Competitive photochlorination and kinetic isotope effects for hydrogen/deuterium abstraction from the methyl group in C₂H₆, C₂D₆, CH₃CHCl₂, CD₃CHCl₂, CH₃CCl₃, and CD₃CCl₃

Abstract

The abstraction of hydrogen and deuterium from ethane, 1,1-dichloroethane, 1,1,1-trichloroethane, and some of their deuterated analogs by photochemically generated ground state chlorine atoms has been investigated in the temperature range 7–95 °C using methane as competitor. Rate constants and their temperature coefficients are reported for the following reactions:[Formula: see text]An Arrhenius law temperature dependence was observed in all cases. Mixed primary and α-secondary kinetic isotope effects are k 1 /k 2 = 2.79 ± 0.27, k 4 /k 6 = 4.13 ± 0.32, k 7 /k 8 = 1.46 ± 0.12 at 298 K and decrease to k 1 /k 2 = 2.53 ± 0.22, k 4 /k 6 = 4.06 ± 0.28, k 7 /k 8 = 1.45 ± 0.09 at 370 K, showing a "normal" temperature dependence. The kinetic isotope effect for H/D abstraction from the methyl group decreases with increasing number of chlorine substituents in the adjacent chloromethyl group. The β-secondary isotope effect, k 3 /k 5 , is close to unity and shows a slight inverse temperature dependence.