Kinetics of the reactions of halogenated methyl radicals with molecular bromine

The kinetics of seven reactions of halogenated methyl radicals (CH 2 Cl, CHCl 2 , CFCl 2 , CF 2 Cl, CF 3 , CH 2 Br, and CH 2 I) with molecular bromine were studied by using a heatable tubular reactor coupled to a photoionization mass spectrometer. Rate constants were measured as a function of temperature, typically between 296 and 532 K. Arrhenius activation energies were found to be small negative values (typically - 2 kJ mol −1 ) for all reactions studied with the exception of that of the CF 3 +Br 2 reaction (whose activation energy is positive, but which could not be determined accurately). The pattern in reactivity among 11 reactions of substituted methyl radicals with Br 2 (which includes the 7 reactions studied here and 4 C(H) x (CH 3 ) 3−x +Br 2 reactions (x=0-3) studied earlier) has been accounted for by the inductive effect of the substituent atoms or groups. The sum of the Pauling electronegativities of these substituents provides a useful measure of their total inductive effects on the reaction rate constant