-Bis[(arylethynylphenyl)]naphthalenes of type V (e.g. 10, 11) and 1,8-bis[(arylethenylphenyl)]naphthalenes (6, 6a, 7, 7a) were synthesized for the first time. In contrast to the known 1,8-bis(arylethynyl)naphthalenes VI their “stereologs” 10 and 11 are thermally stabile. Yet they react with pentacarbonyliron to yield dinuclear transition metal complexes of the type 12, 13, i.e. a strained cyclophane macrocycle is formed by C-C bond formation. The X-ray analysis of the di-tert-butyl compound 11 shows that the peri substituents diverge, but with increasing distance from the naphthalene skeleton one of the arylethynyl units is bent to the opposite direction (Figure 2). The question whether the new molecular skeleton V can be viewed as molecular tweezers is discussed: as the hydrocarbons react irreversibly with transition metal carbonyls, they may rather be taken as “tweezers for single use”.
    Additional Material: 3 Ill.
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    URL: http://dx.doi.org/10.1002/cber.19901230524
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  • 86
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    Synthese und Eigenschaften kalamitischer Flüssigkristalle aus desoxygenierten Kohlenhydrat-Derivaten (1990)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 123 (1990), S. 1129-1135 
    Details
    ISSN: 0009-2940
    Keywords: Deoxy sugars ; Glycosyl cyanides ; Liquid crystals, chiral, thermotropic ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Synthesis and Properties of Calamitic Liquid Crystals from Deoxygenated Carbohydrate DerivativesTreatment of the L-arabino- and Llyxo-configurated glycals 1 and 7 with trimethylsily cyanide leads to the formation of the anomeric nitriles 2, 3 and 15, 17, respectively. The configurational assignments are based on hydrogenated products such as 6 or 8 and 10. Depending on the configurations of the olefinic nitril sugars, various hydrogenation results are observed using palladium/charcoal or the Wilkinson catalyst. Methanolysis provides the corresponding methyl esters. The preparation of liquid-crystalline derivatives follows the classical route. In comparing the properties of these saccharide-based liquid crystals with the corresponding cyclohexane derivatives, the dominant influence of the anomeric effect on the tendency for phase formation can be observed. Some of the novel derivatives show highly twisted cholesteric and wide blue phases.
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    URL: http://dx.doi.org/10.1002/cber.19901230528
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  • 87
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    Photochemical Dehydrogenation, Ring Contraction, and Ring Expansion of Hydrogenated Derivatives of Benzoxazino-benzoxazine, Quinoxalino-quinoxaline, and Bibenzothiazole (1990)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 123 (1990), S. 1149-1154 
    Details
    ISSN: 0009-2940
    Keywords: Photochemistry ; Benzoxazino-benzoxazines ; Quinoxalino-quinoxalines ; Bibenzothiazoles ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The photochemical properties of the title compounds have been investigated and compared. The benzoxazino-benzoxazine derivatives 1 are photochemically converted into hydrogenated oxazole derivatives. In some cases this ring contraction is accompanied by a dehydrogenation reaction whereby the heterocyclic ring system becomes aromatic. Hydrogenated quinoxalino-quinoxalines also undergo a photodehydrogenation reaction and become aromatic. However, a ring contraction yielding the imidazolyl system does not take place. The only investigated sulfur-containing analog has different properties. The stable form is the bibenzothiazole 23 which contains a five-membered heterocyclic ring system. Photochemically 23 rearranges under ring expansion to give the benzothiazino-benzothiazine 24.
    Additional Material: 1 Tab.
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    URL: http://dx.doi.org/10.1002/cber.19901230531
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  • 88
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    9,10-Phenanthrenocyaninatoeisen(II) (PhcFe) und axial koordinierte Isocyanid-Komplexe (1990)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 123 (1990), S. 1105-1110 
    Details
    ISSN: 0009-2940
    Keywords: 9,10-Phenanthrenocyaninatoiron(II) ; Isocyanide complexes ; Porphyrin derivatives ; Semiconductors, organic ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 9,10-Phenanthrenocyaninatoiron(II) (PhcFe) and Axially Coordinated Isocyanide Complexes9,10-Phenanthrenocyaninatoiron(II) (PhcFe) is synthesized from 9,10-dicyanophenanthrene (3) and pentacarbonyliron. PhcFe exhibits similar spectroscopic properties (UV/VIS and Mößbauer spectra) and similar oxidation potentials as 1,2-Naphthalocyaninatoiron(II) (1,2-NcFe) and Phthalocyaninatoiron(II) (PcFe). Isocyanides RNC (R = tBu, cHx, Bzl, Me2Ph) react with PhcFe to form the corresponding bisaxially substituted 9,10-phenanthrenocyaninatoiron(II) compounds 4-7. Reaction of PhcFe with 1,4-diisocyanobenzene (dib) yields the bridged complex [PhcFe(dib)]n.
    Additional Material: 2 Ill.
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    URL: http://dx.doi.org/10.1002/cber.19901230525
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  • 89
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    (E,Z) Equilibria, 12. Differential NMR Shielding by Phenyl, Assigned from Chemical Labelling and (Z,E) Equilibration (1990)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 123 (1990), S. 1137-1141 
    Details
    ISSN: 0009-2940
    Keywords: Allyl anion ; Differential NMR-shielding ; Schiff's bases ; Stereoselective substitution ; Isomerization, (Z,E) ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Unequivocal NMR assignments of the (E,Z) isomeric pairs 3 and 8 are possible by (Z,E) equilibration. Deprotonation of 2-methyl-1-phenylpropene (1) with n-BuLi under any conditions gives only a single allyl-metal derivative 2. Methylation of the latter gives the isomer (Z)-3, while deuteriolysis leads to the isotopically labelled derivative 6 of the olefin 1; this Proves the NMR assignments for 1 as well as the endo configuration of 2. The phenyl group gives rise to a differential shielding effect on the γ-carbon nuclei in methyl and methylene gropus along a CC double bond (ca, 7 ppm), and this effect is comparable to that along a CN double bond as in 8. The nitrile function in 5c is much less effective.
    Additional Material: 1 Tab.
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    URL: http://dx.doi.org/10.1002/cber.19901230529
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  • 90
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    Künstliche molekulare Anion-Wirte. Die Synthese eines chiralen bicyclischen Guanidinium-Salzes als funktionalisierte Ankergruppe für Oxo-Anionen (1990)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 123 (1990), S. 907-915 
    Details
    ISSN: 0009-2940
    Keywords: Molecular recognition / Anion host compound / Guanidmiun salt / Chiral synthesis ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Artificial Molecular Anion Hosts. Synthesis of a Chiral Bicyclic Guanidinium Salt Serving as a Functionalized Anchor Group for 0x0 AnionsStarting from 1-asparagine, the synthesis of the S,S-bis(hydroxymethyl)-substituted bicyclic guanidinium salt 3 is described, which is obtained in 20% overall yield with a diastereomeric excess de 〉 98%. The guanidinium compound 3 may serve as a binding module in the enantioselective recognition of oxo anions in polytopic abiotic receptors.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19901230442
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    Masthead (1990)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 123 (1990) 
    Details
    ISSN: 0009-2940
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19901230501
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  • 92
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    Diphosphinonitrenium and -phosphenium Cations, Jahn-Teller Distorted Allyl Systems (1990)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 123 (1990), S. 971-973 
    Details
    ISSN: 0009-2940
    Keywords: Calculations ; Jahn-Teller distortion ; Nitrenium ; Phosphenium ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Ab initio calculations at SCF, MCSCF, and ACPF level were performed on a series of the phosphenium- and nitreniumcation family. These show that they possess an allylic π-system with 4 electrons, which is distorted from planarity when the terminal groups of the allylic system are PR2 (R — H) fragments. The distortion is such as to adopt C2 symmetry, and is the consequence of Jahn-Teller distortion via mixing of the energy highest π2 orbital with an energetically low lying δ* orbital. The latter interaction is only operative if a symmetry breaking from C2v to C2 symmetry occurs. The importance of Jahn-Teller distortion on the biradical character in these systems is investigated by correlation calculations.
    Additional Material: 1 Ill.
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    URL: http://dx.doi.org/10.1002/cber.19901230506
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  • 93
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    Lineare Oligophosphaalkane, XXV. Synthese von Ph2P—CH2—PH2 und (ph2P—CH2)2PH durch Phosphinomethylierung von PH3 unter Phasentransferkatalyse (1990)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 123 (1990), S. 995-999 
    Details
    ISSN: 0009-2940
    Keywords: Phosphine ; Phosphinomethylation ; Phase-transfer catalysis ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Linear Oligophosphaalkanes, XXV1. - Synthesis of Ph2P—CH2—PH2 and (Ph2P—CH2)2PH by Phosphinomethylation of PH3 with Phase-Transfer CatalysisAlkylation of Ph2PH with CH2Cl2 under phase-transfer conditions in the system dichloromethane/toluene/water affords Ph2P-CH2Cl in high yields. Depending on the reaction conditions employed Ph2P-CH2Cl reacts with PH3 in the two phase system under phase-transfer catalysis (nBu4NCl) to yield the tertiary-primary methylenebis(phosphane) Ph2P-CH2-Ph2 (2) or the PH functional triphosphaalkane Ph2P-CH2-PH-CH2-PPh2 (3), respectively. Metallation of 2 and 3 with RLi (R = nBu, tBu) and subsequent reaction with Me3siCl yields the silyl derivatives 2e and 3b, respectively. The analysis of the 1H- 13C- and 31P-NMR spectra is reported.
    Additional Material: 2 Ill.
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    URL: http://dx.doi.org/10.1002/cber.19901230511
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    Organosubstituierte 1,6-Dioxa-2-sila-5-bora-3-cycloalkene - Herstellung und Charakterisierung (1990)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 123 (1990), S. 1013-1028 
    Details
    ISSN: 0009-2940
    Keywords: 1,2,5-Azasilaboroles, organo-2,5-dihydro- ; Dihydroxyalkanes(arenes) ; 1,6-Dioxa-2-sila-5-bora-3-cycloalkenes ; Regio- and stereoisomers ; Metathesis, BO ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Organosubstituted 1,6-Dioxa-2-sila-5-bora-3-cycloalkenes - Preparation and Characterisation1)The cis-alkenes ROSi(CH3)2C(R) = C(C2H5)B(C2H5)OR (R = CH3: 11; C2H5: 12; C6H5: 13) are prepared from CH3NSI[CH3)2C(R)=C(C2H5)BC2H5 [R = CH3: A; R = C(CH3) = CH2: B] with the monohydroxy compounds ROH (R = CH3, C2H5, C6H5). A or B react with aliphatic dihydroxy compounds HO—R′—OH [R′ = —CH2CH2—: 1; —CH(CH3)CH2—: 2; —CH(CH3)—CH(CH3)—: 3; —C(CH3)2C(CH3)2—: 4; —(CH2)3: 5; —(CH2)4—: 6] to give 8-, 9-, and 10-membered ring compounds OSi(CH3)2C(R) = C(C2H5)OR′ [15a,b, 16/16′, meso/rac-17a, D-17a,b, 18, 19, (20)n]. A is initially cleaved at the SiN bond with formation of 14 Compound 15a crystallises as the 16-membered (15a)2 [X-ray structure analysis). The aromatic dihydroxy compounds catechol (7), resorcinol (8), 2,3-dihydroxynaphthalene (9), 1, 8-dihydroxynaphthalene (10) react with A to form 21 to 24, but mainly by protolytic BCvinyl fission to give the 2,5-dihydro-1,2,3-dioxaboroles (e.g. 7f1, 9f1, 10f1) and the acyclic boron-free compounds 7f′3, 9f3, 10f3. The MS and NMR (1H, 11B, 13C, 29Si) data of the new compounds are discussed.
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    URL: http://dx.doi.org/10.1002/cber.19901230514
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    Reaktive E=C(p-p)π-Systeme, XXIII. Unerwartete Isomerisierung des Perfluorisopropylidenphosphans F3CP=C(CF3)2 zum Perfluorisopropenylphosphan F3CPF(F3C)C=CF2 (1990)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 123 (1990), S. 1047-1049 
    Details
    ISSN: 0009-2940
    Keywords: Perfluorophosphaalkenes ; Stannyl(perfluoroalkyl)phosphanes, Me3SnF elimination ; Perfluoro effect ; 1,3-Fluorine shift ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Reactive E = C(p-p)x-Systems, XXIII. - Unexpected Isomerization of Perfluoroisopropylidenephosphane F3CP = C(CF3)2 to the Perfluoroisopropenylphosphane F3CPF(F3C)C = CF3Elimination of Me3SnF from the stannylphosphane Me3Sn(F3C)PCF(CF3)2 (2) by gas-phase pyrolysis at 220°C surprisingly yields the isopropenyl phosphane F3CPFC(CF3)=CF2 (5) instead of the expected isopropylidene derivative F3CP=C(CF3)2 (4). In a similar manner, HF elimination from the phosphane HP(CF3)CF(CF3)2 (3) by passing its vapour over KOH pellets leads to 5. The formation of 5 is due to a spontaneous isomerization of the labile intermediate 4.
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    URL: http://dx.doi.org/10.1002/cber.19901230518
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    Carbonylierende Ringerweiterung, 4. Diastereoselektive Synthesen von Bicyclo[3.2.1]oct-3-en-2,8-dionen durch doppelte Carbonylierung von (R)-(-)-α-Phellandren (1990)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 123 (1990), S. 1079-1087 
    Details
    ISSN: 0009-2940
    Keywords: Ring enlargement ; Phellandrene ; Carbonylation ; Bicyclo[3.2.1]octanes, stereoselective syntheses of ; Iron complexes ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Carbonylating Ring Enlargement, 41). - Diastereoselective Syntheses of Bicyclo[3.2.l]oct-3-ene-2,8-diones by Double Carbonylation of (It)-(-)-α-PhellandreneIn order to clarify the stereochemistry of the carbonylating ring enlargement of cyclohexadiene complexes 1 to complexed seven-membered ring ketones 2 and the further carbonylation to bicyclo[3.2.1]oct-3-ene-2,8-diones 3 the exo and endo isomers of (R)-(-)-α-phellandrene complex 7 were synthesized in pure form and in various isomeric ratios and converted. The optically active ring-enlargement products 11 and 12 obtained therefrom, as well as the enantiomerically pure bicyclooctenes 20-22, implicate a stereospecific reaction course under retention of the configuration predetermined by the starting material 6 and its complexes 7. This was confirmed by an X-ray determination of the absolute configuration of exo-12. Thus, the method is suitable for the diastereoselective synthesis of bicyclo[3.2.1]oct-3-ene-2,8-diones 3 from 1,3-cyclohexadiene complexes 1.
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    URL: http://dx.doi.org/10.1002/cber.19901230522
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    Konformationsanalysen von pyrolytisch erzeugten [2.2]phanen des 4-Pyranons (1990)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 123 (1990), S. 1119-1128 
    Details
    ISSN: 0009-2940
    Keywords: Pyranophanes ; Sulfone pyrolysis ; Ring strain ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Conformational Analyses of [2.2]Phanes of 4-Pyranone Generated by PyrolysisThe synthesis of the first phanes of 4-pyranone is accomplished by pyrolysis of bis(sulfone) 4. Analogously, 9, 10 and 11 are synthesized. While 5is conformationally mobile in solution, 9 and 10 are fixed (up to 100°C) and exhibit anti conformation as shown by X-ray structural analysis (11). Like 9 and 11, 5, exists in a staircase-like structure in the crystal. 1H-NMR spectra of the metaparacyclophane 10 shows coalescence of the signals of the methylene protons at room temperature. The flexibility at 10 at 60°C is interpreted as a swinging process. The crystal structure of bis(sulfone) 8a shows that the two planar rings are tilted by 60°C with respect to each other.
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    Fourfold Diamond Structure of the Dipotassium and Disodium Salts of 1,3,5,7-Adamantanetetracarboxylic Acid (1990)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 123 (1990), S. 1111-1118 
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    ISSN: 0009-2940
    Keywords: Hydrogen bonding ; Superdiamond structures, multiple ; Helices, fourfold ; Ferroelectricity ; Metal chains, cationic ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The (isomorphous) crystal structures of the dipotassium and disodium salts of 1,3,5,7-adamantanetetracarboxylic acid are described. In the tetragonal, non-polar crystals of space group P42/nbc hte tetrahedral dihydrogen tetracarboxylate anions join to form four hydrogen-bonded superdiamond networks interpenentrating each other. The cations are arranged in chains (“metal-over-metal”] within fourfold helical channels (double antiparallel double-helices). The short, negatively charged O-H…O⊖ hydrogen bonds are symmetric on average. However, in the dipotassium salt actually disordered, asymmetric hydrogen bonds are likely to be present (double-minimum potential, O-H…O⊖ distance 2.52 Å). In analogy to potassium dihydrogen phosphate, KH2PO4, the present tetrahedral dipotassium dihydrogen tetracarboxylate may thus potentially form polar, ferroelectric crystals at low temperature with an ordered array of asymmetric hydrogen bonds. In the course of the crystallization of the disodium salt of adamantanetetracarboxylic acid, tetragonal crystals of a tetrahydrate of the tetrasodium salt were accidentally obtained (space group I41/α) and their structure determined. The arrangement of the hydrated anions may be characterized either as a hydrogen-bonded, distorted triple-diamond structure, or else aas a “semi-clathrate”, consisting of non-intersecting orthogonal water chains interpenetrating each other and tetracarboxylate tetraanions functioning as cross-links between these chains by means of hydrogen bonds.
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    URL: http://dx.doi.org/10.1002/cber.19901230526
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    Conformation of C-1-Substituted Pyranos-1-yl and Pyranosan-5-yl Radicals Evidence for a Quasi-Homo-Anomeric Stabilization Effect (1990)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 123 (1990), S. 1155-1160 
    Details
    ISSN: 0009-2940
    Keywords: Carbohydrate radicals ; Conformational analysis ; ESR spectroscopy ; Anomeric effect ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Acetylated 1-cyano- and 1-chloro-pyranos-1-yl radicals and 5-acetoxycarbonyl-, 5-methoxycarbonyl-, and 5-unsubstituted pyranosan-5-yl radicals were generated from the corresponding bromides by bromine abstraction with trimethyltin radicals. The conformation of these radicals, as deduced from the ESR hyperfine splittings, is explained by the combined action of a quasi-anomeric and a homo-anomeric stabilization effect. A captodative substitution pattern of the radical center does not influence the conformations.
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    URL: http://dx.doi.org/10.1002/cber.19901230532
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    N-[(2-Naphthyloxy)methyl] benzazoles: Synthesis and Investigation by X-ray Analysis and by Semiempirical MO Calculations (1990)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 123 (1990), S. 1185-1191 
    Details
    ISSN: 0009-2940
    Keywords: Calculations, AM1, PM3 ; Anomeric effect ; Conformationa. ana.;sis ; Benzazoles, N-substituted ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The crystal structures of 1-[(2-naphthyloxy)methyl]-lH-benzotriazole (4) and -1H-benzimidazole (8) and the 3-metho-quaternary iodide 9 derived from 8 are reported. The experimentally determined geometries are compared with the corresponding results from MNDO, AM1, and PM3 calculations. Remarkably, the crystal structures differ significantly from those calculated by AM1 as most stable. - Thus, conformations of 9 (from the crystal structure) and 9a (the most stable AM1 structure) differ in energy by ca. 3.5 kcal/mol. This stabilization of 9a is due to the anomeric effect which cannot be expressed in conformation 9. Calculations of the alternative cleavage of the methyl or of the naphthyloxymethyl cation (Figure 6) clarify discrepancies between the experimental and the calculated bond lengths.
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    URL: http://dx.doi.org/10.1002/cber.19901230536
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