Mechanisms for the breakdown of halomethanes through reactions with ground-state cyano radicals.

Abstract

One route to break down halomethanes is through reactions with radical species. The capability of the artificial force-induced reaction algorithm to efficiently explore a large number of radical reaction pathways has been illustrated for reactions between haloalkanes (CX3 Y; X=H, F; Y=Cl, Br) and ground-state ((2) Σ(+) ) cyano radicals (CN). For CH3 Cl+CN, 71 stationary points in eight different pathways have been located and, in agreement with experiment, the highest rate constant (10(8) s(-1) M(-1) at 298 K) is obtained for hydrogen abstraction. For CH3 Br, the rate constants for hydrogen and halogen abstraction are similar (10(9) s(-1) M(-1) ), whereas replacing hydrogen with fluorine eliminates the hydrogen-abstraction route and decreases the rate constants for halogen abstraction by 2-3 orders of magnitude. The detailed mapping of stationary points allows accurate calculations of product distributions, and the encouraging rate constants should motivate future studies with other radicals.