Carbon‐13 NMR spectra of monosulphones and disulphones: Substitution rules and conformational effects

Publisher Website
Google Scholar
Abstract
Carbon‐13 NMR spectra have been obtained for 27 aliphatic monosulphones and 13 aliphatic disulphones. Substitution rules have been formulated which allow the prediction of chemical shifts when a CH2 group in a hydrocarbon is replaced by an SO2 group, or when an H atom in a sulphone is replaced by an alkyl group. Carbon atoms β to a sulphone group show a marked upfield shift effect which is sensitive to the conformation about the CS bond; atoms in the trans position experience an upfield shift (−9.39±1.64 ppm) compared with those in the gauche position. An assignment of the meso (m) and racemic (r) β‐carbon peaks in di‐sec‐butyl sulphone was made by synthesis of the optically active compound. |δm–δLr| decreases with increasing temperature for both β–carbon atoms; this effect was interpreted in terms of two available conformers for each of the m and r compounds, those for the m form having the same energy and entropy, and those for the r form having ΔS=0.6 J K−1 mol−1 and ΔH=0.8 kJ mol−1. Observed chemical shifts for the disulphones were compared with those estimated by the application of the first set of substitution rules.