Abstract
Two reaction mechanisms, inversion and rotation, are possible for intramolecular isomerization at C=N double bonds. Within the inversion mechanistic framework, there are two variants, one with planar TS and the other with perpendicular TS. We have previously demonstrated experimentally that the reaction of (CF3)2C=N-Ar proceeds via the inversion mechanism with gradual change from one variant to the other depending on the substituent on Ar. In the present study, MO/DFT and MD computations were carried out to analyze the modes of mechanistic change with substituent for the reactions of (CF3)2C=N-Ar and other related systems. It was found that the TS structure changes gradually from the planar to perpendicular geometry when the substituent on Ar becomes more electron withdrawing. Such change in the TS geometry arises from more effective conjugation between the lone pair on N and an electron-withdrawing substituent on Ar. The mechanism of the C=N isomerization will be fully discussed on the basis of the substituent effects on the barrier height and the TS geometry as well as the analyses of the intrinsic reaction coordinate and MD simulations.
