Substituent Effects on the Gas Phase Stabilities for Benzylic Anions

Abstract

It is essentially important to understand fundamental concept of electronic effects from substituents to ionic centers for both controlling reactions and designing molecules. Aromatic carbocations are first stabilized or destabilized by inductive effects of every substituents, followed by stabilization by resonance effect of para-pi-electron-releasing substituents. These behaviors of ring substituents are well described by the Yukawa-Tsuno equation. In this paper, substituent effects of carboanionic systems are investigated in gas phase in order to make clear the intrinsic effects of the substituents. According to the Yukawa-Tsuno equation, significant resonance stabilization is expected in para-pi-electron attracting substituents. We used proton transfer reaction to determine the relative stabilities of benzylic anions. Electronic energies of species in these reactions were calculated by means of DFT method. The gas phase stabilities of benzylic anions with various alpha-substituents are available from the ICR experiment, and the experimental delta-G values can be reproduced precisely by the calculated delta-E values. We compared substituent effects on delta-E of these benzylic anions with one another, to discuss electronic effects of ring substituents in carboanionic systems.