Theoretical Studies on Phenyl Group Rearrangement of Protonated Ketones

Gas-phase phenyl group migration within the protonated ketones has been studied MO theoretically using the AM1 method. The initial state structure shows relatively strong resonance delocalization of positive charge into the nonmigrating (Y) ring, while the ring migration (Z-ring) is nearly complete in the transition state. These results are reflected in the large (Y (>0) values and in the predominant contribution of resonance (r) over inductive (field, f) effect, r/f ranging from 1.3 () to 1.5 (). The cross-interaction constant is vanishingly small (=0.03) which is in contrast to the larger magnitudes for benzilic (=-0.48) and azibenzil (=-0.53) rearrangement processes. The relationship found between the extent of resonance contribution in the initial state and the magnitude of provides strong support for the proportionality between the magnitude of and the change in the intensity of interaction, , in the activation process.