A Gaussian-2 and Gaussian-3 study of alkoxide anion decompositions. 1. H-2and CH4 eliminations of the methoxide, ethoxide, isopropoxide, and tert-butoxide anions

The decomposition mechanisms of four alkoxide anions, CH3O-, CH3CH2O-, (CH3 )(2)CHO-, and (CH3)(3)CO-, have been studied with modified G2 (G2++) and G3 methods. The energy profiles for the decomposition reactions of each alkox ide anion are reported. It is found that the decompositions proceed via an anionic mechanism with a stepwise pathway. For anions CH3CH2O- and (CH3)(2) CHO-, calculated results indicate that the H-2 elimination has a lower ener gy barrier than the CH4 elimination. This result is in total agreement with the experimental data obtained in the collision-activated dissociation and infrared multiple photon induced elimination studies of simple alkoxide an ions.