Intrinsic Barriers and Transition State Structures in the Gas Phase Carbon-to-Carbon Identity Proton Transfers from Nitromethane to Nitromethide Anion and from Protonated Nitromethane toaci-Nitromethane. Anab InitioStudy

Abstract

The identity carbon-to-carbon proton transfers between nitromethane and nitromethide anion and between oxygen protonated nitromethane and aci-nitromethane have been studied by ab initio methods. Group charges calculated by Mulliken and NPA methods as well as geometrical parameters such as pyramidal angles and CN bond lengths indicate that the transition states of these reactions are strongly imbalanced. Further evidence for the imbalance comes from a consideration of the relative energies of the various corners representing hypothetical intermediates on More O'Ferrall−Jencks diagrams. Our results for the CH3NO2/CH2NO2- system, in conjunction with previous findings on other CH3Y/CH2Y- systems, indicate an increase in the imbalance in the order CN ≪ CHO ≤ CHCH2 ≤ NO2 consistent with the notion that imbalances increase with π-acceptor strength of Y. However, when comparing the CH3N+O2H/CH2NO2H system with the CH3NO2/CH2NO2- system, the results are somewhat ambiguous as to whether the stronger π-acceptor (N+O...