Absorption levels were obtained for five hydrocarbons of increasing polarity in three tetrachloroaluminate catalysts of increasing cation size. Obtained absorption levels were found to correlate with cation size and hydrocarbon polarity. Molecular modeling was used to calculate charge transfers from absorbed hydrocarbons to the catalysts. Obtained charge transfers were also found to correlate with hydrocarbon absorption levels. Lastly, polarities calculated for absorbed free-radicals suggest a mechanism for previous findings. In the previous effort, resid conversion was found to go through a maximum with increasing hydrogen tetrachloroaluminate contents in a sodium tetrachloroaluminate catalyst.