KINETICS OF THE REACTIONS OF HALOGENATED METHYL RADICALS WITH MOLECULAR BROMINE

The kinetics of seven reactions of halogenated methyl radicals (CH2Cl, CHCl2, CFCl2, CF2Cl, CF3, CH2Br, and CH2I) 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 CF3 + Br2 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 Br2 (which (which includes the 7 reactions studied here and 4 C(H)x(CH3)3-x + Br2 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 effect on the reaction rate constant.