Alkylation of benzene and toluene with cinnamyl alcohol has been carried out in the presence of a series of acid Y faujasites with three levels of Na+-to-H+ exchange (HY-21, HY-50 and HY-100) and with different framework Si-to-Al ratio (HY-D1, HY-D2 and HY-D3). This system provides a good example of the possibilities of tunable acidity in zeolites to control a chemical reaction. Thus, while 1,3-diarylpropenes were the predominant reaction products using HY-21 and HY-50 catalysts, further reaction of the C=C double bond to give arylindanes and triarylpropanes takes place using the other more acidic catalysts. Finally, no detectable amounts of branched allylic isomer 3,3-diaryl-1-propene, generally also formed by attack at the three position of the cinnamyl alcohol, were observed.