Theoretical investigation of the isomerization of N 2O 3 and the N-nitrosation of dimethylamine by asym-N 2O 3, sym-N 2O 3, and trans– cis N 2O 3 isomers

Abstract

Eight isomers of N 2O 3, 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-N 2O 3, sym-N 2O 3, and trans– cis N 2O 3 are stable isomers and asym-N 2O 3 is the most stable. The five new isomers are much more energetic than asym-N 2O 3 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 N 2O 3 isomers, i.e., asym-N 2O 3, sym-N 2O 3, and trans– cis N 2O 3, was studied at the same theoretical level. Results indicated that the N-nitrosation of DMA by these three N 2O 3 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-N 2O 3 and trans– cis N 2O 3 isomers are very close or even lower than that of asym-N 2O 3 isomer. Therefore, the results obtained in this work lead to the conclusion that along with the known asym-N 2O 3, being the nitrosating conformation for N 2O 3, the sym-N 2O 3 and trans– cis N 2O 3 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 N 2O 3.