Theoretical Study on the Mechanism of the 1CHF+N2O Reaction

Abstract

The complex singlet potential energy surface of the CHFN2O system is investigated at the QCISD(T)/ 6-311G(d,p)//B3LYP/6-31G(d,p) level in order to explore the possible reaction mechanism of 1CHF radical with N2O. Twenty-eight minimum isomers and sixty-four transition states are located. For the most relevant reaction pathways, the high-level QCISD(T)/6-311G(2df,p) single-point calculations are performed at the MP2/6-311G(d,p) geometries to accurately determine the energetics. In various possible initial association ways, the end-N attack leading to HFCN2O a1 is the most feasible pathway with the barrier of 13.5 kcal/mol, whereas for the other attack ways, each involves a higher barrier and thus may not be of significance even at very high temperatures. Starting from HFCN2O a, the most favorable reaction pathway is the almost barrierless dissociation of trans-HFCN2O a leading to product P1 HFCN+NO via the direct N−N bond cleavage. A comparable pathway is the ring-closure of cis-HFCN2O a3 leading to four-membered ring isomer b followed by the direct dissociation to P4 N2+HFCO. The less and least competitive pathways are the concerted F-shift and N−N bond rupture to P2 HCN+FNO as well as the concerted H-shift and N−N bond cleavage to P3 FCN+HNO, respectively. However, these primary products P1, P2, P3, and P4 cannot further dissociate due to thermodynamical and kinetic factors. By comparison, it is found that the B3LYP-calculated and MP2-calculated results are generally in agreement. In addition, the discrepancies and similarity between the title reaction and analogous 1CH2+N2O reaction are discussed. The present paper may assist in future experimental identification of the product distributions for the title reaction and may be helpful for understanding the halogenated carbene chemistry.