Theoretical study on the mechanism of C2Cl3 + NO2 reaction

Abstract

The radical-molecule reaction of C2Cl3 with NO2 is explored at the B3LYP/6-311G(d,p) and CCSD(T)/6-311+G(d,p) (single-point) levels. On the singlet potential energy surface (PES), the association between C2Cl3 and NO2 is found to be carbon-to-nitrogen attack forming the adduct C2Cl3NO2 (1) without any encounter barrier, followed by isomerization to C2Cl3ONO (2). Starting from 2, the most feasible pathway is the N–O1 bond cleavage which lead to P 1 (C2Cl3O + NO). Much less competitively, 2 transforms to the three-membered ring isomer c-OCCl2C–ClNO (4 a ) which can easily interconvert to c-OCCl2C–ClNO 4 b . Then 4 (4 a , 4 b ) takes direct C1–C2 and C2–O1 bonds cleavage to give P 2 (COCl2 + ClCNO). The lesser competitive channel is the 4 a isomerizes to the four-membered ring intermediate O-c-CNClOCCl2 (5) followed by dissociation to P3 (CO + ClNOCCl2). The concerted 1,2-Cl shift along with C1–O1 bond rupture of 4 b to form ONC(O)CCl3 (6) followed by dissociation to P 4 (ClNO + OCCCl2) is even much less feasible. Moreover, some of P 3 and P 4 can further dissociate to P 5 (ClNO + CO + CCl2). Compared with the singlet pathways, the triplet pathways may have less contribution to the title reaction. Our results are in marked difference from previous theoretical studies which showed that two initial adducts C2Cl3–NO2 and C2Cl3–ONO are obtained. Moreover, in the present paper we focus our main attentions on the cyclic isomers in view of only the chain-like isomers are considered by previous studies. The present study may be helpful for understanding the halogenated vinyl chemistry.