Theoretical study on the mechanism of the ³CH₂ + NO₂ reaction

Abstract

The complex doublet potential energy surface of the CH(2)NO(2) system is investigated at the B3LYP/6-31G(d,p) and QCISD(T)/6-311G(d,p) (single-point) levels to explore the possible reaction mechanism of the triplet CH(2) radical with NO(2). Forty minimum isomers and 92 transition states are located. For the most relevant reaction pathways, the high-level QCISD(T)/6-311 + G(2df,2p) calculations are performed at the B3LYP/6-31G(d,p) geometries to accurately determine the energetics. It is found that the top attack of the (3)CH(2) radical at the N-atom of NO(2) first forms the branched open-chain H(2)CNO(2) a with no barrier followed by ring closure to give the three-membered ring isomer cC(H(2))ON-O b that will almost barrierlessly dissociate to product P(1) H(2)CO + NO. The lesser followed competitive channel is the 1,3-H-shift of a to isomer HCN(O)OH c, which will take subsequent cis-trans conversion and dissociation to P(2) OH + HCNO. The direct O-extrusion of a to product P(3) (3)O + H(2)CNO is even much less feasible. Because the intermediates and transition states involved in the above three channels are all lower than the reactants in energy, the title reaction is expected to be rapid, as is consistent with the measured large rate constant at room temperature. Formation of the other very low-lying dissociation products such as NH(2) + CO(2), OH + HNCO and H(2)O + NCO seems unlikely due to kinetic hindrance. Moreover, the (3)CH(2) attack at the end-O of NO(2) is a barrier-consumed process, and thus may only be of significance at very high temperatures. The reaction of the singlet CH(2) with NO(2) is also briefly discussed. Our calculated results may assist in future laboratory identification of the products of the title reaction.

An experimental and kinetic modeling study of premixed nitromethane flames at low pressure

“…The current rate constant is based on the estimate for atmospheric pressure by Tricot et al [26]. The activation energy is consistent with the recent estimate for the barrier by Liu et al [25]. Even with the low A-factor assumed in the present study, this step remains the main consumption channel for CH 2 NO 2 .…”

“…The reaction occurs by ring closure to yield a three-membered ring isomer that will almost barrierlessly dissociate to products [25]. The current rate constant is based on the estimate for atmospheric pressure by Tricot et al [26].…”

Theoretical study on the mechanism of the 1CHCl + NO2 reactions

“…It is very useful to compare the mechanism of the title 1 CHCl + NO 2 reaction with that of the analogous reaction 3 CH 2 + NO 2 . Recently, Feng et al18 have studied the doublet PES of the 3 CH 2 + NO 2 reaction in detail and obtained the mechanism which may be concluded as: …”

A matrix isolation study of the Cs symmetric OCNO(X 2A″) radical

“…The temporal evolution of the column density of the nitroformyl radical looks to follow pseudo-first order kinetics for all isotopomers. The plots were therefore fit according to eqn (2). Here, a is the pre-exponential factor and k is the rate constant for the formation of the nitroformyl radical.…”

“…The bent OCNO radical (C s , X 2 A 00 ) presents an important intermediate in combustion flames as well as atmospheric and astronomical environments. [1][2][3] However, a literature search yields only sparse accounts of this molecule. Electronic structure calculations suggest that two resonance structures of this molecule exist (Fig.…”