13C NMR substituent induced chemical shifts in the side-chain carbons of α,β-unsaturated sulphones

Abstract

The13C NMR chemical shifts of α,β-unsaturated sulphones of the types E-2-aryl-1-phenyl-sulphonylethylenes (series I) and E-1-arylsulphonyl-2-phenylethylenes (series II) have been measured in CDCl3 solution. The chemical shifts of the side-chain and a few ring carbons have been correlated with various single and multiparameter linear free energy relationships. Analysis of the13C NMR spectral data by a dual substituent parameter equation shows that the resonance effect is the dominant factor at C-α in series I and C-β in series II. The inductive effect is predominant at C-β in series I with a reverse substituent effect at this carbon atom. The reverse inductive contribution is explained in terms of π-polarisation mechanism.