1,2,5-, 1,3,4- and 1,2,4-Oxadiazoles

Theoretical Chemistry Accounts - Tập 10 - Trang 435-446 - 1968
R. D. Brown1, B. A. W. Coller1, J. E. Kent1
1Department of Chemistry, Monash University, Clayton, Australia

Tóm tắt

Discrepancies found for some oxygen-containing compounds in a recent VESCF study of dipole moments have been further investigated by studying in detail furan, oxazole, isoxazole, and three isomeric oxadiazoles. In a preliminary geometrical study it was found that the method described previously for estimating ring angles and bond lengths satisfactorily accounted for observed geometries. However in those compounds where more than one ring atom carries lone pair σ-electrons, the electrostatic forces originating in these lone-pair dipoles have a considerable influence on ring geometry. When this is incorporated in the geometrical treatment, good agreement with known geometries is obtained. The effect of using Burns' rules for orbital exponents rather than Slater's rules to derive lone pair moments and the effect of including lone pair potentials in the hamiltonian have been studied. The best agreement between calculated and observed dipole moments (within 0.2 D) is obtained by using the BJ method that was used in the previous study but with revised values for some of the basic resonance integrals. The revised values are shown to be more in keeping with the relevant bond lengths and atomic numbers than the values previously used.

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Theoretical Chemistry Accounts

Tập 10

435-446

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