Mechanism of formation and monomolecular decomposition of aci-nitromethanes:: a quantum-chemical study

A quantum-chemical study of the reactions of formation of aci-nitromethane (aci-NM) and aci-dinitromethane (aci-DNM) and their decomposition with elimination of water was carried out. The methods employed were the ab initio RHF method with inclusion of electron correlation at the MP2 level of theory and the Dunning-Hay double zeta basis set augmented with polarization d-functions on heavy-element atoms, the DFT approach at the B3LYP level, and the semiempirical PM3 method. The formation of aci-NM and aci-DNM was found to be the limiting stage of the mechanism under study. For DNM, the barrier to reaction is substantially lower than for NM. The estimates of the heights of the barriers to formation found from density functional calculations at the B3LYP/6-311++G(dfp) level (258 U mol(-1) for aci-NM and 218.5 U mol(-1) for aci-DNM) are thought to be the most reliable.