Proton magnetic resonance studies of cyclic compounds. Part VII. The effect of axial alkyl groups in causing a flattening of the cyclohexane ring in cis-1-alkyl-4-phthalimidocyclohexanes

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Abstract
Values of the vicinal proton–proton coupling constants J3e4a in cis-(but not trans) 1-alkyl-4-phthalimidocyclohexanes increase with increasing size of the alkyl substituent, providing evidence that flattening of the cyclohexane ring is induced by bulky axial substituents. A value of 3·8–3·9 kcal/mole is determined indirectly for the conformational free energy (–ΔG) of the phthalimido group.