The kinetics of a large series of smaller alcohols and diols and bulkier terpenol molecules was studied spectroscopically in order to determine the mechanistic importance of substrate size in the rate of electrocatalyzed indirect oxidation by Ce-IV mediators. Two mediators were used: Ce-IV p-toluenesulfonate (I) and p-methoxybenzenesulfonate (II), which lead to the fast formation of a Ce-IV-substrate complex. The next oxidation step was the slow and determinant step. The electronic effects were not important since the stoichiometry of the hydroxyl ligand and the sulfonic ligands was 1/6. The difference in reactivity was due to the larger size of the terpenols. It was demonstrated spectroscopically that a Ce-III complex is formed after the oxidation step and its size is important because it needs to be continuously reoxidized at the anode to continue the catalytic process. A higher reactivity of mediator II compared to mediator I was observed and it was possibly explained by the electronic effects of their ligands because they now have a 6/1 ratio of ligands vis-a-vis the hydroxyl ligand.