Theoretical study on the mechanism of the 1CHCl+NO reaction

The complex doublet potential energy surface of the CHClNO system, including 31 minimum isomers and 84 transition states, 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 the singlet CHCl with NO. Various possible isomerization and dissociation channels are probed. The initial association between (CHCl)-C-1 and NO at the terminal N-site can almost barrierlessly lead to the chainlike adducts HClCNO a (a(1), a(2)) followed by the direct Cl-extrusion to product P-9 Cl + HCNO, which is the most feasible channel. Much less competitively, a (a,, a2) undergoes a ring-closure leading to the cyclic isomer c-C(HCl)NO d followed by a concerted Cl-shift and N-O cleavage of d to form the branched isomers ClNC(H)O f (f(1), f(2)). Eventually, f (f(1), f(2)) may take a direct H-extrusion to produce P-7 H + ClNCO or a concerted 1,2-H-shift and Cl-extrusion to form P-1 Cl + HNCO. The low-lying products P-2 HCl + NCO, P-3 Cl + HOCN, P-14 HCO + (NCl)-N-3, P-6 ClO + HCN, and P-13 ClNC + OH may have the lowest yields observed. Our calculations show that the product distributions of the title reaction are quite different from those of the analogous (CHF)-C-1 + NO reaction, yet are similar to those of another analogous (CH2)-C-3 + NO reaction, The similarities and discrepancies among the three reactions are discussed in terms of the substitution effect. The present article may assist in future experimental identification of the product distributions for the title reaction and may be helpful for understanding the halogenated carbene chemistry. (C) 2002 Wiley Periodicals, Inc.