Electrochemistry as a tool to monitor Lewis acid-base reactions between methacrylonitrile and metallic surfaces: A theoretical and experimental proposal

This paper presents a tentative extension of the Lewis acid-base concept to the case of an organic molecule interacting with a polarized metallic surface. Towards this aim, we make use of the Density Functional Theory (DFT) viewpoint on Lewis acid-base interactions. This theory has been shown to be relevant to describe adhesion processes at a molecular scale. It allows the introduction of three key parameters, for the molecule as well as for the metallic surface. These are the DFT chemical potential, mu, the absolute hardness, eta and the Fukui function, f ((r) over right arrow). In the present paper, we show that the DFT chemical potential, mu, of the metallic surface is linearly related to the electrode potential drop, Delta epsilon, imposed between this surface and a reference electrode in an electrochemical cell. Thus, while the chemical potential of the molecule is only determined by its chemical structure, that of the metallic surface can be monitored continuously. This means that the Lewis acidic or basic character of the metallic surface towards the molecule can, in principle, be chosen. We present experimental results arguing in the sense of this model by studying the interaction of 2-methyl 2-propenenitrile (methacrylonitrile) alternatively with a metallic cathode and with a metallic anode. The two different transient molecule/surface interactions are frozen thanks to an anionic electropolymerization of the monomer on the cathode and to a (first reported) cationic electropolymerization of the monomer on the anode. A detailed analysis of the molecular structures of the two resulting polymer/metal interfaces shows results which are in agreement with the theoretical predictions. This paper is dedicated to Professor Jacques Schultz as an acknowledgement of his constant interest in our work.