Magnetic Nonequivalence in Higher Alkyl Groups

The phenomenon of magnetic nonequivalence has been growing in recent years. Unequal populations of the various conformers in such molecules are normally accepted as the cause of nonequivalence, but nuclei which are stereochemically nonequivalent are not necessarily magnetically nonequivalent. This nonequivalence has been demonstrated for molecules of the type ABDC⁸CHR₁R₂, where R + H, F, and Me. Although in principle the effect is quite general this has not been previously observed in "freely rotating" systems for groups larger than methyl. The role of steric factors, the size of the substituents and the distances between different parts of the molecules, have been discussed. In the present investigation these observations have been extended to demonstrate magnetic nonequivalence in higher groups including ethyl, isopropyl, propyl, isobutyl and benzyl by conversion of the appropriate alcohols to their mandelate esters.