Ab initio calculations relevant to the mechanism of chemical carcinogenesis by N-nitrosamines. Part 3.—Transition structures in nitrosamine formation and metabolism

A large number of fully optimised transition structures for rotation, inversion, N → O CH⁺₃ shifts, N → O CH₂OH⁺ shifts, N → O H⁺ shifts, N → O H₃O⁺ shifts, N → N H⁺ shifts and N → N H₃O⁺ shifts of first and second order are reported for several reactions of N-nitrosamines. The optimisations were carried out mainly at the restricted Hartree–Fock level (RHF) with a 4–21G split-valence basis set, but a representative H+-shift saddle point was studied with a 6–31G* double-zeta plus polarisation basis set at both the RHF and second-order Møller–Plesset levels. The relevance of these transition structures to the formation and decomposition of carcinogenic nitrosamines is discussed.