Theoretical studies on the mechanisms of NCCO + O2 reaction

The mechanisms of the reaction of NCCO with molecular oxygen are investigated at the G3MP2//B3LYP/6-311G(d,p) levels for the first time. The calculation results show that two mechanisms are involved, namely, O attack on α atom mechanism and O attack on β atom mechanism, with six products yielded. The most feasible channel is the addition of O₂ to β atom in NCCO radical leading to the energy-rich intermediate IM1, NCC(O)OO, which can isomerize to a four-center-structure IM3, and then undergoes C–C and O–C bond fission to form P1(NCO + CO₂) finally. The barriers are 27.3 and 25.4 kcal/mol, respectively. For other channels involved in the two mechanisms, with less stable initial adducts and higher barrier, they are less conceivable dynamically and thermochemically.