Integral Hellmann‐Feynman computations on H₃ABHn—H₂ABHn+1 rearrangements

Extensively optimized Lewis orbital (Frost model) structures are reported for CH 3 N, CH 3 NH + , CH 3 CH, CH 3 CH , CH 3 BH 2 , CH 2 NH, and CH 2 NH (spiro and planar). Electronic energy differences between these isoelectronic species were estimated by the integral Hellmann‐Feynman (i HF ) formula, with the hope that satisfaction of the Hellmann‐Feynman conditions would lead to accurate iHF values of energy changes. We observed a strongly nonlinear relation between the iHF error and the departure of the overlap of wave‐functions of the structures from unity. MO computations in common orbital (not determinantal) basis sets for CH 3 NH + CH 2 NH (planar), CH 3 NCH 2 NH, and CH 3 CHCH 2 CH 2 produced greatly improved i HF estimates of energy changes, reducing errors by as much as 80 times. Certain features of the static optimum structures and the transition densities suggested that the syn path for rearrangement of methyl carbene to ethylene is a general feature of rearrangements in these systems.