An Evaluation of Solvent Effects on lsomerization Mechanisms in Diimide and Methylenimine

Inversional and rotational isomerization mecha'!lisms in N2H2 and CH2NH have been studied by an ab initio procedure including in the solute hamiltonian the reaction potential of a solvent mo. delled as a dielectric continuum. The basic computed quantity is a solution free energy parametrically dependent on the solute internal coordinates. The solvent effect, mainly related to the hybridization state of the nitrogens and to the relative orientation of their lone pairs, in N2H2 leads to a lowering of both barriers, and to a stabilization of the cis form with respect to trans. In CH2NH, the inversional baorrier is increased, whereas the rotational one remains unchanged.