Energetics of proton transfer between carbon atoms (H3CH - CH3)−

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Abstract
Ab initio calculations were carried out to study the potential energy surface of (H3CHCH3)−. The 6–31G* basis set is supplemented by a set of diffuse p functions on both C and H (with a range of exponents for the latter). The binding energy of CH4 and CH3− to form the (H3CHCH3)− complex is about 2 kcal/mol, much smaller than for comparable ionic H‐bonded systems involving O or N atoms. Nearly half of this interaction energy is due to correlation effects, computed at second and third orders of Møller‐Plesset perturbation theory. Correlation is also responsible for substantial reductions in the energy barrier to proton transfer within the complex. This barrier is computed to be 13‒15 kcal/mol at the MP3 level, depending upon the exponent used for the H p functions.