EFFETS DE SUBSTITUANTS EN SERIE DIALKYL-1,2 CYCLOHEXANIQUE-I. PERTURBATIONS CONFORMATIONNELLES INDUITES PAR LES INTERACTIONS STERIQUES ENTRE GROUPEMENTS VOISINS

Article abstract of DOI:10.1016/0040-4020(80)80115-3

The equilibration of the cis and trans isomers of four epimeric pairs of 3,4-dialkyl cyclohexanones (alkyl = Me,Et) have been studied quantitatively at different temperatures.The thermodynamic constants ΔH and ΔS exhibit considerable variations depending on the nature (Me or Et) of the substituents.These quantities were also calculated from statistical considerations.Theoretical and experimental values are in agreement.The origin of the observed variation an increase of the diaxial conformer proportion due to enhanced steric hindrance in other possible conformers when a methyl group is substituted by an ethyl group.This was confirmed experimentally by an NMR study of the trans-3,4-dialkyl cyclohexanone oximes.