Rate constants for the reactions of hydroxyl radicals and chlorine atoms with halogenated aldehydes

Rate constants for the reactions of OH radicals and chlorine atoms with halogenated aldehydes of the type CX 3 CHO (X=H, Cl, or F) have been determined at 298±2 K. The OH radical rate data were determined using a pulsed laser photolysis resonance fluorescence technique at total pressures in the region 15-100 Torr and a conventional photolytic relative rate technique at atmospheric pressure. The chlorine atom rate data were determined using the relative rate method only. The rate data for reaction with both OH radicals and chlorine atoms indicate that increasing halogen atom substitution decreases the rate constant for reaction. Evidence is presented which suggests that the deactivation of these compounds is due mainly to polar effects in the transition states of the reactions induced by the halomethyl substituents, rather than decreassed overall reaction enthalpy