Free Energy Barrier to Rotation of the Amino Group in 2-Aminoacetophenone

The free energy of activation for hindered rotation of the amino group about the N-aryl bond in 2-aminoacetophenone is found to be 10.6 ± 0.5 kcal/mol in toluene solution at 233 ± 10 °K. Separate amino p.m.r. peaks are observed at low temperatures and these are strongly broadened by incompletely relaxed spin–spin coupling to the quadrupolar 14N nucleus, making a more accurate determination of activation parameters impractical. Some INDO molecular orbital calculations are performed in an attempt to rationalize the barrier magnitude.