Building the Potential Energy Profiles for electrocyclic and pericyclic organic reactions: cyclobutene ring opening and hydrogenation of ethene by diimide

Abstract

The primary goal of this study is to build potential surfaces of reactions, having a special focus into pericyclic reactions. Two different reactions will be studied computationally: the ring-opening of ciclobutene to cis-butadiene and the reduction of ethene to ethane by diimide. The same methodology will be used in both studies. First step is to regard the reactants and products of the reaction that are associated to a minima of the potential energy surface. The next step consists in searching over the potential surface in order to find a stationary point of first order saddle point character. This stationary point corresponds to a transition state. Finally, the reaction path is computed. The reaction path is a continuous curve on the potential energy surface joining the minima associated to the reactants and products through the transition state. A curve representing a reaction path curve ascends monotonically from reactants to the transition state and descends monotonically from the transition state to the products. It is taken as a reaction path curve the Intrinsic Reaction Coordinate proposed by Fukui (1). At first stance, the electronic energy is computed at the Hartree-Fock level (RHF). The RHF model assumes that the system can be described well by a single Slater determinant as electronic wave function. The Born-Oppenheimer approximation is taken into account throughout the study. This assumes that nuclei are static towards the electrons (whose speeds are way greater), so the positions of the nuclei are parameters not variables of the wave function. In this way the nuclei interact with electrons as they were a cloud, and not individual particles. 4 Barba Obón Ricard M. When the potential surface and the different stationary points are defined, energetic considerations will be taken, in terms of energy activation of reactions. Finally, but not included on this work since results have not been obtained yet, a brief study of tunnel effect will be considered on the two transferred hydrogen atoms in the reduction reaction. Hydrogen atoms are small particles compared with other atoms and can show this kind of quantum behavior.