Theoretical investigation of the isomerization of N2O3 and the N-nitrosation of dimethylamine by asym-N2O3, sym-N2O3, and trans-cis N2O3 isomers

Eight isomers of N2O3, including five new conformers, were investigated at the CCSD(T)/6-311+G(d,p)//B3LYP/6-311+G(d,p) level. The computational results showed that asym-N2O3, sym-N2O3, and trans-cis N2O3 are stable isomers and asym-N2O3 is the most stable. The five new isomers are much more energetic than asym-N2O3 by 75-82 kcal/mol. All eight isomers are able to convert among each other through one-step or multi-step reactions. Additionally, the N-nitrosation of dimethylamine (DMA) by the three most stable N2O3 isomers, i.e., asym-N2O3, sym-N2O3, and trans-cis N2O3, was studied at the same theoretical level. Results indicated that the N-nitrosation of DMA by these three N2O3 isomers should easily occur, not only in the gas phase but also in water. Moreover, the energy barriers of these N-nitrosation reactions demonstrated that the values of sym-N2O3 and trans-cis N2O3 isomers are very close or even lower than that of asym-N2O3 isomer. Therefore, the results obtained in this work lead to the conclusion that along with the known asym-N2O3, being the nitrosating conformation for N2O3, the sym-N2O3 and trans-cis N2O3 isomers also have relatively strong nitrosating abilities. This conclusion is consistent with experimental results and will be helpful in better understanding the mechanism of N-nitrosation of amines by N2O3.