Reaction of hydrogen atoms with halogeno-methanes. Part 3.—Chloroform deuterochloroform and bromodichloromethane

Abstract

The reaction of hydrogen atoms with chloroform, deuterochloroform and bromodichloromethane has been investigated. The mechanisms of the reactions are similar to those discussed in parts 1 and 2 only the reactions are complicated by the occurrence of hydrogen (or deuterium) abstraction as well as halogen-atom abstraction. The initially formed trihalogenomethyl and dihalogenomethyl radicals combine with hydrogen atoms to form vibrationally excited halogenomethanes. From the results it has been possible to compare the relative rates of abstraction of hydrogen and halogen and to deduce the fate of the different vibrationally excited molecules.

The results of parts 1 and 2 together with the results from the present paper are combined and the following relative rates of the initial abstraction steps are deduced: (i) the relative rates of abstraction of chlorine from different halogenomethanes CCl₂Br—Cl, 1; CDCl₂—Cl, 1.2; CCl₃—Cl, 1.3; CCl₂F—Cl, 2.0; (ii) the relative rates of halogen (or hydrogen) abstraction from the same molecule k_Br/k_Cl, 1.5–1.6; k_H(D)/k_Cl, 3.3–3.4; k_Cl/k_F, 4.7. In a similar way the stabilization/decomposition ratios of the various vibrationally excited molecules are compared.