Deprotonating Molecules and Free Radicals to Form Carbon-Centered Anions: A G2 ab Initio Study of Molecular and Free Radical Acidity

摘要

Molecules CH_3H and free radicals ·CH_2X can be deprotonated to form carbon-centered anions CH_2X~- and radical anions HCX~(·-), respectively. We have studied the geometric and thermochemical changes that accompany such deprotonation processes for a variety of substituents X including the π-donor groups NH_2, OH, OCH_3, PH_2, SH, F, Cl, and Br and the π-acceptor groups BH_2, AlH_2, CHO, NO_2, CN, and NC. Thermochemical properties calculated and discussed include the gas-phase acidities of the molecules and free radicals, the electron affinities of the ·CH_2X free radicals, various dissociation energies, and the heats of formation of all species. The acidities of ·CH_2X radicals are predicted to be greater than those of CH_3X for π-donor substituents but less for π-acceptor substituents (except CN and NC). The changes that are predicted to occur upon deprotonation in C-X bond lengths, C-X homolytic and heterolytic bond dissociation enthalpies, C-H homolytic bond dissociation enthalpies, and radical stabilization energies may be understood by examining the orbital interactions that take place in each species.