STRUCTURAL AND SOLVENT EFFECTS UPON DECARBOXYLATION OF 2,6-DISUBSTITUTED BENZOYLOXYL RADICALS - A LASER FLASH-PHOTOLYSIS STUDY OF BIS(2,6-DISUBSTITUTED-BENZOYL) PEROXIDES

The rate constants for decarboxylation of 2,6-dimethylbenzoyloxyl, 2,4 ,6-trimethylbenzoyloxyl and 2,6-dichlorobenzoyloxyl radicals are large r than those of benzoyloxyl, 4-methylbenzoyloxyl and 2-chlorobenzoylox yl radicals, respectively,in carbon tetrachloride and acetonitrile; ho wever, the values in the former solvent are significantly larger than those in the latter. The rate acceleration with the ortho substituents is ascribed to a nonplanar geometry of the radicals brought about by twisting of the carbonyloxyl group due to a steric effect of the subst ituents. The polar solvent serves to stabilize a twisted charge-transf er structure of the radicals and retards their decarboxylation.