Theoretical study of nitro–nitrite rearrangement of CH₃NO₂

Abstract

This paper is dedicated to Professor Sigerzi Hzizinc~gc~ otz the occasion of his 65th birthdayROBERTA P. SAXON and MEGUMU YOSHIMINE. Can. J . Chem. 70, 572 (1992). Calculations designed to characterize the transition state and determine the barrier height for rearrangement of nitromethane to methyl nitrite are reported. Structures of CH,NO,, C H 3 0 N 0 , dissociation products, CH3 + NOz and CH,O + NO, and the transition state for nitro-nitrite rearrangement have been optimized at the MCSCF/4-31G level. The geometry of the transition state may be approximately described as separated CH3 and NO, species with extremely long C-N and C 4 bond lengths, 3.396 and 3.654 A, respectively. Energies have been obtained by large-scale multireference single-and double-excitation CI calculations (6-3 lG:+ basis). The transition state is calculated to lie 56.7 kcal/mol above nitromethane (with zero-point energy). A C-N bond dissociation energy of 51.7 kcal/mol is obtained. Results are compared with the infrared multiphoton dissociation experiment of Wodtke, Hintsa, and Lee.

Experimental and Theoretical Studies of Roaming Dynamics in the Unimolecular Dissociation of CH3NO2to CH3O+NO

“…They confirmed a loose transition state (TS1 in Fig. 2), reported by Mckee [59] and Saxon et al [60] at a large C-N distance just below the C-N dissociation threshold and suggested it could be analogous to the roaming behavior seen in formaldehyde, i.e., roaming isomerization for the CH 3 NO 2 ↔ cis-CH 3 ONO reaction. They reproduced the experimental branching ratio of Ref.…”

Nitromethane−Methyl Nitrite Rearrangement: A Persistent Discrepancy between Theory and Experiment

“…The shape of the 10 active orbitals employed is similar to those displayed in Figure 1, which are the natural orbitals (NO) obtained from a CASSCF calculation. Note that, in previous studies, 18,19 only an active space of four-electron-in-four-orbital was used in MCSCF computations.…”

“…In other words, the latest results 20 substantiated the discrepancy not only between experimental and theoretical analyses but also between theoretical results reported in earlier papers. [13][14][15][16][17][18][19] Nevertheless, the nature of the TS for rearrangement, tight versus loose, has not been examined by an appropriate treatment.…”

Nitromethane dissociation: Implications for the CH3 + NO2 reaction

“…Unimolecular rearrangement of nitromethane to methyl nitrite, CH NO EF CH ONO 3 2 3 has been suggested [41] to be competitive with the simple bond fission (R1), but theoretical work [42,43] points to a high energy barrier for the isomerization pathway, making it negligible under conditions of interest. More important are secondary reactions of CH 3 NO 2 with the radical pool [27].…”