Multinuclear NMR spectroscopy and semi-empirical MNDO-PM3 quantum chemical investigations of the compounds C 6H 5XY (X=S, SO, SO 2; Y=CF 3, CH 3)

Abstract

The compounds C 6H 5XCF 3 and C 6HXCH 3 (X=S, SO, SO 2) have been investigated by multinuclear 1H, 13C, 17O, 19F and 33S NMR spectroscopy and quantum chemical methods (MNDO in the PM3 parametrization). Compounds with XCF 3, SOCH 3 and SO 2CH 3 groups have been characterized with effective non-planar conformations. A nearly planar effective conformation has been found for C 6H 5SCH 3. As the two lone pairs (LP) of sulphur in the sulphides are essentially non-equivalent with their orbital energies differing considerably, only one LP (with a higher energy level) can participate in the p-π conjugation. In compounds with XCF 3, SOCH 3 and SO 2CH 3 groups, the electron-withdrawing π-inductive effect is the main factor determining the π-charge distribution in the benzene ring. The p-π conjugation is essentially distorted in C 6H 5SCF 3 due to its various conformations. Electron-donating p-π conjugation only contributes considerably to the π-charge distribution in the benzene ring in C 6H 5SCH 3. An interpretation of the NMR spectra of the considered compounds is given on the basis of the quantum chemical calculations.