The cracking reaction pathways and mechanisms of ethylcyclohexane and 1cyclohexyloctane with a rare earth Y (REY) catalyst were studied. Experiments at 500Β°C indicated that the dominant reactions were ring opening with subsequent secondary cracking, cracking in the alkyl side chain, isomerization, and hydrogen transfer. A kinetic model of the catalytic cracking of 1-cyclohexyloctane was developed using a novel mechanism-based lumping scheme that exploits the chemical similarities within reaction families. The formal application of 17 reaction family matrices, which correspond to 13 reaction family classes, to the matrix representations of the reactants and derived products generated the model. The reaction family concept was further exploited to constrain the kinetics within each reaction family to follow a quantitative structure/reactivity Polanyi relationship. Ultimately, nine Polanyi relationship parameters and three coking/deactivation parameters were determined by optimizing the model fit to the experimental data. The resulting model correlations were excellent, as the overall parity between experimental and model values was with a correlation coefficient of 0.971.