Conformational analysis of organic carbonyl compounds. Part 3. A 1H and 13C nuclear magnetic resonance study of formyl and acetyl derivatives of benzo[b]thiophen

Abstract

The conformational analysis of formyl and acetyl derivatives of benzo[b]thiophen was carried out by employing n.m.r. chemical shifts (¹H and ¹³C) and coupling constants. By measuring the lanthanide-induced shifts (LIS) and simulating experimental chemical shifts the relative conformer stability was determined. The results show that all the molecules examined are present almost completely in the Z-conformation and that the stabilization of one conformer in this heterocyclic system seems due almost exclusively to the mesomeric interaction originating in the trans-arrangement of the CO bond and the CC bond having the higher double-bond character.