In this study, the acylation of toluene and benzene with octanoic acid catalyzed by the CeNaY zeolite shows low KT/KB rate ratio (KT/KB obtained by the competitive method of rate determination= 12) and high para/ortho isomer ratio (94% para isomer), ie, low substrate hut high positional selectivities. These observations are inconsistent with the Brown selectivity rules which predict that low substrate selectivity is accompanied by little ...