Proton magnetic resonance study of magnetic non-equivalence. Substituent effect in some alkyl phenyl sulphoxides

Abstract

Non-equivalence of protons or methyl groups in para-substituted ethyl phenyl and isopropyl phenyl sulphoxides is investigated by proton magnetic resonance. It is found that para-substitution affects the chemical shift of non-equivalent protons in ethyl and non-equivalent methyl groups in isopropyl sulphoxides. One of the two non-equivalent methyl groups or methylene protons in isopropyl and ethyl sulphoxides respectively, is almost insensitive to para-substitution while the other is strongly influenced. This observation together with the spectral behaviour of these sulphoxides in a protonating solvent gives information on preferred conformations in these molecules.

The influence of distance between the sulphoxide group and the aliphatic protons has also been investigated. The magnetic non-equivalence was found to be still present at a point five bond-lengths from the centre of asymmetry.