Reaction Mechanisms of C₂Cl₃ + NO₂ via Nitro and Nitrite Adducts

Abstract

The atmospherically and environmentally important reaction of chlorinated vinyl radical with nitrogen dioxide (C 2 Cl 3 + NO 2 ) is investigated by step-scan time-resolved Fourier transform infrared emission spectroscopy and electronic structure calculations. Vibrationally excited products of CO, NO, Cl 2 CO, and NO 2 are observed in the IR emission spectra. Geometries of the major intermediates and transition states along the potential energy surface are optimized at the B3LYP/6-311G(d) level, and their energies are refined at the CCSD(T)/ 6-311+G(d) level. The reaction mechanisms are characterized to be barrierless addition-elimination via nitro (C 2 Cl 3 -NO 2 ) and nitrite (C 2 Cl 3 -ONO) adducts. Four energetically accessible reaction routes are revealed, i.e., the decomposition of the nitrite adduct forming C 2 Cl 3 O + NO and its sequential dissociation to CO + NO + CCl 3 , the elimination of ClNO from the nitrite adduct leading to ClNO + Cl 2 CCO, the Cl-atom shift of the nitrite adduct followed by the decomposition to CCl 3 CO + NO, and the O-atom shift of the nitro adduct followed by C-C bond cleavage forming ClCNO + Cl 2 CO. In competition with these reactive fluxes, the back-decomposition of nitro or nitrite adducts leads to the prompt formation of vibrationally excited NO 2 and the long-lived reaction adducts facilitate the vibrational energy transfer. Moreover, the product channels and mechanisms of the C 2 Cl 3 + NO 2 reaction are compared with the C 2 H 3 + NO 2 reaction to explore the effect of chlorine substitution. It is found that the two reactions mainly differ in the initial addition preferentially by the N-attack forming nitro adducts (only N-attack is plausible for the C 2 H 3 + NO 2 reaction) or the O-attack forming nitrite adducts (O-attack is slightly more favorable and N-attack is also plausible for the C 2 Cl 3 + NO 2 reaction). The addition selectivity can be fundamentally correlated to the variation of the charge density of the end carbon atom of the double bond induced by chlorine substitution due to the electron-withdrawing effect of chlorine groups.

Competitive reaction pathways of C2Cl3+ NO via four-membered ring and bicyclic ring intermediates

“…According to its spectral position, the intense emission band from 1740 to 1920 cm À1 (band I) are most likely ascribed to the C-O stretching mode of Cl 2 CO (fundamental frequency at 1827 cm À1 ), which are predicted to be the major products theoretically. This IR emission band due to Cl 2 CO has also been observed in the reaction of C 2 Cl 3 with O 2 9 and NO 2 11 in our previous studies. The assignment of this band to another possible species with fundamental frequency at 1884 cm À1 , ClCO, 34 can be ruled out.…”

“…3(c), these two bands are rotationally irresolvable at the spectral resolution of 0.5 cm À1 , suggesting that they are not originated from diatomic products of NO and CO although their IR bands also fall within these spectral ranges, because rotationally resolved structure should be well resolved for NO and CO at 0.5 cm À1 . 11 Instead, these unresolved bands should be ascribed to polyatomic molecules. The assignment of these structureless bands is made possible with the aid of our theoretical calculations which have predicted the feasible reaction products.…”

“…7 As a serial work prior to this study, we have studied the reaction products and mechanisms of C 2 Cl 3 radical with O 2 and NO 2 theoretically and experimentally. [8][9][10][11] Although there has been a lack of investigation concerning the title reaction C 2 Cl 3 + NO, sufficient information can be retrieved from the literature for its counterpart reaction C 2 H 3 + NO which may provide valuable hints for the current work. [12][13][14][15][16][17][18] In early experiments performed in the context of the mercury-photosensitized decomposition of acetylene/NO mixtures 13 and H or Cl initiated reactions of acetylene with NO, 12 Sherwood and Gunning observed that HCN and H 2 CO are the dominant products of the C 2 H 3 + NO reaction at room temperature and suggested that the reaction proceeds through an OCCN four-membered ring intermediate (1,2-oxazete) followed by N-O and C-C bond breaking.…”

Combustion and Pyrolysis Kinetics of Chloropicrin

“…CH3NO2 33 , CHCl2NO2 34 and C2Cl3NO2 35 . The authors showed that NO2 and the carbon radicals (CH3, CHCl2 or C2Cl3) react by combination to form either the reactant (addition of the N side of NO2) or a R-ONO species (addition of the O side of NO2).…”

“…The kinetic constant of the first reaction was estimated from the correlations involved in the EXGAS software and that of the second one by analogy with the reaction CCl 3 + Cl, which produces a C–Cl bond with a close BDE. Decomposition reactions of the produced radicals were included, based on analogueies with species featuring similar chemical structures, like CH 3 NO 2 , CHCl 2 NO 2 , and C 2 Cl 3 NO 2 . The authors showed that NO 2 and the carbon radicals (CH 3 , CHCl 2 , or C 2 Cl 3 ) react by combination to form either the reactant (addition of the N side of NO 2 ) or a RONO species (addition of the O side of NO 2 ).…”