G. De Petris

Gas phase protonation of alkyl and phenyl azides

Abstract Gas-phase protonation of azides has been investigated with mass spectrometric and computational techniques. The proton affinities of MeN3, EtN3 and PhN3, derived from bracketing experiments, are respectively 199±3, 210±5, and 196±3 kcal mol−1. The structures and the energetics of MeN3 and MeN3H+ have been investigated by ab initio MO techniques, a proton affinity of MeN3 of 195.3 kcal mol−1 at the 6-31G **//6-31G* level of theory being obtained, in agreement with the experimental value. The loss of N2 from MeN3H+, yielding the MeNH+ nitrenium ion, has also been theoretically estimated (by ab initio techniques) to be endothermic by ca. 15 kcal mol−1, again in accord with experimental observations. In fact, MeN3H+ is fairly stable, being the base peak in the CH4 chemical ionization spectrum of MeN3, while PhN3H+ is but a minor peak in the CH4 chemical ionization spectrum of PhN3, undergoing extensive N2 loss. Collisional Activation (CA) mass spectrometry of the charged fragment formed upon N2 loss from CH3N3H+ suggests rearrangement to CH2=NH+2, while the PhNH+ fragment retains the nitrenium-ion structure, reacting with benzene to give a C12H12N+ derivative whose CA spectrum is closely similar to that of protonated diphenylamine.

Concerning the Lewis acidity of NO+ and NO2+ as measured by their affinity to selected bases

Recently published theoretical results concerning the NO+ and NO2+ gas-phase affinities of a few selected molecules, as well as the correlation between the above quantities and the corresponding proton affinities, are examined in the context of the much larger body of experimental and theoretical data already reported in the literature.