Nitrenes as intermediates in the thermal decomposition of aliphatic azides

Abstract

N 2 extrusion from hydrazoic acid, methyl azide, and ethyl azide to yield the corresponding nitrene has been studied with high-level ab initio calculations. Geometry optimizations of stationary points and surfaces crossing seams were carried out with the complete active space self-consistent field (CASSCF) method, and their energies were reevaluated with the second-order multireference perturbation (CASPT2) theory and corrected by the zero-point energy (ZPE). The analytic harmonic frequencies calculated at the CASSCF level have been used in the ZPE corrections. The decomposition reaction is a competitive mechanism between a spin-allowed and a spin-forbidden channel, giving the nitrene either in the singlet or triplet states. The energy barrier height for XN-N 2 bond fission is approximately the same in both channels for each azide, respectively. The spin-orbit (H SO ) interactions were determined at the minimum energy point on the seam of crossing between the singlet and triplet surfaces, the value ranges from 43.9 cm −1 in hydrazoic acid to 43.3 cm −1 in ethyl azide.

Understanding the rate of spin-forbidden thermolysis of HN3 and CH3N3

“…For the simplest azide, hydrazoic acid, the mechanistic picture emerging from experiment and theory is now fairly consistent, as discussed below. [10][11][12][13][14][15] For organic azides, including the simplest member of the series, CH 3 -N 3 , the picture is somewhat less clear. [16][17][18][19] In particular, there remains significant controversy regarding the role of open-shell triplet state intermediates following the extrusion of dinitrogen from the parent singlet species.…”

“…Other studies reached similar conclusions, 14 although it was also noted that the relatively small difference in barrier heights was consistent with the observation of both singlet and triplet products. 15 Early experiments on the pyrolysis of methyl azide in the gas phase showed that it was a unimolecular reaction, 21,27 which produces nitrogen, hydrogen, and HCN, 27,28 as well as methyleneimine CH 2 NH. 29 The activation energy was reported in 1933 by Leemarkers as about 43.5 kcal/ mol.…”

“…There have been several computational studies of the dissociation of methyl azide, 15,18,[34][35][36] including the MNDO study by Bock and Dammel mentioned above. 31 Nguyen et al studied the potential energy surfaces at the UMP2 / 6-31G͑d , p͒ level of theory and computed the rate constants for the decomposition of methyl azide.…”

Computational study for the second-stage cracking of the pyrolysis of ethylamine: Decomposition of methanimine, ethenamine, and ethanimine

“…A great deal of research has been carried out to assign the microwave, infrared, and electronic spectrum of this moiety [25][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40][41][42][43]. As a reactive species, MI can dissociate by 1,2-elimination of H 2 which has been studied both experimentally and theoretically [44][45][46][47][48][49][50][51][52][53][54][55]. Vinylamine and ethyleneimine are chemicals that widely used in industry; they were first detected as primary pyrolysis product of EA in the gas phase using microwave spectroscopic technique by Lovas et al [1,2].…”

The diradical (CH3)2CHN and its isomeric molecule (CH3)2C=HN: Generation and characterization

“…[1][2][3][4][5] The most thoroughly studied nitrenes are amidogen NH 6 and phenylnitrene C 6 H 5 N. 7 In contrast to aromatic nitrenes, much less is known about alkylnitrenes such as CH 3 -N, CH 3 CH 2 -N, ͑CH 3 ͒ 2 CH-N, and ͑CH 3 ͒ 3 C-N. Even basic physical and chemical data, such as ionization energies, are not available for nitrenes yet.…”