Do primary nitrosamines form and exist in the gas phase? A computational study of CH3NHNO and (CH3)2NNO

Abstract

The reactions of the CH₃NH and (CH₃)₂N radicals with NO have been studied using quantum chemistry methods to compare the formation and stability of primary and secondary nitrosamines. The calculations show that the entrance part of potential energy surfaces of CH₃NHNO and (CH₃)₂NNO formation are similar, and it is concluded that primary amines form nitrosamines under the atmospheric conditions. CH₃NHNO can, in contrast to (CH₃)₂NNO, undergo isomerization via a barrier below the reactants entrance energy to CH₂NHNOH, which through reaction with O₂ eventually leads to formation of CH₂NH on a short timescale. TDDFT, CASPT2 and MR-CI calculations show little difference between the n → π* transitions in CH₃NHNO and (CH₃)₂NNO and that the two molecules should have comparable photolysis lifetimes in the atmosphere.