Bond dissociation energies and radical heats of formation in CH3Cl, CH2Cl2, CH3Br, CH2Br2, CH2FCl, and CHFCl2

Abstract An analysis of thermochemical and kinetic data on the bromination of the halomethanes CH 4– n X n (X = F, Cl, Br; n = 1–3), the two chlorofluoromethanes, CH 2 FCl and CHFCl 2 , and CH 4 , shows that the recently reported heats of formation of the radicals CH 2 Cl, CHCl 2 , CHBr 2 , and CFCl 2 , and the CH bond dissociation energies in the matching halomethanes are not compatible with the activation energies for the corresponding reverse reactions. From the observed trends in CH 4 and the other halomethanes, the following revised Δ H ° f ,298 ( R ) values have been derived: Δ H ° f (CH 2 Cl) = 29.1 ± 1.0, Δ H ° f (CHCl 2 ) = 23.5 ± 1.2, Δ H f (CH 2 Br) = 40.4 ± 1.0, Δ H ° f (CHBr 2 ) = 45.0 ± 2.2, and Δ H ° f (CFCl 2 ) = −21.3 ± 2.4 kcal mol −1 . The previously unavailable radical heat of formation, Δ H ° f (CHFCl) = −14.5 ± 2.4 kcal mol −1 has also been deduced. These values are used with the heats of formation of the parent compounds from the literature to evaluate CH and CX bond dissociation energies in CH 3 Cl, CH 2 Cl 2 , CH 3 Br, CH 2 Br 2 , CH 2 FCl, and CHFCl 2 .