Theoretical study on the mechanism of the CH2F + NO2 reaction

✍ Scribed by Jia-Xu Zhang; Ze-Sheng Li; Jing-Yao Liu; Chia-Chung Sun

• Publisher: John Wiley and Sons
• Year: 2006
• Tongue: English
• Weight: 561 KB
• Volume: 27
• Category: Article
• ISSN: 0192-8651
• DOI: 10.1002/jcc.20397

✦ Synopsis

Abstract

Despite the importance of the Fluoromethyl radicals in combustion chemistry, very little experimental information on their reactions toward stable molecules is available in the literature. Motivated by recent laboratory characterization about the reaction kinetics of Chloromethyl radicals with NO~2~, we carried out a detailed potential energy survey on the CH~2~F + NO~2~ reaction at the B3LYP/6‐311G(d,p) and MC‐QCISD (single‐point) levels as an attempt toward understanding the CH~2~F + NO~2~ reaction mechanism. It is shown that the CH~2~F radical can react with NO~2~ to barrierlessly generate adduct a (H~2~FCNO~2~), followed by isomerization to b~1~ (H~2~FCONO‐trans) which can easily interconvert to b~2~ (H~2~FCONO‐cis). Subsequently, Starting from b (b~1~, b~2~), the most feasible pathway is the CF and NO1 bonds cleavage along with NF bond formation of b (b~1~, b~2~) leading to P~1~ (CH~2~O + FNO), or the direct NO1 weak‐bond fission of b (b~1~, b~2~) to give P~2~ (CH~2~FO + NO), or the 1,3‐H‐shift associated with NO1 bond rupture of b~1~ to form P~3~ (CHFO + HNO), all of which may have comparable contribution to the reaction CH~2~F + NO~2~. Much less competitively, b~2~ either take the 1,4‐H‐shift and O1N bond cleavage to form product P~4~ (CHFO + HON) or undergo a concerted H‐shift to isomer c~2~ (HFCONOH), followed by dissociation to P~4~. Because the rate‐determining transition state (TSab~1~) in the most competitive channels is only 0.3 kcal/mol higher than the reactants in energy, the CH~2~F + NO~2~ reaction is expected to be rapid, and may thus be expected to significantly contribute to elimination of nitrogen dioxide pollutants. The similarities and discrepancies among the CH~2~X + NO~2~ (X = H, F, and Cl) reactions are discussed in terms of the electronegativity of halogen atom. The present article may assist in future experimental identification of the product distributions for the title reaction, and may be helpful for understanding the halogenated methyl chemistry. © 2006 Wiley Periodicals, Inc. J Comput Chem 27: 894–905, 2006