Abstract: Aromatic compounds, such as benzene or biphenyl, are alkylated with an alkylating agent having from one to eight carbons atoms, such as propylene, in the presence of an acidic mordenite zeolite catalyst under conditions sufficient to produce a mixture of substituted aromatic compounds enriched in the linear alkylated isomers, such as p-diisopropylbenzene or p,p'-di(isopropyl)biphenyl, respectively. The novel acidic mordenite catalyst is characterized by its silica/alumina molar ratio, its porosity, and a Symmetry Index. The p,p'-disubstituted isomers of aromatic compounds are useful as monomers in the preparation of thermotropic, liquid crystal polymers.