The ortho effect and the additivity of substituent parameters in the reaction between phenols and poly(vinyl acetate) radicals have been investigated in the light of theories postulated by Swain and Lupton on substituent constants Fkand Rkand that of Williams and Norrington on the unique positional weighting factors fjand rj. The present correlation studies show that while Charton's theory that the ortho-substituent effect is primarily electrical is true for most of the substituents, some steric considerations have to be invoked while dealing with groups like o-tert-butyl. The additivity of fjFkand rjRkis much less satisfactory than that of Hammett's [sgrave] or Brown-Okamoto's electrophilic [sgrave]+substituent constants.