Rotational isomerism in 2,4,6-tri-tert-butylanilides

Z-Rotamers of several 2,4,6-tri-tert-butylanilides slowly isomerize at rt in CDCl3 to E-rotamers, yielding equilibrium mixtures of Z- and E-rotamers after standing for 1 week. The equilibrium ratios between the anilide rotamers in the solution depend strongly on the bulkiness of the acyl substituents as well as the formation of intramolecular hydrogen bond. Heating equilibrium mixtures in the solid state produced complete isomerization to the Z-rotamer.