Gas-phase reactions of F– with phenyl acetates. Translational energy and substituent effects on product distribution

Abstract

The gas-phase ion/molecule reactions of F^– with MeCO₂C₆H₄Y (Y = H,o-, m-, p-Me, pMeO, p-F, p-Cl) has been studied by Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry and is shown to yield two main products, YC₆H₄O^–(HF) and YC₆H₄O^–. The solvated ion is the most abundant product except for the p-Cl compound which reacts to give almost equal abundances of the two ions. The contribution of the free phenoxide ion increases significantly with increasing translational energy of the reactant F^– ion. The strong translational energy dependence of the product distribution, and its invariance upon deuterium substitution in the methyl group, suggest that both products originate primarily from a common elimination mechanism. The trend in the product-ion distribution is consistent with the observation that formation of the free YC₆H₄O^– ions from the intermediate complex is favoured by dynamical reasons when the internal energy is sufficient to overcome the endothermicity of the process. The product distributions also show a correlation with the overall free energy changes.