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  • 1
    Electronic Resource
    Electronic Resource
    Structure of a ring enlarged product from the base induced rearrangement of dibromomethylenebenzonorbornene (1996)
    Springer
    Journal of chemical crystallography 26 (1996), S. 413-418 
    Details
    ISSN: 1572-8854
    Keywords: Cycloalkyne intermediates ; base-induced rearrangements ; ring expansion ; molecular mechanics ; Gaussian RHF/6-31G
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The base-catalyzed rearrangement reactions of 2-bromomethylenebenzonorbornene8 and 2,2-dibromomethylenebenzonorbornene9 were studied. Reaction of8 with potassiumtert-butoxide in THF gave only the enol ether11 whose formation is rationalized via a carbene-cycloalkyne mechanism. However, treatment of9 with phenyllithium in THF at −40°C gave the ringenlarged dibromide13 whose structure is reported herein. The ring-enlarged product13 is rationalized in terms of carbanionic rearrangement. Quantum mechanical calculations are consistent with these observations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01665821
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  • 2
    Electronic Resource
    Electronic Resource
    2,8,10,11-tetrachloro-12-oxahexacyclo-[7.2.1.02,8.03,7.04,11.06,10]dodeca-1,9-diol and disorder and mixed crystals in a system of tetracyclo-[6.3.0.04,11.05,9]undecanone and undecanol derivatives (1994)
    Springer
    Journal of chemical crystallography 24 (1994), S. 259-266 
    Details
    ISSN: 1572-8854
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract 2,8,10,11-Tetrachloro-12-oxahexacyclo[7,2.1.02.8.03.7.04.11.06.10]dodeca-1,9-diol is a strained cage molecule containing six five-membered rings and a four-membered ring. Twenty-five of the internal angles are less than 105° with 6 ranging from 89.5(3) to 97.4(3)°. The base promoted reaction of 3,6-dipyridyl-1,2,4,5-tetrazine with tetracyclo[6.3.0.04.11.05.9]undecane-3,6-dione yields the monoketone 6,7-[3′,6′-di(2″-pyridyl)-4′,5′-pyridizino]tetracyclo[6.3.0.04.11.05.9]-undecan-2-one. This compound crystallizes in the centrosymmetric space group P21/n with enantiomers related by a center of symmetry. In the crystal investigated the molecules are disordered with each site containing about 80% of one isomer and 20% of the enantiomer. When the ketone is hydrogenated and the product isolated, two different crystals were found to have a ratio of alcohol to ketone of .71/.29 and .75/.25 or about 3/1. The alcohol and ketone occupy the same sites, but with opposite stereochemistries.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01670354
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  • 3
    Electronic Resource
    Electronic Resource
    The structure of 11,12-bis[spiro(cyclopropyl)]-1,4,4a,5,8,8a,9a,10a-octahydro-1,4∶5,8-dimethano-9,10-anthraquinone (1995)
    Springer
    Journal of chemical crystallography 25 (1995), S. 63-68 
    Details
    ISSN: 1572-8854
    Keywords: Diels-Alder adduct ; molecular mechanics ; MOPAC ; bond asymmetry ; ring conformations ; absorption errors
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract In the solid state the 2∶1 Diels-Alder adduct between spiro[4.2]hepta-1,3-diene and p-benzoquinone has a planar cyclohexadione ring with a center of symmetry. Both planar and boat conformations have been observed in similar systems, and the relative stability of the two conformers is of interest. The adduct in the gas phase should contain a mirror plane perpendicular to the cyclohexadione ring; however, a data set collected on a crystal in a capillary resulted in a structure where some bond lengths related by this mirror plane differed by more than 4σ in the solid state. Molecular mechanics, MOPAC, and the Cambridge Structural Data Base were used to investigate the factors influencing the conformation of the cyclohexadione ring and the asymmetry across the noncrystallographic mirror plane. The energy differences between the planar and nonplanar ring system is small, and the conformation is determined by crystal packing. No reason for the bond length asymmetry could be found, and a recollection of data on a crystal exposed to the environment led to a structure with statistically equivalent bond lengths.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01667038
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  • 4
    Electronic Resource
    Electronic Resource
    Structure and properties of transition metal complexes of naphthoquinonedithiolate (1996)
    Springer
    Journal of chemical crystallography 26 (1996), S. 621-638 
    Details
    ISSN: 1572-8854
    Keywords: Quinonedithiolene complexes ; thiolates ; ferromagnetic interactions ; ab initio andsemi-empirical calculations
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Naphthoquinonedithiolate (nqdt) is a “noninnocent” ligand forming dithiolene transition metal complexes. Most [M(nqdt)2]−1 and [M(nqdt)2]−2 complex ions are planar with each forming an isomorphous series with the (n-butyl)4N+ (tba) counter ion. The cobalt complex is isolated as a step dimer (tba)2[Co(nqdt)2]2 where two square-planar monomer units are bonded via Co−S intermolecular interactions.Ab initio andsemi-empirical calculations are used to investigate the complex ions. The complexes form tba single crystals only with difficulty, and an extensive study with ions of various shapes and charges failed to identify a more satisfactory counter ion. The magnetic susceptibilities of four complexes are discussed. The (tba)[Ni(nqdt)2] complex undergoes a weak ferromagnetic transition at 4.43 K while a mixed oxidation state Mn(II) complex exhibits a weak ferromagnetic transition at 40K. The crystal structures of (tba) [Cu(nqdt)2], (tba)[Ni(nqdt)2], (tba)2[Ni(nqdt)2], (tba)2[Pd(nqdt)2], {(tba)[Co(nqdt)2]}2 and four side reaction products 5,7,12,14-tetrahydrodibenzo-[b,i]thianthrene-5,7,12,14-tetraone (2), benzocyclohexa-2,5-diene-1,4-dione-1,3-thiole-2-thione (3), a thiomethyl derivative (4), and an unusual oxidatively coupled product (5) are reported.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01668623
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  • 5
    Electronic Resource
    Electronic Resource
    Nepetanudone, a dimer of the α-pyrone 5,9-dehydronepetalactone (1998)
    Springer
    Journal of chemical crystallography 28 (1998), S. 517-519 
    Details
    ISSN: 1572-8854
    Keywords: α-Pyrone dimer ; genus Nepeta ; [4+4] cycloaddition
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The title compound C20H24O4 crystallizes in the orthorhombic space group P21212, with a = 10.245(3), b = 17.103(3), c = 9.879(3) Å, D c = 1.260 g cm −3, and Z = 4. Nepetanudone is postulated to be formed by a [4+4] cycloaddition of two 5,9-dehydronepetalactone moieties to give an asymmetric dimer in which each pair of atoms is magnetically nonequivalent. The compound was recovered from extracts of Nepeta nuda ssp. albiflora.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1023287804704
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  • 6
    Electronic Resource
    Electronic Resource
    The structure of 7,14-dicarbonylethoxyacenaphth[l,2-k]-fluoranthene and its tetracyanoquinodimethane charge transfer complex (1993)
    Springer
    Structural chemistry 4 (1993), S. 53-57 
    Details
    ISSN: 1572-9001
    Keywords: Molecular mechanics simulation ; crystal structure analysis ; charge transfer
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract A molecular mechanics simulation of the structure of 7,14-dicarbonylethoxyacenaphth[l,2-k]fluoranthene,1, indicated a preferred geometry for the hindered substituents in which the carbonyl groups were constrained to an anti conformation because of the steric hindrance associated with the in-plane buttressing hydrogen atoms. X-ray crystallographic analysis of1 verifies the correctness of the computation. Compound1 and tetracyanoquinodimethane,2, form a charge transfer complex, and a crystal structure analysis shows a slightly offset, nearly parallel arrangement of the acceptor with the π cloud of the donor. The interplanar distance of 3.45 Å between acceptor and donor lies within the statistical limits of the interplanar distance of π complexes formed between2 and a variety of PAH donors. The steric hindrance caused by the substituents in1 appears to offer only minimal interference to the formation of the π complex.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00672099
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  • 7
    Electronic Resource
    Electronic Resource
    Rearrangement of a trishomocubane derivative to a tetracyclo[6.3.0.02,6.03,10]undec-4-ene (1996)
    Springer
    Structural chemistry 7 (1996), S. 73-77 
    Details
    ISSN: 1572-9001
    Keywords: Tetracycloundecane ; d 3-trishomocubane ; tetracycloundec-4-ene ; molecular mechanics ; semiempirical calculations ; X-ray analysis ; carbonium ion rearrangements
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Reaction of 8,8,11,11-tetrafluoropentacyclo[5.4.0.02,6.03,10.05,9]undecane with idio trimethylsilane leads to the expectedd 3-trishomocubane derivative, but reaction with the more electrophilic boron tribromide yields a tetracyclo[6.3.0.02,6.03,10]undec-4-ene derivative which was characterized by X-ray diffraction. The most easily visualized pathway for this transformation would be an initial rearrangement of the starting material to ad 3-trishomocubane followed by additional bond breaking to form the undec-4-ene compound. Molecular mechanics calculations indicate the brominatedd 3-trishomocubane is about 4 kcal/mol more stable than the brominated undec-4-ene molecule and the associated carbonium ions show the same ordering. These data would indicate an alternate reaction pathway must be operative; however, semiempirical calculations predict the reverse ordering of the above energies.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02275451
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  • 8
    Electronic Resource
    Electronic Resource
    Structures of three substituted pentacyclo[5.4.0.02, 6.03, 10.05, 9]undecanes and a computational analysis of bond lengths (1994)
    Springer
    Structural chemistry 5 (1994), S. 21-35 
    Details
    ISSN: 1572-9001
    Keywords: Cage compounds ; long C-C bonds ; X-ray diffraction ; molecular mechanics ; semi-empirical calculations ; ab initio calculations
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract 5-Methyl-2-phenylpentacyclo[5.4.0.02, 6.03, 10.05, 9]undecane-8, 11-dione,5-methyl-2-phenylpentacyclo [5.4.0.02,6.03,10.05,9]undecane-8-one-11-ol,and 5-methyl-2-phenylpentacyclo[5.4.0.02,6.03,10.05,9]undecane-8,11-diol are three cage compounds which differ only in the oxidation state at C(8) and C(11). The three compounds contain a four-membered, a six-membered, and four five-membered rings fused into a cagelike structure. An X-ray structure analysis shows the C(1)-C(7) and C(9)-C(10) bonds in the diketo cage to be 1.606(2) and 1.586(2) Å, which are significantly longer than in the other two molecules. In order to assess the effects of strain, steric, and electronic factors in these compounds, we investigated the unsubstituted parent cage compounds and a series of derivatives by molecular mechanics (MM3), AMPAC (AM1), MOPAC (PM3), and GAUSSIAN 90 calculations. These data suggest that dipolar through space interactions are responsible for the bond elongation and not aπ −→σ * interaction, which has been postulated in parallelπ-systems originating from a common bond. A small degree ofπ −→σ * “through-bond” interaction may contribute to the lengthening in the dimethylene cage analogues.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02278692
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  • 9
    Electronic Resource
    Electronic Resource
    Structure of a C26H28 alkene formed via titanium-promoted reductive dimerization of 4-(spirocyclopropyl)-pentacyclo[5.4.0.02,6.03,10.05,9]undecan-8-one (1994)
    Springer
    Structural chemistry 5 (1994), S. 367-373 
    Details
    ISSN: 1572-9001
    Keywords: Cage compounds ; C26H28 alkene ; reductive dimerization ; X-ray diffraction ; molecular mechanics ; semiempirical calculations ; ab initio calculations
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract A spiro-fused C26H28 “cage≓ dimer hydrocarbon contains two three-membered rings, two four-membered rings, eight five-membered rings, and two six-membered rings. The molecule is calculated by molecular mechanics to have 902 kJ/mol of strain energy distributed primarily between angle strain (457 kJ/mol) and torsional interactions (368 kJ/mol). Molecular mechanics calculations and a geometry-optimized ab initio calculation are used to analyze the bond lengths and bond angles in the molecule. There is one major discrepancy between observed and calculated distances.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02252895
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