Theoretical Study on Reaction Mechanism of Isocyanate Radical NCO With Ethene

摘要

The NCO + C2H4 reaction is simple and prototype for reaction of the NCO radical with unsaturated hydrocarbons, and it is considered to be important in fuel-rich combustion. In this article, we for the first time perform detailed theoretical investigations for its reaction mechanism based on Gaussian-3/ /B3LYP scheme covering various entrance and decomposition channels. The most favorable channel is firstly the NCO and C2H4 approach each other, forming a weakly-bound complex L1 OCN center dot center dot center dot C2H4, followed by the formation of isomer L2 OCNCH2CH2 via a small barrier of 1.3 kcal/mol. Transition states of any decomposable or isomeric channels for L2 in energy are much higher than reactants, which indicate that adduct L2 has stabilization effect in this NCO + C2H4 reaction. The direct H-abstraction channel leading to P1 HNCO + C2H3, might have an important contribution to the eventual products in high temperature. These results can well explain available kinetic experiment. Moreover, reaction mechanism for the title reaction is significantly different from the NCO + C2H2 reaction which proceeds on most favorably to generate the products HCN + HCCO and OCCHCN + H via a four-membered ring intermediate. (C) 2008 Wiley Periodicals, Inc. Int J Quantum Chem 109: 801-810, 2009