Reaction-Surface Topography for Hydride Transfer: Ab Initio MO Studies of Isoelectronic Systems CH₃O + CH₂O and CH₃NH₂ + CH₂NH₂⁺

The topography of the transition-state regions of the multidimensional potential energy surfaces for hydride transfer, (1) from methylamine to methaniminium and (2) from methoxide to formaldehyde, is described qualitatively on the basis of the characteristics (relative energies and curvatures) of critical points, each having negative curvature in the potential along the hydride-transfer reaction coordinate. Several new critical points on the HF/3-21G surfaces are reported. The geometry of hydride transfer depends upon steric effects, electrostatic interactions, and the possibility of 2e or 6e transition-state aromaticity. The varying interplay of these factors accounts for the differences between the reaction surfaces of the isoelectronic systems considered.