Conformational analysis. Part 10. A theoretical and nuclear magnetic resonance (lanthanide-induced shift) study of the conformation of cyclohex-2-enone

Abstract

A combined study of the conformational behaviour of cyclohex-2-enone has been carried out using theoretical methods (MNDO, MMPI,STO-3G) and the lanthanide-induced shift (l.i.s.) n.m.r. technique. The theoretical results are all consistent with a predominant envelope conformation (pucker angle 22–26°), the most stable half-chair conformer (torsion angle ca. 15°) is ca. 0.5–1.5 kcal mol^–1 less stable. The results of l.i.s. analysis give excellent agreement with both the half-chair and envelope conformations. In this not very well determined system this technique cannot differentiate between these very similar conformers.