The Mechanism of the Gas-Phase Ion−Molecule Reaction between Al+ and Ethanol

Abstract

The reaction between a ground-state aluminum cation and a single ethanol molecule has been investigated by computational chemistry. The structures and relative energies of reactants, intermediates, products, and transition states have been examined employing density functional theory (DFT) methods. The data are compared to those from Hartree−Fock (HF), Møller−Plesset perturbation (MP), and Gaussian [G1, G2, G2(MP2), G2(QCI)] calculations. According to recent gas-phase experiments, the low-energy collision between Al+ and ethanol results solely in the formation of Al(H2O)+ and ethylene. The present study confirms that Al+ (1S) and ethanol react to yield Al(H2O)+ and ethylene as the dominant products at thermal energies. Three different reaction paths have been considered, among them, an oxidative-addition and reductive-elimination mechanism. The reaction proceeds via an aluminum-cation-catalyzed, one-step syn elimination with a cyclic transition state. The relative energy of this transition state is similar to or below that of the entrance channel and lower than that of the highest of the other pathways. On the basis of these results, a new elimination reaction mechanism is introduced: Induced by an electrophile, one-step syn elimination takes place via a cyclic transition state following a second-order kinetic (EE2) mechanism.