Theoretical study on reaction mechanism of the fluoromethylene radical with nitrogen dioxide

The complex doublet potential energy surface for the reaction of 1CHF with NO2, including 14 minimum isomers and 30 transition states, is explored theoretically at the B3LYP/6-311G(d,p) and CCSD(T)/6-311G(d,p) (single-point) levels of theory. The initial association between 1CHF and NO2 is found to be the carbon-to-middle-nitrogen attack forming an energy-rich adduct a (HFCNO2) with no barrier, followed by concerted O-shift and C--N bond rupture leading to product P2 (NO + HFCO), which is the most abundant. In addition, a can take a 1,3-H-shift to isomer b (FCN(O)OH) followed by the dissociation to form the second feasible product P4 (OH + FCNO). The least favorable pathway is that b undergoes a concerted OH-shift to form d (HO(F)CNO), which will dissociate to product P5 (HF+OCNO) via side HF-elimination. The secondary dissociation of P5 may form product P7 (HF+NO+CO) easily. Furthermore, the 1CHF attack at the end-O of NO2 is a barrier-consumed process, and thus may only be of significance at high temperatures. The comparison with the analogous reactions 1CHCl + NO2 is discussed. The present study may be helpful for probing the mechanism of the title reaction and understanding the halogenated carbine chemistry.