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

The reactions of the CH(3)NH and (CH(3))(2)N 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 CH(3)NHNO and (CH(3))(2)NNO formation are similar, and it is concluded that primary amines form nitrosamines under the atmospheric conditions. CH(3)NHNO can, in contrast to (CH(3))(2)NNO, undergo isomerization via a barrier below the reactants entrance energy to CH(2)NHNOH, which through reaction with O(2) eventually leads to formation of CH(2)=NH on a short timescale. TDDFT, CASPT2 and MR-CI calculations show little difference between the n→π* transitions in CH(3)NHNO and (CH(3))(2)NNO and that the two molecules should have comparable photolysis lifetimes in the atmosphere.