Conformational Analysis f Organic Carbonyl Compounds. Part 3. A 1H AND 13C Nuclear Magnetic Resonance Study of Formyl and Acetyl Derivatives of Benzo[b]thiophene

The conformational analysis of formyl and acetyl derivatives of benzo[b]thiophen was carried out by employing nmr chemical shifts (1-H and 13-C) 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 C=O bond and the C=C bond having the higher double-bond character.