title: Self-association and stereochemistry study of 2-methylthio-, 2-dimethylaminocyclohexanone oximes and the parent cyclohexanone oxime.
abstract: X-ray diffraction analyses of 2-substituted cyclohexanone oximes C5H9(X)C=NOH [X = SMe (1), NMe2 (2)] and of the parent compound [X = H (3)] showed that their cyclohexyl rings are in a slightly distorted chair conformation. These compounds assume in the solid state the (E) configuration bearing the 2-substituents in the axial conformation. Compounds (1) and (2) exist as dimeric and polymeric hydrogen-bond associates, respectively. Low-temperature X-ray analysis of the cyclohexanone oxime (3) showed that the molecules are associated forming two independent trimers. The dimer in (1) and the trimer in (3) are built up via [O-H...N=C] hydrogen bonds, while the polymer of (2) is via the [OH...NMe2] hydrogen bond. The comparative IR nu(OH) and nu(C=N) analysis of the title compounds, in the solid state and in CCl4 solution, fully supports the nature of the associates for (1)-(3) obtained by X-ray diffraction. The IR azomethyne frequency shift analysis (Deltanu(C=N)) also suggests the occurrence of the pi(C=N)/sigma*(C-X) orbital interaction which stabilizes the axial conformations of (1) and (2).
authors.affiliation: Instituto de Química, Universidade de São Paulo, CP 26077, CEP, 05513-970 São Paulo, SP, Brazil. prolivat@quim.iq.usp.br
authors.forename: P R
authors.initials: PR
authors.lastname: Olivato
authors.forename: D S
authors.initials: DS
authors.lastname: Ribeiro
authors.forename: J
authors.initials: J
authors.lastname: Zukerman-Schpector
authors.forename: G
authors.initials: G
authors.lastname: Bombieri