1H- and 13C-NMR studies on sulfinyl and sulfonyl derivatives of positional isomers of methyl thialaurate

Abstract

Sulfoxidation of the positional isomers of methyl thialaurate with m-chloroperoxybenzoic acid gave the corresponding sulfinyl and sulfonyl derivatives. In the 1H-NMR spectroscopic analysis, the sulfoxide function exerted a weaker deshielding effect than the sulfone group on the chemical shift of the protons of the adjacent methylene groups. The shift of the protons of the unperturbed α-methylene groups adjacent to the sulfone and sulfoxide function appeared at δ 2.97 and 2.67, respectively. It was possible to identify 7 of the 10 sulfinyl and sulphonyl derivatives by 1H-NMR spectroscopy. In the 13C-NMR spectroscopic analysis, the effect of the sulfinyl and sulfonyl function on the chemical shift of the adjacent α- and β-methylene carbons was quite similar, but significant enough to permit further differentiation of positional isomers. The chemical shifts of the α- and β-methylene carbons located adjacent to the sulfinyl function appeared at about 52.2 and 22.5 ppm, respectively. In the case of sulfonyl derivatives the shift of the α and β-methylene carbon atoms were found at about 52.4 and 21.6 ppm. It was possible to identify each positional isomer of the sulfinyl and sulfonyl derivatives of methyl thialaurate by this technique.