Adsorbent filters often use activated carbons to remove a wide range of toxic chemicals from air. It is of interest to know if filter performance for these compounds can be diffusion limited as a result of molecular structure effects from bulky functional groups. A concentration-swing frequency response (CSFR) technique was used to measure mass transfer rates of various C-10 hydrocarbons to explore molecular structure effects on diffusion in amorphous BPL activated carbon. The hydrocarbon adsorbates of interest were n-decane, alpha-pinene, limonene, and decalin. The fluorocarbon perfluorodecalin was also investigated. These C-10 hydrocarbons have different ring or branched shapes, but their volatilities are similar. By plotting amplitude ratios as a function of frequency and fitting to a mathematical model derived from transfer functions, CSFR can easily distinguish among different mass transfer rate mechanisms and permits the accurate calculation of diffusion coefficients. The CSFR experiment was performed at multiple gas-phase concentrations for each adsorbate, and a micropore diffusion model describes the data well. Adsorption isotherms were measured for each adsorbate on BPL activated carbon and analyzed using a pore filling model. Predicted isotherm slopes regressed from the CSFR experiments compare well with the equilibrium isotherm slopes. For each adsorbate, the measured diffusion coefficients are found to be highly concentration dependent. The order for fastest to slowest diffusing compounds is n-decane > limonene > perfluorodecalin > decalin > alpha-pinene, with alpha-pinene showing clear evidence of molecular shape factors. Quantitative structure-activity relationship (QSAR) models of the data show diffusion rates decrease in correlation with rigid ring structures.