NMR and molecular mechanics studies on configurational isomerism and conformational equilibrium of chiral cyclohexenones

Chiral diastereomers of 2-isopropyl-5-methyl-6-(4-phenyl)benzylcyclohex-2-e none and their isomer 2-(4-phenylbenzyl)-3-methyl-6-isopropylcyclohexanone, which are products of an acid-catalyzed intramolecular rearrangement of 3R ,6R-2-(4-phenylbenzylidene)-3-methyl-6-isopropylcyclohexamoe, were investig ated to show that conformational analysis by molecular mechanics and H-1 NM R spectroscopy permits an integrated solution of three structural problems: double bond location in an aliphatic ring for isomeric products; determina tion of the stereochemical configuration for the two diastereomers; evaluat ion of the conformational equilibrium between the diastereomers. Based on t he results of calculations, this is achieved by estimating the configuratio n- and conformation-sensitive proton spin-spin coupling constants of the cy clohexenone ring for alternative structures and correlating them with H-1 N MR data.