Ion-molecule reactions between ionized nitrile oxides and neutral nitrite
Résumé
The ion-molecule reactions of ionized nitrite oxide, R-C=N+-O-., with several neutral nitrites have been studied using both tandem mass spectrometric techniques and ab initio molecular orbital calculations. Ionized oxygen atom transfer as well as a formal substitution of nitric oxide by the neutral reagent in the radical cation were the main processes. Whereas the former reaction yields the corresponding ionized nitrite oxide, the second process gives an even electron species tentatively ascribed, following high-kinetic energy collisional activation experiments, to an aromatic azirinyl cation. All the experimental data point to a two-step reaction sequence where the primarily formed intermediate ions competitively dissociate by the loss of nitrite or of nitric oxide respectively giving nitrite oxide ions and azirinyl ions. From a theoretical point of view, the mechanism of the simplest reaction HCNO.+ + HCN --> cyclo-HCCHN+ + NO. has been explored at the MP2/6-31G(d) level of theory. The most favorable reaction profile involves the formation of a C-N bond between the positively charged carbon atom of HCNO.+ and the nitrogen atom of cyanhydric acid giving an HCNO.+/HCN intermediate which isomerizes into an ionized nitrosoazirine before losing NO..