Electrochemical oxidation of some catechol and hydroquinone derivatives has been investigated both experimentally and theoretically to bring hints into the connection of thermodynamic and oxidation potential. The theoretical results were calculated at DFT (B3LYP, BP86) levels of theory and 6-311G (p,d) basis sets. In this study we focus on the mechanisms of the electrochemical oxidation of catechol in the presence of various nucleophiles. A general thermodynamic cycle, which is proposed to calculate Delta G of oxidation of the intermediates and products, introduces thermodynamic as one of the important parameters on the reaction mechanisms. The results of this work show that electrochemical oxidation potential of studied compounds is directly dependent on the Delta G of electrochemical oxidation. Also it was found that depending on the Delta G of electrochemical oxidation, the products which are produced on the surface of electrode will participate in the electrochemical or chemical following reactions. Finally we can consider several mechanisms in the electrochemical oxidation of catechol in the presence of different nucleophiles. (C) 2013 The Electrochemical Society. All rights reserved.