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  • Biochemistry  (135)
  • Wiley-Blackwell  (135)
  • 2010-2014
  • 1980-1984  (135)
  • 1925-1929
  • 1983  (79)
  • 1980  (56)
  • 1928
Collection
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Years
  • 2010-2014
  • 1980-1984  (135)
  • 1925-1929
Year
  • 1
    Electronic Resource
    Electronic Resource
    Biochemistry of the polyamines (1983)
    New York, NY [u.a.] : Wiley-Blackwell
    Cell Biochemistry and Function 1 (1983), S. 131-140 
    Details
    ISSN: 0263-6484
    Keywords: Biochemistry ; polyamines ; putrescine ; spermidine ; spermine ; ornithine decarboxylase ; biosynthesis ; cell proliferation ; oxidized polyamines ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: The naturally-occurring polyamines exist in the free form, as N-acetyl derivatives and bound to protein. Their biosynthesis is subject to sensitive control, particularly of ornithine decarboxylase. This enzyme may be multifunctional and a key regulatory protein. Studies, principally with selective inhibitors, have elucidated the roles of polyamines in cell proliferation. Oxidized polyamines, in contrast, can be potent mitotic inhibitors. These effects are reviewed in terms of their chemistry and biochemistry. Their principal distinctions are that they can be made or degraded intracellularly, they can associate electrostatically with macromolecules by means of their spaced cationic groups, and these can be readily converted to covalent bonds.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cbf.290010302
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  • 2
    Electronic Resource
    Electronic Resource
    The C4H4CO potential surface. Reactions involving bicyclo[2.1.0]pentenone (1980)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 1 (1980), S. 129-133 
    Details
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: MNDO and MINDO/3 calculations were used to study the photochemical formation, thermal rearrangements, and dissociation of bicyclo[2.1.0]pentenone. The “forbidden” thermal conversion to cyclopentadienone requires little activation, which accounts for the low kinetic stability of bicyclo[2.1.0]pentenone. The theoretical results seem to be compatible with the available experimental evidence for the tri-tert-butyl-substituted systems and suggest an explanation for observed differences in reactivity.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540010204
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  • 3
    Electronic Resource
    Electronic Resource
    On the relative importance of core and valence shell representations in the calculation of conformational energies using small Gaussian basis sets (1980)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 1 (1980), S. 134-140 
    Details
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: Several “core-deficient” small Gaussian basis sets were constructed and analyzed in terms of the balance requirements of functions that contribute predominantly to the core. Variations in the conformational energy barriers and geometrical parameters for ammonia and ethane, calculated with these basis sets, were analyzed with a gradient technique. A scheme for the reduction of the size of molecular basis sets is proposed.
    Additional Material: 4 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540010205
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  • 4
    Electronic Resource
    Electronic Resource
    A note on density matrix extrapolation and multiple solutions of the unrestricted Hartree-Fock equations (1980)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 1 (1980), S. 178-180 
    Details
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: Unrestricted Hartree-Fock (UHF) SCF-MO calculations on the doublet reaction surface for the addition of methylidyne (CH) to ethylene (C2H4) using the standard extrapolation techniques of the GAUSSIAN 70 program show erratic behavior. On the other hand, the potential energy surface calculated without extrapolation of the density matrix and by using the final density matrix of a neighboring point as the initial guess for the density matrix for the new point gave a smooth potential curve without any kinks or erratic pattern. Therefore, the density extrapolation technique should be used with particular caution in UHF calculations.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540010210
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  • 5
    Electronic Resource
    Electronic Resource
    The torsional potential function for n-butane (1980)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 1 (1980), S. 181-184 
    Details
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: The energies of four different conformations for n-butane were calculated by the ab initio method using an STO-3G basis set. Fully relaxed molecular geometries obtained from molecular mechanics (MM2) were used. The two energy minima [anti (C2h), gauche (C2)] and the two maxima (C2, C2v) had the following relative energies: 0.0, 0.88, 3.56, 5.99 kcal/mole. These are approximate Hartree-Fock numbers. It is estimated that inclusion of electron correlation in the calculation would lower the last number to about 5.1 kcal/mole while leaving the first three values essentially unchanged.
    Additional Material: 3 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540010211
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  • 6
    Electronic Resource
    Electronic Resource
    Masthead (1980)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 1 (1980) 
    Details
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540010301
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  • 7
    Electronic Resource
    Electronic Resource
    The structure of carbon trioxide (1980)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 1 (1980), S. 199-203 
    Details
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: Open (1) and cyclic (2) singlet forms of CO3 were investigated by means of ab initio calculations. At the highest level of theory employed, MP2/6-31G* (which includes the effects of electron correlation), 2 was indicated to be much more stable than 1 and thermodynamically stable toward dissociation into CO2 and O(3P). The open form 1 has a long O—O bond and can be regarded as a weak dative complex between CO2 and a singlet oxygen atom.
    Additional Material: 3 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540010215
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  • 8
    Electronic Resource
    Electronic Resource
    A systematic preparation of new contracted Gaussian-type orbital sets. III. Second-row atoms from Li through ne (1980)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 1 (1980), S. 205-228 
    Details
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: Four minimal Gaussian basis sets are generated for the second-row atoms Li through Ne. The first one, MINI-1, consists of a 3-term contraction of primitive Gaussian-type orbitals for 1s, 2s, and 2p atomic orbitals. The convenient shorthand notation would be (3,3) for Li—Be and (3,3/3) for B—Ne. The second one, MINI-2, can be represented by (3,3/4) for B—Ne. In the same way, MINI-3 is described as (4,3) for Li—Be, and MINI-3 and MINI-4 are represented by (4,3/3) and (4,3/4) for B—Ne, respectively. Although the four basis sets are the minimal type, they give the valence shell orbital energies which are close to those of DZ. These four and other sets derived from them are tested for the hetero- and homodiatomic molecules and some organic molecules. They are found to give the orbital energies that agree well with those given by extended calculations. Atomization energies and other spectroscopic constants are also calculated and compared with those of extended calculations. The results clearly indicate that the present basis sets can be used very effectively in the molecular calculations.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540010302
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  • 9
    Electronic Resource
    Electronic Resource
    On the gearing of methyl groups in hexamethylbenzene (1980)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 1 (1980), S. 76-80 
    Details
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: Empirical force field calculations were performed on hexamethylbenzene to elucidate the internal motions of the methyl groups. When the benzene ring is constrained to be planar (as in solid-phase studies), the methyl groups undergo a geared, disrotatory motion. When this constraint is relaxed, results are force field dependent. Calculated barriers are in good agreement with experimentally determined values.
    Additional Material: 3 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540010110
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  • 10
    Electronic Resource
    Electronic Resource
    Atomic Xα calculations based on EHFS(α) = Eexp (1980)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 1 (1980), S. 88-93 
    Details
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: The total energies and one-electron energies for first- and second-row atoms were calculated by using the Hartree-Fock and the Hartree-Fock-Slater Hamiltonian with Xα orbitals, ui(αexp); α was parametrized from EHFS(αexp) = Eexp. The EHF(αexp) total energies are always higher than the Hartree-Fock energies for the atoms. The relation of the calculated ionization potential to the experimental ionization potential depends on the α used to define ui(α), αexp, or αHF.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540010112
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  • 11
    Electronic Resource
    Electronic Resource
    Masthead (1980)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 1 (1980) 
    Details
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540010201
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  • 12
    Electronic Resource
    Electronic Resource
    Molecular mechanics of organic halides. III. Fluorinated olefins (1980)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 1 (1980), S. 111-117 
    Details
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: A molecular mechanical force field for fluorinated ethylenes and propylenes is described. The field computes geometries, dipole moments, and energy differences between isomers and rotamers. Component analysis indicates that “classical” strains alone (skeletal, nonbonded, electrostatic) cannot account for energy relationships. The discussion is supplemented by a semiempirical quantum chemical comparison of cis- and trans-FCH=CHF and of gauche- and anti-FCH2CH2F.
    Additional Material: 4 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540010202
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  • 13
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    A theoretical approach to substituent effects.For previous articles in the series, see refs. 1 and 2. Interactions between directly bonded groups in the neutrals X—NH2, X—OH, and X—F and the anions X—NH- and X—O- (1980)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 1 (1980), S. 118-128 
    Details
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: Ab initio molecular orbital calculations have been carried out for the neutrals X—NH2, X—OH, and X—F and the anions X—NH- and X—O- with substituents X = Li, BeH, BH2, CH3, NH2, OH, and F. All structures have been fully optimized with the 4-31G basis set which is found to perform considerably better than the minimal STO-3G basis in predicting the lengths of strongly polar bonds. A quantitative analysis of interactions between the directly bonded groups, utilizing energy changes in hydrogenation reactions, is presented and rationalized with the aid of perturbation molecular orbital theory. Favorable interactions occur when electron-donor groups bond to electron-acceptor groups. This applies to both σ and π interactions, the relative importance of which depends on the particular substituents.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540010203
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  • 14
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    Conformational energy surfaces of triplet-state isomeric methyloxiranes (1980)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 1 (1980), S. 141-148 
    Details
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: A conformational study was carried out on the three ring-opened structures of triplet methyloxirane with a minimal Gaussian basis set, within the unrestricted Hartree-Fock framework. For the two structures energy surfaces E(θ1, θ2) were generated, where θ1 measures the methyl rotation and θ2 is associated with the torsion about the other C—C bond. For the third structure an energy hypersurface E(θ1, θ2, θ3) was generated, where energy was a function of methyl rotation θ1 and two nonequivalent C—O rotations θ2 and θ3. Analysis of the surfaces revealed the locations and relative energies of the critical points (minima, saddle points, and maxima). The overall stereochemical finding was that these ring-opened triplet C3H6O species possessed rather flexible structures.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540010206
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  • 15
    Electronic Resource
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    A theoretical study of paths for decomposition and rearrangement of dihydroxycarbene (1980)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 1 (1980), S. 158-166 
    Details
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: The transition states for fragmentation of dihydroxycarbene [C(OH)2] to H2 and CO2 and for the rearrangement of this carbene to formic acid were located by ab initio calculations. The relative energies of the transition states were determined at several levels of theory and the basis set dependence of the energies is discussed. At the best level of theory; using a basis set of double-zeta quality augmented by polarization functions and with the inclusion of extensive CI, we found that the transition state for fragmentation was considerably higher in energy than that for rearrangement. This finding is at variance with the predictions of the Woodward--Hoffmann rules because fragmentation represents an “allowed” reaction, whereas rearrangement is “forbidden.” In conformity with the Woodward-Hoffman rules, the transition state for rearrangement was found to be close in energy to H· + ·CO2H. The even higher energy of the transition state for concerted fragmentation to H2 and CO2 is attributed to the need for the latter fragment to remain substantially bent in order to permit H2 formation while maintaining a modicum of OH bonding. Difficulties in locating the transition state for concerted fragmentation are discussed and a new method for finding transition states is proposed.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540010208
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  • 16
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    Electronic Resource
    Gaussian basis sets for the fourth-row main group elements, In-Xe (1983)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 4 (1983), S. 181-186 
    Details
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: Gaussian basis sets, consisting of 15 s-type, 11 p-type, and 6 d-type functions, for the fourth-row main group elements, In-Xe, are presented. In order to compare these basis sets with larger ones, calculations have been performed in I2 and TeO2.
    Additional Material: 6 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540040210
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  • 17
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    Energetics and structure of the hydrated gaseous halide anionsThis work was suported by NSF grant No. CHE-7826623. (1983)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 4 (1983), S. 283-293 
    Details
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: Energetics and geometries for the hydrated gaseous halide anions have been computed from a simple model in which the molecular dipole of water was composed of two parts, one due to a lone pair on oxygen (60%) and the rest to formal charges on the nuclei. The calculations were made for both the symmetric and nonsymmetric structures. A variety of structures were used to compute potential energies and distances with up to six water molecules. The total energy consisted of a sum of electrostatic, polarization, dispersion, and repulsion terms. Various sets of repulsive potential parameters, ranging from those determined from molecular beam experiments to those determined using experimental ion-water distances or energies, have been employed to compute repulsive interaction energies. It was found that the range parameters play a significant role in deciding the magnitudes of the distances and energies, as the latter are most sensitive to them. It was also shown that with a simple correlation scheme the consistency of the experimental energies and distances can be tested separately without using repulsive potential parameters from other sources. It also suggests that a range of parameters can be used to compute repulsion energies. Despite the fact that the model is greatly simplified, the agreement of both the predicted ion-oxygen distances and energies with both experiment and other calculations is excellent. A detailed analysis of our calculation suggests that the negative ion clusters with one to three water molecules contain symmetric orientation of water molecules, while those with more than three may contain asymmetric orientations of water molecules or a mixture of both. From the log-log plots of hydration energies versus (R + radius of water molecule), we have proposed empirical expressions of the type ΔEn-1,n = 10·0x (R + 1.38)-y with both Pauling's and Ladd's radii for univalent ions with which stepwise hydration energies of the latter can be predicted if we know thier radii. The values predicted for the alkali cations are in excellent agreement with the experimental and theoretical values, indicating the consistency of the simple model.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540040302
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  • 18
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    Uracil-4-Hydroxyuracil tautomerism revisited (1983)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 4 (1983), S. 345-349 
    Details
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: The tautomerism of the uracil-4-hydroxyuracil system is examined with the 3-21G basis set and full geometry optimization using gradient techniques. Single-point calculations at the 6-31G level were also done and the results compared with the 2-pyridone-2-hydroxypyridine system. The best ΔE(taut) obtained in this work is 74.1 kJ/mol.
    Additional Material: 2 Tab.
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    URL: http://dx.doi.org/10.1002/jcc.540040309
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  • 19
    Electronic Resource
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    Masthead (1983)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 4 (1983) 
    Details
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540040101
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  • 20
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    An ab initio study of the relative stabilities of the isomers of CH2N2 and SiH2N2 (1983)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 4 (1983), S. 1-8 
    Details
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: Ab initio SCF calculations of the equilibrium geometries have been carried out on nine possible isomers of MH2N2, where M = C or Si, and compared with the results of MNDO calculations. The results for the carbon compounds are in good agreement with available experimental data, but in the case of the silicon compounds, the molecules are predicted to be unstable with respect to decomposition to SiH2 and N2. The inclusion of electron correlation at the MP3 level does not alter the order of the relative stabilities, although the importance of the correlation contribution varies substantially between the different isomers.
    Additional Material: 3 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540040102
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  • 21
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    Computer enumeration and generation of benzenoid hydrocarbons and identification of bay regions (1983)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 4 (1983), S. 23-32 
    Details
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: A computer-oriented algorithm is developed for enumerating and generating all rigorously planar benzenoid hydrocarbons. An additional algorithm is also developed for identification and enumeration of carcinogenic bay regions. The results are reported for undisrupted benzenoid structures up to ten fused rings. The reported numbers of isomeric benzenoids do not agree with the results in the literature, because other authors included in their considerations some polyhexes which are not strictly planar structures (e.g., helicenes) or which represent rings of hexagons (e.g., circulenes). The reported results for enumeration of bay regions fully agree with those of Balasubramanian et al.
    Additional Material: 10 Ill.
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    URL: http://dx.doi.org/10.1002/jcc.540040105
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  • 22
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    Digital emulation of analog computer techniques for the solution of kinetic systems (1983)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 4 (1983), S. 58-67 
    Details
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: A low-cost microcomputer and package of assembly language routines has been developed to emulate the structure and performance of a large analog computer. The advantages of the analog computer, as implemented in this scheme, include (1) a significant reduction in the programming effort involved in modeling complex dynamic systems and (2) the control of the simulation and model parameters in a completely interactive and flexible manner. The symbolic nomenclature and schematic representations involving devices, such as integrators, comparators, multipliers, and function generators, offers a powerful alternative to the more conventional numerical methods, that is, to provide very simply the solutions to large systems of differential equations. This approach invariably leads the user to a more thorough understanding of the dynamic character of the system. The technique is illustrated using a chemical kinetics example involving the simulation of laser-induced fluorescence. The results of this work have provided an assessment of a systematic error that occurs when using induced resonance fluorescence to measure OH concentrations in the troposphere of the earth.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540040110
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  • 23
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    The thioketone-enethiol tautomerism of aliphatic thiocarbonyls: An ab initio study (1983)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 4 (1983), S. 104-109 
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    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: Approximate minimum energy reaction paths have been calculated for two thioketone-enethiol tautomeric systems using an ab initio SCF-MO method. The calculations indicate nearly equal stabil ties of the isolated tautomers in both systems and an energy barrier of ca. 85 kcal/mol for their interconversion. This barrier is expected to be significantly lower in solution as a result of solvent-solute interactions.
    Additional Material: 5 Ill.
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    URL: http://dx.doi.org/10.1002/jcc.540040114
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  • 24
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    A study by molecular mechanics of the geometric isomers of benzene hexachloride, benzene tetrachloride, and naphthalene tetrachloride (1983)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 4 (1983), S. 114-122 
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    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: The MM2 molecular mechanics force field, as modified for halogens, is able to predict the structures, dipole moments, and energies of the isomers of benzene hexachloride. For benzene tetrachloride and naphthalene tetrachloride the field exaggerates the stability of conformers with axial chlorine, but gives satisfactory results if the field is modified to allow for interaction between electronegative substituents and the π electrons.
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    Announcement (1983)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 4 (1983), S. 124-124 
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    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540040118
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    Electronic structure of UH, UF, and their ions (1983)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 4 (1983), S. 127-135 
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    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: A relativistic effective core potential (REP) has been generated for the uranium atom and used in self-consistent-field calculations of the A states of UH, UF, and their ions. Energy curves were calculated at the base configuration level which ensures the dissociating atoms are described by Hartree-Fock wavefunctions. The electronic bonding of these molecules is found to be similar to that of comparable alkaline-earth hydrides and fluorides. The uranium 6p, 6d, and 5f orbitals retain their atomic character but the orbitals extend into the bonding region and are distorted by overlap repulsion and electrostatic effects. Nonetheless, the atomic energetic coupling determines that low energy states will have the maximum spin multiplicity and maximum orbital angular momentum projection consonant with the charge-transfer bonding.
    Additional Material: 4 Ill.
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    URL: http://dx.doi.org/10.1002/jcc.540040202
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    Computation of electron repulsion integrals using the rys quadrature method (1983)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 4 (1983), S. 154-157 
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    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: Following an earlier proposal to evaluate electron repulsion integrals over Gaussian basis functions by a numerical quadrature based on a set of orthogonal polynomials (Rys polynomials), \documentclass{article}\pagestyle{empty}\begin{document} $$ (\eta \eta \parallel \eta \eta) = 2(\rho/\pi)^{1/2} \sum\limits_{\alpha = 1, N} I_x(u_{\alpha})I_{y}(u_{\alpha}) I_z(u_{\alpha})W_{\alpha} $$ \end{document} a computational procedure is outlined for efficient evaluation of the two-dimensional integrals Ix, Iy, and Iz. Compact recurrence formulas for the integrals make the method particularly fitted to handle high-angular-momentum basis functions. The technique has been implemented in the HONDO molecular orbital program.
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    The use of CNDO/force and compliance constant methods in evaluating quadratic potential functions of carbonyl and formyl fluorides (1983)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 4 (1983), S. 175-180 
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    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: CNDO/Force and compliance constant methods were applied to define general quadratic potential functions for F2CO and HCOF. A satisfactory set of compliants was obtained by suitably scaling down the stretching and stretch-stretch elements of the initial force constant matrix, evaluated by the CNDO/force approach, followed by fitting the compliants to available experimental data.
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    A new treatment of the vibration-Rotation eigenvalue problem for a diatomic molecule (1983)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 4 (1983), S. 218-225 
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    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: The problem of the determination of the vibration-rotation eigenvalue in diatomic molecules is considered. An eigenvalue equation totally independent from the eigenfunction is written for any potential, analytical or numerical. This equation uses uniquely the vibration-rotation canonical functions; its resolution is reduced to that of a simple and classical numerical problem. Examples of numerical applications for analytical (Morse) and numerical potentials are presented. It is shown that the vibrational eigenvalues deduced from the eigenvalue equation are within 10-6 cm-1 of the exact values. Comparison with conventional methods are presented and discussed.
    Additional Material: 7 Tab.
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    URL: http://dx.doi.org/10.1002/jcc.540040212
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    Molecular symmetry. IV. The coupled perturbed Hartree-Fock methodThis work was supported by the Director, Office of Energy Research, Office of Basic Energy Sciences, Chemical Sciences Division of the U. S. Department of Energy under Contract No. DE-AC03-76SF00098 and by the National Science Foundation under Grant No. CHE-7721305. (1983)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 4 (1983), S. 234-240 
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    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: Symmetry methods employed in the ab initio polyatomic program HONDO are extended to the coupled perturbed Hartree-Fock (CPHF) formalism, a key step in the analytical computation of energy first derivatives for configuration interaction (CI) wavefunctions, and energy second derivatives for Hartree-Fock (HF) wavefunctions. One possible computational strategy is to construct Fock-like matrices for each nuclear coordinate in which the one- and two-electron integrals of the usual Fock matrix are replaced by the integral first derivatives. “Skeleton” matrices are constructed from the unique blocks of electron-repulsion integral derivatives. The correct matrices are generated by applying a symmetrization operator. The analysis is valid for many wavefunctions, including closed- or open-shell spin-restricted and spin-unrestricted HF wavefunctions. To illustrate the method, we compare the computer time required for setting up the coupled perturbed HF equations for eclipsed ethane using D3h symmetry point group and various subgroups of D3h. Computational times are roughly inversely proportional to the order of the point group.
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    Orbital photography (1983)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 4 (1983), S. 276-282 
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    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: A scheme is presented that enables photographic representation of the (two-dimensional) surfaces of (three-dimensional) molecular orbitals and electron density functions. The algorithm has been implemented by a program which is completely general and computationally efficient.
    Additional Material: 6 Ill.
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    URL: http://dx.doi.org/10.1002/jcc.540040219
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    Molecular mechanics studies of enthalpies of formation and strain energies of azoxyalkanes (1983)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 4 (1983), S. 308-312 
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    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: A force field has been developed, on the basis of available experimental and partial retention of diatomic differential overlap (PRDDO) data, to permit molecular mechanics calculations on azoxyalkanes. The calculated structures and enthalpies of formation are in fair agreement with experimental results. The calculated enthalpies of formation and strain energies are compared with the corresponding quantities for analogous azoalkanes.
    Additional Material: 7 Tab.
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    Theory of the radiative lifetime of the 3B1 state of SO2 (1983)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 4 (1983), S. 337-344 
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    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: Interchange and many-body perturbation theory are applied to the calculation of the radiative lifetime of the 3B1 state of SO2. The radiative lifetime of 3B1 SO2 is predicted to be 7.6 msec, in excellent agreement with the experimental collision-free phosphorescence lifetime. As a separate calculation, interchange perturbation theory is used to determine the radiative lifetime of the 1A1 state of CH2.
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    Energetics of the neighbor exclusion model of intercalation (1983)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 4 (1983), S. 333-336 
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    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: The nearest-neighbor exclusion model for intercalation was studied using an energetical approach. It was shown that creation of the intercalation site in the exclusion model corresponds to the same energetical destabilization of the structure as in the standard model of intercalation. The stability of the intercalation complex formed in the case of the exclusion model is lower by 68 kcal/mol as compared with the standard model, but geometrical structures of both complexes are very similar. The electrostatic molecular potential method was also used to further characterize the intercalation site formed within both models of intercalation.
    Additional Material: 4 Ill.
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    Nonrelativistic and quasirelativistic model potential calculations on AgH and Ag2 (1983)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 4 (1983), S. 350-361 
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    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: The major relativistic effects are included into the model potential (MP) method of Bonifacic and Huzinaga. The effects are incorporated on the level of Cowan and Griffin's relativistic Hartree-Fock (RHF) method. The model potential parameters are determined using the results of nonrelativistic Hartree-Fock (NHF) and RHF calculations. A new scheme of selection of the basis functions for use in atomic and molecular MP calculations is proposed. To obtain agreement with the Hartree-Fock calculations on AgH and Ag2, the 4p shell has to be included explicitly in the MP calculations. The explicit treatment of the 4p electrons and the resulting reduction of the core size are necessary in order to overcome difficulties with approximate representation of the large 4p-4d core-valence interactions on the MP level.
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    Isotope effects in molecular mechanics (MM2). Calculations deuterium compounds (1983)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 4 (1983), S. 399-403 
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    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: Parameters have been derived so as to enable the inclusion of deuterium in the MM2 molecular mechanics force field. Several compounds were studied and the results are compared with experiment. The results are never qualitatively wrong, but the accuracy ranges from excellent to only fair. They are quite good for hydrocarbons, but less so for ketones.
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    Three-electron bonds. III. Phosphorus and chlorine σ* radical cations (1983)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 4 (1983), S. 404-409 
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    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: The radical cations H3PPH3+⋅, H3PSH2+⋅, H3PClH+·, and HClClH+· have been studied by ab initio molecular-orbital theory. An increasing tendency to adopt trigonal bipyramidal (TBP) gemoetries is observed for the phosphorus radicals with sulfur and chlorine ligands. The three-electron bond dissociation energies are calculated to be between 7 and 31 kcal mol-1. The dependence of these bond energies on the ionization potentials for the neutral hydrides is illustrated, and the deformation of phosphorus σ* radicals towards TBP structures is discussed.
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    Computer-assisted pseudorotation analysis of five-membered rings by means of proton spin-spin coupling constants: Program PSEUROT (1983)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 4 (1983), S. 428-437 
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    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: A computer method for the calculation of the pseudorotational parameters in five-membered rings from vicinal proton spin-spin coupling constants is described. Some typical problems met in practice are discussed. Applications of the program in the conformational analysis of some substituted cyclopentanes are presented.
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    Ab initio study of catalyzed and uncatalyzed amide bond formation as a model for peptide bond formation: Ammonia-Glycine reactions (1983)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 4 (1983), S. 449-460 
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    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: As a model reaction for peptide and bond formation, the SN2 reactions between glycine and ammonia have been studied with and without amine catalysis: \documentclass{article}\pagestyle{empty}\begin{document}$${\rm NH}_3 + {\rm NH}_2 {\rm CH}_2 {\rm COOH} + ({\rm NH}_3 ) \to {\rm NH}_2 {\rm CH}_2 {\rm CONH}_2 + {\rm H}_2 {\rm O} + ({\rm NH}_3 )$$\end{document} using ab initio molecular-orbital methods. For each of the catalyzed and uncatalyzed reactions, two reaction mechanisms have been examined: a two-step and a concerted mechanism. The stationary points of each reaction, including intermediate and transition states, have been identified and free energies calculated for all geometry-optimized reaction species to determine the thermodynamics and kinetics of the reaction. The calculations demonstrate that a second ammonia molecule catalyzes amide bond formation, and that the two-step mechanism is more favorable than the concerted one for the catalyzed reaction, while for the uncatalyzed reaction both mechanisms are competitive.
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    The propagation of basis-set error and geometry optimization in ab initio calculations. II. Correlation between the balance of Gaussian basis sets and calculated molecular properties (1983)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 4 (1983), S. 482-487 
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    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: Basis-set balance parameters, defined in terms of various projections of an abstract force vector in the space spanned by the logarithms of orbital exponents, are evaluated for a sample of 100 Gaussian basis sets. These basis sets are taken from a random Gaussian distribution of bases, centered on the best energy, fully variational uniform quality (UQ) atomic orbital (AO) basis sets. With each basis geometry optimization has been carried out for model molecule dimethyl sulfoxide, the wavefunction of which molecule is exceptionally sensitive to basis-set errors. Correlations between the balance of basis sets and calculated molecular properties are analyzed.
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    URL: http://dx.doi.org/10.1002/jcc.540040405
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    A theoretical study of α-substituted isopropyl and cyclopropyl anions (1983)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 4 (1983), S. 513-523 
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    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: Ab initio molecular orbital theory has been used to probe the effect of the substituent X on the structures, strain energies, stabilization energies, inversion barriers, and proton affinities of carbanions CH3CX CH3- and cis-C3H4X-, where X = H, F, CN, and NC. All geometries have been optimized with a 3-21G basis set, and the parent anions (X = H) were also optimized with the same basis set with a diffuse function added (i.e. the 3-21 + G basis set). The anions, with the exception of the α-cyanoisopropyl anion, are pyramidal. The out-of-plane angle, α, for the pyramidal anions decreases in the order F 〉 H ≈ NC 〉 CN, and the barriers to inversion follow the same order with the cyclopropyl anions consistently having higher barriers than the isopropyl anions. The substituents strongly stabilize the anions with the stabilization energy following the order CN 〉 NC 〉 F. The cyano group slightly reduces the strain energy of cyclopropane, but the isocyano and fluoro substituents are weakly and strongly destabilizing, respectively. The pyramidal cyclopropyl anions are less strained than the cyclopropanes except when the substituent is a cyano group where the strain energies are reversed but are very similar. The planar anions all have higher strain energies than the cyclopropanes.
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    Faster finite-difference calculations of molecular properties (1983)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 4 (1983), S. 552-555 
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    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: A very simple yet effective device for reducing the number of self-consistent-field (SCF) cycles in central finite-difference calculations of molecular properties is presented. The efficiency of this is demonstrated by MINDO/2 calculations of the force constants of a variety of molecules. The device consists of using information about the wavefunction at two values of a perturbation parameter to provide an estimate of the wavefunction at a third. This estimate is then used as an initial guess in an SCF procedure. The underlying theory is discussed and applications to other problems are suggested.
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    Ab initio evaluation of absorption and emission transitions for molecular solutes, including separate consideration of orientational and inductive solvent effects (1983)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 4 (1983), S. 567-577 
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    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: An ab initio computation procedure to obtain electronic transition wave numbers in solution is presented and discussed. The continuum description of the bulk solvent is adopted, and solute-solvent interaction is reduced to a closed-form interaction operator added to the solute Hamiltonian. The resulting Schrödinger equations are solved variationally. No limitations are imposed on the shape of the solvent cavity or on the level of accuracy of the ab initio procedure.
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    Molecular mechanics, by Ulrich Burkert and Norman L. Allinger, published by the American Chemical Society, 1982. 339 pages, $64.95. (1983)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 4 (1983), S. 605-605 
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    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
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    URL: http://dx.doi.org/10.1002/jcc.540040420
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    MNDO calculations of proton and methyl-and ethyl-cation affinities of neutral carbon, nitrogen, and oxygen bases (1983)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 4 (1983), S. 594-604 
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    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: Proton affinities (PA) of 80 neutral bases were calculated using the semiempirical molecular orbital procedure MNDO. These were compared with the corresponding experimental and, where available, ab initio STO-3G and 4-31G data. For the 12 bases studied which led to ions which were not hyperconjugatively stabilized, the mean absolute error between the calculated and experimental values was 7.2 kcal mol-1. However, a plot of these data revealed a clear tendency of MNDO to underestimate the PAs of the more basic molecules. Where hyperconjugative stabilization of the ion was possible, the calculated PAS were underestimated by a further 7-10 kcal mol-1 for each attached alkyl group. Calculated and observed methyl-and ethyl-cation affinities were compared for 18 bases with qualitatively similar results.
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    Masthead (1980)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 1 (1980) 
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    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
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    URL: http://dx.doi.org/10.1002/jcc.540010101
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    Orbital topology. II. Orbital mapping of unsymmetrical molecules. A survey of the thermal isomerizations of dewar isomers of isoelectronically substituted benzenes, cyclopentadienes, and cyclopentadienyl ions (1980)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 1 (1980), S. 21-29 
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    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: Orbital mapping analysis, based on EHT and CNDO/2 semiempirical molecular orbitals, has been used to survey the thermal, disrotatory, ring-opening isomerizations of bicyclo[2.2.0]hexa-2,5-dienes (Dewar benzenes), bicyclo[2.1.0]pent-2-enes, and bicyclo[2.1.0]pent-2-en-5-yl ions to their planar isomers. Results indicate that isoelectronic substitution (CH replaced by C-, O+, N, NH+, etc.) in the molecular framework may favor allowed thermal reactions in some cases, in contrast to the disallowed reaction predicted for the parent hydrocarbons.
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    Metal-metal bond energies in Mo2, Mo2Cl84-, and Mo2(O2CH)4 (1980)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 1 (1980), S. 59-63 
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    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: Previous attempts to determine the strengths of multiple metal-metal bonds are reviewed. Estimates of 73 and 97 kcal/mole for the Mo—Mo bond energies in Mo2Cl84- and Mo2(O2CH)4, respectively, are obtained by combining the known experimental bond energy in Mo2 (96.5 ± 5 kcal/mole) with the results of SCF-Xα-SW calculations on Mo2, Mo2Cl84-, and Mo2(O2CH)4. Possible errors in the estimates are discussed. It is noted that the quadruple bonds in the complexes are predicted stronger per component than the sextuple bond in the diatomic.
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    URL: http://dx.doi.org/10.1002/jcc.540010107
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    A pseudopotential SCF-MO study of Te42+ (1980)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 1 (1980), S. 64-68 
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    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: A recently developed ab initio pseudopotential molecular orbital approach was applied to the Te42+ ion, a system outside the practical reach of conventional all-electron treatments. Computations were carried out with a minimal STO-4G basis set. Results account reasonably well for the observed optical absorption spectrum and suggest the origin of a hitherto unassigned weak band. Ground-state properties, which included the structure, force field, and vibrational frequencies, were also investigated. Treated as a free, gas-phase ion, tetratellurium (II) yielded a bond length 0.05 Å shorter than the experimental value for the ion in a crystal lattice. Placement of static, point-charge counterions in the Te42+ coordination sphere increased the bond length to a value 0.005 Å longer than derived by experiment. Calculations on neutral, cyclic Te4 provided a theoretical single-bond reference length 0.09 Å longer than that obtained for the ion in a counterion environment. Comparisons between observed and calculated frequencies suggest an assignment of the vibrational spectrum different from the provisional assignment in the literature.
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    Integrated spatial electron populations in molecules: Application to simple molecules (1980)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 1 (1980), S. 81-87 
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    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: The electron projection function P(x, z) = ∫ ρ(x, y, z) dy is used to evaluate charge transfer and covalency in two series of molecules, LiX and CH3X (X = Li, BeH, BH2, CH3, NH2, OH, and F), with wavefunctions derived from STO-3G, 4-31G, and, in some cases, 6-31* ab initio calculations. The precision of the method and comparison with Mulliken populations analysis are described. Particular attention is given to CH3Li which by our criteria is wholly ionic.
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    Isomeric structures of protonated ozone: A theoretical study (1980)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 1 (1980), S. 94-98 
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    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: Ab initio molecular orbital calculations have been used to determine the structure of protonated ozone. Four stable minima were found on the O3H+ singlet potential energy surface. Three forms correspond to ozone protonated at the central oxygen (C2v) or at the terminal oxygen (two Cs isomers, E and Z). The fourth isomer (Cs) is a derivative of trioxirane. The most stable structure is the planar E form I. The proton affinity of ozone (to give I) is given as 123.6 kcal/mole (MP2/6-31G*//4-31G). The energy difference between I and protonated trioxirane VI is greater than that between ozone and trioxirane.
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    The application of molecular mechanics to the structures of carbohydrates (1980)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 1 (1980), S. 99-109 
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    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: A study is reported of the accuracy with which the geometries of pyranose and methyl pyranoside molecules are predicted by molecular mechanics. Calculations of the conformational energies of the model compounds dihydroxymethane, methoxymethanol, and dimethoxymethane, made with the program MMI, produced results that compare well with previous ab initio molecular orbital calculations. This indicates that MMI gives a satisfactory account of the energetic and conformational aspects of the anomeric effect, a conclusion further supported by calculations on 2-methoxytetrahydropyran. The prediction of the observed preferred conformations of the primary alcohol group in aldohexopyranoses appears to be less satisfactory. MMI-CARB, a version of MMI with changes in some of the equilibrium C—O bond lengths of the program, has been used to calculate the geometries of 13 pyranose and methyl pyranoside molecules, the crystal structures of which have been studied by neutron diffraction. When the C—C—O—H torsion angles are constrained to approximately the values observed in the crystal structures, good agreement is obtained between the theoretical and experimental molecular geometries. The rms deviation for C—C and C—O bonds, excluding those significantly affected by thermal motion in the crystal structure determinations, is 0.005 Å. Corresponding figures for the valence angles that do not involve hydrogen atoms and for the ring torsion angles are 1.2° and 2.0°, respectively. The Cremer and Pople puckering parameters for the pyranose rings are reproduced within 0.026 Å in Q and 5.4° in θ.
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    Graph theoretical characterization and computer generation of certain carcinogenic benzenoid hydrocarbons and identification of bay regions (1980)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 1 (1980), S. 149-157 
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    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: An algorithm is developed for generating and characterizing carcinogenic catacondensed benzenoid hydrocarbons. The bay regions in these structures are identified by a technique that we developed at Johns Hopkins. Using the three-digit code proposed by Balaban, and the concept of ring adjacency matrix expounded here, we generate catacondensed benzenoid hydrocarbons in the computer and identify the number of potentially carcinogenic bay regions in each of them. The results of computer generation agree with the combinatorial enumeration of Harary and Read. All structures containing up to five rings and some with six rings and the number of bay regions in these are presented. Computer results for the structures and bay regions of all seven-, eight-, and nine-membered unbranched catacondensed benzenoid hydrocarbons and the number of bays are available from the authors.
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    The structure and energies of some unsaturated four-membered ring carbocycles (1980)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 1 (1980), S. 30-35 
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    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: A number of cyclobutane derivatives containing one or more double bonds in endo- or exocyclic positions have been studied by the molecular mechanics method within the context of the MM2 force field. Generally speaking, the structures and energies of these compounds are well calculated in cases in which they are known experimentally and are predicted in others. Examples are shown of the use of the moments of inertia of molecules, which are known from microwave studies, in conjunction with molecular mechanics calculations to yield better structures than could be obtained by either method alone. Compounds examined include cyclobutene, methylenecyclobutane, Dewar benzene, and related compounds.
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    A simplex optimized INDO calculation of 13C chemical shifts in hydrocarbons (1980)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 1 (1980), S. 36-45 
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    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: The variable-size simplex optimization method is used to reparametrize the I + A and β parameters of an INDO approximation to the perturbed Hartree-Fock calculation of 13C chemical shifts in hydrocarbons. The absolute shifts for 39 nuclei in a set of molecules containing up to four carbons are reproduced within a standard error of 9.9 ppm for an unconstrained optimization and to a standard error of 10.0 ppm for an optimization constrained to yield gross atomic charges in agreement with double-zeta ab initio calculations.
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    Orbital topology. I. A basic topological model for chemical systems, an orbital mapping technique, and analyses of model, thermal electrocyclic reactionsThis article is based in part on D. R. Kelsey's Ph.D. Thesis, California Institute of Technology, Pasadena, California, October 31, 1972; a brief discussion of these concepts and results has been presented at the American Chemical Society's 172nd National Meeting, San Francisco, September 2, 1976, abstract ORGN 199. (1980)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 1 (1980), S. 3-20 
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    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: A topological model which provides a unifying framework for chemical reactions and molecular structure is proposed. Such basic concepts as overlap, orthogonality, reaction continuity, reaction reversibility, and orbital correspondence are incorporated into the model in a logical fashion. A chemical reaction pathway is regarded as a function that transforms a reactant topological space into its equivalent product space. The unique character usually ascribed to reactants, products, and their wavefunctions is superfluous. The model also allows considerable approximation of the wavefunctions and the reaction pathway without affecting the overall result. A simple orbital mapping technique consistent with the model which traces the transformation of orbitals using intermolecular overlaps of the orbitals is also proposed. The suitability of a given pathway (“allowed” or “forbidden”) can be deduced explicitly without invoking symmetry (or other) rules and without resorting to detailed calculation of reaction energy surfaces. The validity of the mapping procedure has been confirmed by several thermal electrocyclic reactions: the ring-opening isomerizations of substituted cyclopropyl cations, cyclopropyl anion, cyclopropanone, cyclobutene, benzocyclobutene, Dewar benzenes, and 1,3-cyclohexadiene. Orbital mapping with EHT and CNDO/2 MOs correctly predicts the reaction stereochemistry (conrotatory or disrotatory) in every case.
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    Molecular charge distribution and chemical binding in five-membered heterocycles. I (1980)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 1 (1980), S. 348-357 
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    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: Electron density maps for the heterocycles thiophene, furan, and pyrrole are determined from ab initio 4-31G wavefunctions. The charge distributions in these molecules are analyzed in terms of the total molecular density and difference density maps and their profiles. The atomiclike core, especially the L core of sulfur, is found to play an important role, via its polarization and interaction, in determining the extent and direction of valence density transfer from the carbon to the heteroatom. The changes in the charge distributions that occur in the immediate vicinity of the heteroatoms and the relation of density quantities to binding and antibinding characteristics are discussed. The quantum topological features of the molecular charge distributions of the three heterocycles are analyzed and discussed and the different bonding situations, e.g., ring strain, ionic and covalent binding, etc., are compared in a model-independent way.
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    Prediction of the crystal structure of a cyclic tetrapeptide (1980)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 1 (1980), S. 368-372 
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    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: Prediction of the known crystal structure of cyclic-L-Ser(O-t-Bu)-β-Ala-Gly-L-β-Asp(OMe) has been attempted by establishing the low-energy conformations of the isolated molecule by conformational analysis, and then regarding each of these as a rigid molecule, by establishing the favorable crystal packing arrangements by molecular packing analysis. The theoretical model closest to the observed structure was one of the lowest-energy solutions and was recognized as essentially correct by reference to the x-ray data. The limitations of the model follow from the fact that the side chain conformations are somewhat affected by packing interactions.
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    Quantum chemical investigations of charge transfer interactions in relation to the electronic theory of cancer. IV. The interaction of formamide and the enol tautomers of several glyoxals (1980)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 1 (1980), S. 400-406 
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    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: The results of ab initio “supermolecule” calculations of the charge transfer between formamide and the enol forms of methylglyoxal, ethylglyoxal, dimethylglyoxal, and propenylglyoxal are compared for several different conformations of the constituent molecules. The enols were found to be poorer electron acceptors than their respective keto isomers.
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    INDO-Type calculations on the ground state and various ionic states of transition metal tricarbonylsPart 10 in the series “Electronic Structure of Organometallic Compounds.” For Part 9, see ref. 1. (1980)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 1 (1980), S. 407-416 
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    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: By means of the ΔSCF and transition operator (TO) methods based on a recently developed INDO extension to the first transition metal series, the first ionization potentials of benzene - chromium tricarbonyl (I), cyclopentadienyl manganese tricarbonyl (II), the iron - tricarbonyl complexes with trimethylenemethane (III), and cyclobutadiene (IV) have been calculated and compared with experimental data. It is shown that the electronic structure of I to IV can be rationalized by Hoffmann's fragment approach in both the ground state and the cationic hole states. Within the series I - IV there are remarkable energy differences in the ground state for MOs derived from the 1a1 and 1e orbitals of the M(CO)3 fragment. The observation that only one band is associated with the ionization events from MOs predominantly localized at the metal site is traced back to large relaxation effects. In the cationic hole states the split of the M(CO)3 fragment orbitals 1a1 and 1e is minute in all four compounds.
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    An ab initio study of the geometry, harmonic and anharmonic force fields, and fundamental vibrational frequencies of cis- and trans- thiolformic acid (1980)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 1 (1980), S. 167-177 
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    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: The geometry, harmonic and anharmonic force fields, and fundamental vibrational frequencies of cis- and trans-thiolformic acid are studied ab initio in the 4-31G basis set. An extensive comparison is made between changes in diagonal and off-diagonal quadratic and cubic force constants and diagonal stretching quartic constants in going from the chain to the ring structure in thiolformic acid and formic acid. The changes in the force constants are indicative of a much weaker interaction in the trans conformer between S—H and O=C, compared with O-H and O=C, in keeping with the weaker hydrogenbonding property of the S—H group in general.
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    The barrier to internal rotation in Ge2H6 (1980)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 1 (1980), S. 185-188 
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    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: High-quality SCF-MO calculations yield a barrier to internal rotation of 1.70 kJ mole-1 for Ge2H6. A new contraction scheme is reported for Dunning's larger Ge basis set. Geometry optimization, although carried out, is unimportant in this particular calculation. Wavefunctions and properties are reported for GeH4 and the staggered and eclipsed conformers of Ge2H6. The magnitude of the calculated barrier is more physically reasonable than those deduced from experimental data. Comparisons are made across the two series X2H6 and CH3XH3.
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    A theoretical comparison of cationic and anionic homoaromaticity: Reinforcement of cationic homoaromaticity by σ-nonclassical effects (1980)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 1 (1980), S. 189-191 
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    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: A MINDO/3 study of homoaromaticity in the 3-cyclobutenyl cation and the Mobius 3-cyclobutenyl anion has been used to evaluate cationic and anionic homoaromaticity quantitatively. π Homodelocalization energies of the two are found equal in isostructural planar comparisons. In planar optimized structures, the homodelocalization energy of the cation is slightly (about 4 kcal) greater than that of the anion, a consequence of the greater 1,3 distance in the latter. Full optimization produces a highly puckered and further stabilized cation, but engenders no change in the Mobius anion. The total stabilization of the cation relative to the anion is 13 kcal, in accord with the generalization that cationic homoaromaticity is more potent than the anionic variety. The fully optimized cation is revealed to actually have a much smaller π homodelocalization energy than the optimized anion, in contrast to the order of overall stabilities. σ-Nonclassical effects, which are stabilizing in the cation but destabilizing in the Mobius anion, provide the rationale for the above.
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    Applications of molecular mechanics calculations in carbohydrate chemistry. I. Conformational and constitutional equilibria of tetraoxabicyclo[4.4.0]- and -[5.3.0] decanes, bicyclic diacetals of alditols (1980)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 1 (1980), S. 192-198 
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    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: The energies of various conformations have been calculated by molecular mechanics for cis and trans isomers of 2,4,7,9-tetraoxabicyclo[4.4.0] decane and 3,5,8,10-tetraoxabicyclo[5.3.0]decane and their methyl derivatives. These molecules are models for reaction products from formaldehyde and the tetrols, pentitols, and hexitols. The conformational equilibria were analyzed for the cis-bicyclo [4.4.0] and cis-bicyclo[5.3.0] systems and compared with available experimental data. The thermodynamic stability of bicyclo[4.4.0] products was found to be higher than that of bicyclo[5.3.0] derivatives in the gas phase in every case studied. Discrepancies with experimental data that exist in a few cases can be ascribed to solvent effects.
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    Koopmans' theorem ionization potentials of methyl and silyl halides, chalcogenides, amines, and phosphines: An ab InitioSCF study (1983)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 4 (1983), S. 9-14 
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    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: Koopmans' theorem ionization potentials have been calculated for a series of hydrides, methyls, and silyls HnX, (CH3)nX, and (SiH3)nX (X = F, Cl, n = 1; X = O, S, n = 2; X = N, P, n = 3), together with some mixed species (MH3)nXH3-n (X = N, P; M = C, Si) using ab initio SCF methods. The calculated values give excellent agreement with experimental values without the inclusion of d functions. For the chlorides, HCl, CH3Cl, and SiH3Cl, the values vary rather little over a wide range of basis sets, and are unaffected by the inclusion of d functions.
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    Restricted Hartree-Fock approximation. II. Computational aspects of the direct minimization procedure (1983)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 4 (1983), S. 41-47 
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    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: A RHF energy minimization procedure based on the treatment outlined in Part I of this series of articles is presented. Test calculations performed on several closed- and open-shell systems show that the present procedure is definitely superior to the conventional SCF methods. In particular, the convergence of this procedure is ensured, the rate of convergency is high, and the computational cost of each cycle is low.
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    Ab initio studies on calicene (1983)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 4 (1983), S. 53-57 
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    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: Optimum geometries of planar and 90°-twisted C2v calicene are calculated with single-configuration STO-3G and 3-21-G wavefunctions. The barrier to ring-ring rotation is computed. Bond alternation is pronounced in the planar form and decreases in the twisted form, while dipolar character increases on twisting.
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    Comparison of RHF, NDDO, and MOM molecular one-electron expectation values calculated using weighted and unweighted STO-NG (ω) basis functions (1983)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 4 (1983), S. 48-52 
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    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: The effect of basis functions on molecular one-electron property expectation values calculated by approximate methods is examined using weighted and unweighted least-squares Gaussian-type orbital function expansions of Slater-type orbital functions.
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    Ab initio studies of a proposed mechanism for N-Nitrosamine formation (1983)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 4 (1983), S. 68-72 
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    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: The geometry of a proposed intermediate (α-dialkylamino nitrite ester) of N-nitrosamine synthesis from nitrites is studied by ab initio SCF methods. The energy of a zwitterion is calculated and found to be high.
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    Ground states of molecules. 56. See Part 55 in this series: M. J. S. D. Dewar and S. Olivella, J. Am. Chem. Soc., 101, 4958 (1979).MNDO calculations for molecules containing sulfur (1983)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 4 (1983), S. 84-103 
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    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: MNDO has been extended to sulfur, but without inclusion of 3d AOs. Calculations are reported for heats of formation, geometries, dipole moments, and ionization energies of a variety of sulfur-containing molecules. The average discrepancy between calculated and observed heats of formation is larger than for compounds of other elements, a difference probably due, at least partly, to the lower accuracy of the thermochemical data for sulfur compounds. The calculated dipole moments agree well with experiment as do the calculated ionization energies, except for those corresponding to ionization from sulfur “lone-pair” orbitals which are too high by ca. 1 eV, probably as a result of the neglect in NDDO of interactions between inner and valence shell orbitals. As in the case of other third-period elements, the calculated heats of formation of compounds of sulfur in its higher valence states (SIV, SVI) were too positive by large amounts, due presumably to the neglect of 3d AOs.
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    Progress in theoretical organic chemistry, volume 3, L. Radom et al. Elsevier, New York, 1982. Price: $103 (1983)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 4 (1983), S. 123-123 
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    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
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    URL: http://dx.doi.org/10.1002/jcc.540040117
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    Masthead (1983)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 4 (1983) 
    Details
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
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    URL: http://dx.doi.org/10.1002/jcc.540040201
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    Standard deviation in reduced errors (SDRE): A criterion to assess the relative overall quality of approximate wavefunctions (1983)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 4 (1983), S. 150-153 
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    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: The standard deviation in reduced errors (SDRE) quantitatively measures the similarity between an approximate and exact wavefunction. It is the Euclidean distance between the vector of the one-electron property expectation values calculated using the approximate and exact expectation values.
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    Dipole polarizability derivatives calculated by the Kirkwood method (1983)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 4 (1983), S. 170-174 
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    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: Derivatives, with respect to the symmetry coordinates, of the components of the dipole polarizabilities of HF, H2O, and CH4 are calculated using the Kirkwood method and a generalization of that method. The results for the bond-stretching derivatives are in reasonable agreement with those found by finite field calculations; those for angle changes are of the correct sign, but their magnitudes are in poor agreement with the finite field ones. The results are also analyzed using a four-parameter bond polarizability model.
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    Properties of excited states of aromatic rings containing nitrogen (1983)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 4 (1983), S. 410-418 
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    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: Quantum chemical calculations with the semiempirical molecular orbital (MO) method SINDO1 were performed on excited states of the following five- and six-membered heterocycles containing nitrogen: imidazol, pyrazol, pyridine, pyridazine, pyrimidine, pyrazine, and s-triazine. The geometries and adiabatic excitation energies of T1, S1, S2 were calculated. We also present charges, bond orders, and dipole moments. Consequences of these results for UV spectroscopic data are discussed.
    Additional Material: 7 Ill.
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    Masthead (1983)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 4 (1983) 
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    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
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    URL: http://dx.doi.org/10.1002/jcc.540040401
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  • 77
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    Theoretical conformational analysis of the Gramicidin a transmembrane channel. I. Helix sense and energetics of head-to-head dimerization (1983)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 4 (1983), S. 461-469 
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    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: Conformational energy calculations are presented for the head-to-head dimerized β helices for Gramicidin A transmembrane channel structures. The calculations take into account both left- and right-handed β helices, and various side-chain conformations. The energetics of the dimerization is studied by considering various docking geometries. It is concluded from these vacuum-energy calculations that the lowest energy conformation for the channel dimer is that comprised of left-handed β helices.
    Additional Material: 8 Ill.
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    Properties of strong hydrogen-bonded systems. II. Ab initioSCF-MO study of the hydrogen bond between nitric acid and ammonia (1980)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 1 (1980), S. 417-419 
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    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: The hydrogen-bonded complex between nitric acid and ammonia molecules has been studied by the ab initio molecular orbital method using the 4-31G basis set. The calculated interaction energy for the complex (ΔE = -91.4 kJ mole-1) indicates that one is dealing with the strongest “nonionic” H-bonded complex considered hitherto by theoretical methods. Other properties of the hydrogen-bonded complex such as geometrical parameters, dipole moment, amount of charge transfer, and stretching force constants of the O—H and (OH)… N bonds are calculated and discussed.
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    Substituent effects on the charge density in the formyl group (1983)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 4 (1983), S. 15-22 
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    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: SCF wavefunctions with similar extended Gaussian bases for the series HCOX with X = H, OH (syn and anti), NH2, CN, and F yield closely similar charge deformation density maps in the formyl region of all six molecules. The differences, measured by moments of partitioned atomic deformation densities, correlate almost linearly with the Hammett substituent parameters σI and σR of the several substituents X. However, systematic deviations, especially in the carbon fragment, suggest the need for modified values of the inductive parameters σI for the correlation of these molecular charge densities.
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    Restricted Hartree-Fock approximation. I. Techniques for the energy minimization (1983)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 4 (1983), S. 33-40 
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    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: We present a new procedure for direct minimization of the RHF energy, which presents advantages over SCF methods with respect to convergence rate and computational cost. In this procedure we combine several techniques with the aim of obtaining best directions and step lengths for the iterative search for a minimum of the energy. In this article we develop the theory. Therefore, we analyze the variational function; we present a short description of the minimization techniques and we discuss in detail the way in which they are to be used. The computational aspects of the procedure will be treated in the following article.
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    Symmetry properties of chemical graphs. V. Internal rotation in XY⋅3XY⋅2XY3 (1983)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 4 (1983), S. 73-83 
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    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: Structures XY⋅3XY⋅2XY3 of symmetry C2v (of which propane is an example) are examined and the rearrangement due to the internal rotation of the end groups XY3 studied. The isomerization graph is constructed, various forms of which are displayed and the symmetry of which has been determined. The order of the group is 72. There are nine prime (irreducible) representations (4A + E + 4G) with the following partitioning of the elements into classes: 1, 42, 62, 9, 122, 18. When the mechanism for rearrangement is generalized to include enantiomers, a duplex graph is produced with the order of the group 144 which is isomorphic to the group S2(S3,S2) (generalized wreath product of the symmetric group S2 and S3). The corresponding graph has been constructed and displayed in one of more symmetrical forms. Isomorphism of groups of order 144 is discussed and a procedure is outlined in which correspondence between distinctive combinatorial objects is established by inducing permutations of m elements from available permutations of n elements. The scheme is based on selection of suitable graph invariants in one system and their labeling as m objects which form the basis for representation of the symmetry for the other system.
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    A fast algorithm for calculation of the distance matrix of a molecule (1983)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 4 (1983), S. 110-113 
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    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: A rapid method is described for calculating the number of bonds on the shortest path between each two pairs of atoms of a molecule.
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    URL: http://dx.doi.org/10.1002/jcc.540040115
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    On the general transformation from molecular geometric parameters to cartesian coordinates (1983)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 4 (1983), S. 136-141 
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    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: This article presents a general method and accurate algorithm for calculating the Cartesian coordinates (xa, ya, za) from an arbitrary triple of distances r(a,i), angles, θ(a,j,k), or dihedral angles φ(a,l,m,n), specifying the position of the nucleus a relative to nuclei i,⃜, n with known Cartesian coordinates. There is a brief discussion of the requirements on the 3N-6 geometric parameters in order for them to determine the shape of an N-atomic molecule.
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    URL: http://dx.doi.org/10.1002/jcc.540040203
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    Divinylketone: Conformational preferences. Molecular geometry and vibrational force field in the ground state (1983)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 4 (1983), S. 142-149 
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    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: The conformational preferences of the molecule 1,4-pentadien-3-one (divinylketone) have been studied by ab initio molecular orbital calculations and discussed in terms of interaction between molecular fragments. The calculations predict a molecular ground state having a fully coplanar s-cis, s-cis conformation. In addition, we find three other structures that represent local minima on the energy surface. These are a fully coplanar s-cis, s-trans form, and two nonplanar s-trans, s-trans forms having symmetries C2 and C1h, respectively. The energies of these forms relative to the ground state are 7.5, 19.2, and 35.9 kJ/mol, respectively. The coplanar s-trans, s-trans form represents a saddle point on the energy surface. All conformers and the saddle point have been completely geometry optimized by the gradient technique. For the ground state a complete in-plane harmonic force field has been evaluated.
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    Ground states of molecules. 53.For part 52, see ref. 1.MNDO calculations for molecules containing chlorine (1983)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 4 (1983), S. 158-169 
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    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: MNDO calculations of heats of formation, dipole moments, ionization potentials, and structures are reported for a wide range of compounds containing chlorine in its characteristic valence state (ClI) and one or more of the elements H, B, Be, C, N, O, and F. The calculated errors in the heats of formation and the dipole moments are not significantly greater than those previously reported for compounds containing no chlorine. First vertical ionization potentials were on average 0.95 eV too high. The ordering of higher cationic states was found to be correct, even for species such as Cl2O, Cl2, and HOCl, where ab initio-Koopmans' theorem calculations predict the incorrect ordering. The calculated energies and geometries of compounds such as CIF3 are qualitatively incorrect, probably because of the lack of 3d atomic orbitals in the orbital basis set.
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    CHARMM: A program for macromolecular energy, minimization, and dynamics calculationsSupported in part by grants from the National Science Foundation and the National Institutes of Health. (1983)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 4 (1983), S. 187-217 
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    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: CHARMM (Chemistry at HARvard Macromolecular Mechanics) is a highly flexible computer program which uses empirical energy functions to model macromolecular systems. The program can read or model build structures, energy minimize them by first- or second-derivative techniques, perform a normal mode or molecular dynamics simulation, and analyze the structural, equilibrium, and dynamic properties determined in these calculations. The operations that CHARMM can perform are described, and some implementation details are given. A set of parameters for the empirical energy function and a sample run are included.
    Additional Material: 4 Ill.
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    URL: http://dx.doi.org/10.1002/jcc.540040211
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    Molecular orbital theory of the properties of inorganic and organometallic compounds. 3. STO-3G basis sets for first- and second-row transition metals (1983)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 4 (1983), S. 241-251 
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    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: STO-3G minimal basis sets for first- and second-row transition metals have been formulated and applied to the calculation of equilibrium geometries for a variety of inorganic systems, metal carbonyls, and organometallic compounds. While the overall level of agreement with experiment is not as good as that previously noted for main-group compounds, most trends and many subtle features in geometries are reproduced.
    Additional Material: 8 Tab.
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    Electronic optical activity of (-)-α-phellandrene (1983)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 4 (1983), S. 260-266 
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    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: Molecular orbital computations on the sign and magnitude of the Cotton effect of (-)-α-phellandrene (a conjugated diene) and the separate twisted butadiene chromophore were performed using configuration interaction (CI) and the random phase approximation (RPA) methods with a standard minimal basis set of STO/3G orbitals. The relative contributions to the rotatory strength of (-)-α-phellandrene which arise from a twist in the diene unit, the allylic axial bond, and nonplanarity of either one or both of the C=C double bonds were determined by examining various molecular geometries. This theoretical study confirms that the allylic axial substituent/bond provides the largest contribution to the longwavelength Cotton effect. It is found that the rotatory strength arising from distortion of the planar geometry of the double bonds tends to cancel the rotatory strength arising from the sense of twist of the diene unit. The computed energies suggest that molecular geometries where the trisubstituted bond is kept planar, and where twisting is allowed about the cis double bond, may be favored over geometries where torsion is allowed about both double bonds.
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    A technique for determining the symmetry properties of molecular graphs (1983)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 4 (1983), S. 267-275 
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    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: A procedure has been devised to determine the automorphism partition and the automorphism group for nondirected graphs. The general approach is to reveal the permutational symmetry by means of its systematic destruction. Symmetry decomposition pathways are created by numerically weighting specific series of vertices. Each pathway leads to a discrete ordered vector. Each pair of pathways that match reveals an element of the automorphism group. Results are presented for two molecular graphs. Further potential applications of this approach to problems of isomorphism, canonical labeling, and structural indexing are discussed.
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    Computer generation of the symmetry elements of nonrigid molecules (1983)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 4 (1983), S. 302-307 
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    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: Algorithms and computer programs are developed for generating the symmetry elements of nonrigid molecules. These programs are based on the wreath product formalism for the symmetry groups of nonrigid molecules developed by the present author. Several examples are given to illustrate the procedures. Applications to weakly bound van der Waal complexes synthesized by supersonic beam expansion are also presented.
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    Molecular mechanics with an array processor (1983)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 4 (1983), S. 313-332 
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    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: Computer simulation of the mechanics of molecular systems is a popular and powerful method for understanding chemical processes. The complexity of modeled chemical systems has advanced from hard spheres and rare gases to liquid solutions and biomolecules. Such simulations are computationally intensive and thus are limited by the speed of available computers. This article describes the use of specialized hardware, a high-speed floating-point array processor (AP), to dramatically speed up molecular mechanics, in other words molecular dynamics, Monte Carlo, and energy-minimization calculations. Although the array processor is a cost effective solution for computationally intensive problems in terms of hardware (full-time AP usage is equivalent to 2-8 h/day of Cray-1 time), its full speed comes at the expense of programming in a relatively difficult parallel assembly language. Since the architecture of the machine is dramatically different from conventional computers and utilizing its fast speed necessitates using this architecture on the assembly language level, the proper design and implementation of algorithms is critical. The molecular mechanics software design discussed here, consisting of 12,000 lines of C and 7000 lines of AP assembly language code, is quite general and has been used to study systems ranging from rare gases to biomolecules. This implementation yields effective speeds approximately 35 times faster than a dedicated DEC VAX 11/780 computer with floating-point accelerator and optimized VMS FORTRAN, thus allowing simulations to be run in one and a half weeks on the AP which would require a year of dedicated VAX time. The flexibility of the UNIX operating system, whose source code is accessible and can be modified to optimize performance, combined with the modern features of the C language, have made this implementation much easier by providing a convenient and powerful environment in which to imbed the hand-coded AP assembly language modules. Applications to date range from the molecular-dynamic calculation of infrared, Raman, and electronic spectra in gas and liquid solutions to the calculation of thermodynamic quantities for water and the simulation of the molecular dynamics of solution reactions and polypeptides.
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    Interactions of molecules with nucleic acids. VII. Evaluation and presentation of steric contours and molecules in bonding sites (1983)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 4 (1983), S. 366-378 
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    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: A technique to generate steric contours is developed and applied to the presentation of molecules that interact with DNA. The contours are generated by a Taylor's expansion in an extrapolation procedure designed to avoid infinite derivatives and correct for reversal in the direction of the drawing of the curve. A solution to the hidden line problem in computer graphics is presented for the case of steric contours ordered in parallel planes. The techniques developed in this article are demonstrated with stereographic orthographic projections for B-DNA, for intercalation complexes of lucanthone and actinomycin-D with DNA, and for the binding of benzo[a]pyrene diol epoxides (BPDEs) to guanine. The latter example illustrates the value of steric contours in demonstrating the lack of fit of BPDEs to B-DNA and by the need to unwind DNA to accommodate this molecule. Electrostatic contours in planes may be generated by this same procedure.
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    A theoretical study of the interaction of monomethylammonium with double-stranded oligonucleotides (1983)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 4 (1983), S. 390-398 
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    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: Theoretical computations are performed of the interaction specificities of the monomethylammoniumion with double-stranded oligonucleotides (dPu)n·(dPy)n in the B-DNA conformation. The effects of base sequence and chain length are examined. In short oligomers (n = 2, 3), the interaction energies of the cation are larger in the major groove of (dG)n·(dC)n than in the minor groove of (dA)n·(dT)n. As a consequence of further shaping of the grooves and building up of the phosphates, a marked reversal in the affinities of the cation for the grooves occurs at the (dPu)5·(dPy)5 and the p(dPu)5p·p(dPy)5p levels: it is the binding in the minor groove of the adenine-thymine oligomers that provides then the most favorable interaction energies.It is also shown, at the level of the double helices built from dinucleoside monophosphates, that the interaction of monomethylammonium in the minor groove occurs in specific configurations involving the three NH bonds of the cation, and two successive bases on one strand; this binding is sequence-specific, the order of inherent preferences being (TpA) 〉 (TpT) 〉 (ApA) 〉 (ApT).
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    A water-mediated tautomerism mechanism in formamide and amidine. An ab initio study (1983)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 4 (1983), S. 419-427 
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    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: Formamide, formamidic acid, and amidine water complexes were studied using 3-21G fully optimized structures and 6-31G energies. Hydrogen bonding and a water-mediated tautomerism mechanism were examined. The optimized complexes show that relaxation of the monomers has occurred. Hydrogen bond lengths and energies fall within the range of values found using other basis sets and other comparable systems.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540040318
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  • 95
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    Through-Space effects on vicinal proton spin-spin coupling constants mediated via hetero atoms: Nonequivalence of cis couplings in five-membered rings (1983)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 4 (1983), S. 438-448 
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    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: Theoretical studies are presented, aimed at the elucidation of through-space effects exerted by bridge-head oxygen and nitrogen atoms on cisoidal proton spin-spin coupling constants in 7-hetero-substituted norbornanes. The finite perturbation theory intermediate neglect of differential overlap (INDO) self-consistent field (SCF) molecular orbital (MO) method, modified according to the description given by Barfield [J. Am. Chem. Soc., 102, 1 (1980)], was employed. It is predicted that the known nonequivalence between Jendo-endo and Jexo-exo in norbornanes, which is in part mediated by the bridgehead methylene group (Barfield transmission effect), also occurs in 7-heteronorbornanes. A trend is recognized in which the nonequivalence induced by oxygen is rather smaller than that induced by the rear lobe of the N—H bond or by the nitrogen lone pair. It is shown that the Barfield effect also explains the observed nonequivalence between cisoidal H—Cβ—Cγ—H and H—Cγ—Cδ—H couplings in prolines. The calculations also predict similar, though smaller, effects on cisoidal couplings in the tetrahydrofuranyl ring system. Special attention was paid to the practical consequences of the existence of this effect with regard to the pseudorotation analysis of the five-membered sugar ring in nucleic acids. It is found that, in addition to the recently introduced correction for electronegativity and orientation of substituents [Haasnoot, de Leeuw, and Altona, Tetrahedron 36, 2783 (1980)], a cos2 dependency of 3Jcis upon the phase angle of pseudorotation must be taken into account, especially in the case of deoxyribofuranoses.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540040320
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  • 96
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    Calculations on the diphenylmethyl anion (1983)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 4 (1983), S. 470-481 
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    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: Semiempirical and ab initio calculations for the diphenylmethyl anion and related species are reported. MINDO/3 calculations indicate a coplanar anion with an enlarged bond angle of ∼139° to counteract the steric repulsions. MNDO calculations reveal an expanded bond angle with somewhat greater twist (21°). The ab initio calculations (STO-3G level) reveal an expanded central bond angle with an intermediate degree of phenyl twist. The results are compared with experimental data for this and related anions.
    Additional Material: 14 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540040404
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  • 97
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    A method for the calculation of normal-mode vibrational frequencies using symmetry coordinates. Application to the calculation of secondary deuterium isotope effects on carbocations (1983)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 4 (1983), S. 499-505 
    Details
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: A method is introduced for the calculation of normal-mode vibrational frequencies of polyatomic molecules based on numerical differencing of analytical gradients in symmetry coordinates. This procedure requires a number of gradient evaluations equal to the largest number of symmetry coordinates belonging to any single irreducible representation of the molecular point group (plus a single gradient evaluation at the equilibrium configuration), which is fewer than the 3N-6 (N atoms) gradient evaluations needed for schemes based on Cartesian or internal coordinates. While the proposed method will not generally be as efficient as procedures which involve the direct calculation of energy second derivatives analytically (as are now available for single-determinant wavefunctions) it appears to be equally accurate, and it should be the method of choice for frequency calculations involving multideterminant wavefunctions for which analytical second-derivative algorithms have yet to be developed. The method is illustrated by the calculation of equilibrium secondary deuterium-isotope effects on a number of reactions involving simple carbocations.
    Additional Material: 4 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540040408
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  • 98
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    Ab initio studies of structural features not easily amenable to experiment. 25. Conformational analysis of methyl propanoate and comparison with the methyl ester of glycine (1983)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 4 (1983), S. 494-498 
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    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: The molecular geometries of three conformations of methyl propanoate (MEP) (C—C—C=O torsions of 0°, 120°, and 180°) and the potential-energy surfaces of MEP (C—C—C=O torsions) and of the methyl ester of glycine (MEG) (N—C—C=O torsions) have been determined by ab initio gradient calculations at the 4-21G level. MEP has conformational energy minima at 0° and 120° of the C—C—C=O torsion, while the 60-90° range and 180° are energy maxima. For MEG there are two minima (at 0° and 180°) and one barrier to N—C—C=O rotation in the 60-90° range. The N—C—C=O barrier height is about twice as high (4 kcal/mol) as the C—C—C=O barrier. The 180° N—C—C=O minimum is characteristically wide and flat allowing for considerable flexibility of the N—C—C=O torsion in the 150-210° range. This flexibility could be of potential importance for polypeptide systems, since the N—C—C=O angles of helical forms are usually found in this region. The molecular structures of the methyl ester group CH3OC(=O)CHRR′ in several systems are compared and found to be rather constant when R = H and R′ = H, CH3, CH3CH2; or when R = NH2 and R′ = H, CH3, or CH(CH3)2.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540040407
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  • 99
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    Ground states of molecules. 64.For part 63, see ref. 1.MNDO Calculations for compounds containing bromine (1983)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 4 (1983), S. 542-551 
    Details
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: MNDO has been parametrized for bromine. Since d atomic orbitals (AOS) are not included, the calculations are restricted to BrI. Heats of formation, molecular geometries, ionization energies, and dioole moments are reproduced with useful accuracy.
    Additional Material: 5 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540040412
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  • 100
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    Counting of resonance structures for large benzenoid polynuclear hydrocarbons (1983)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 4 (1983), S. 556-562 
    Details
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: A method is presented for counting the number of resonance structures for large benzenoid polynuclear hydrocarbons. Structure counts for even systems are made and compared with those of the odd systems resulting from the removal of one of the π centers from various points in the even structure. A computer program for performing the calculations is also given.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540040414
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