A relationship between the kinetics and thermochemistry of proton transfer reactions in the gas phase

For the proton transfer reaction [MH](+) + B --> M + [BH](+) (T) a correlation is observed between the experimental reaction rate k(exp) and the standard free energy variation Delta G degrees. This correlation may be described by a relationship of the type k(exp)/k(coll) = 1/[1 + exp(Delta G degrees + G(a) degrees)/RT] where k(coll) is the collision rate constant and Delta G(a) degrees an apparent energy barrier for reaction (I). It is found that Delta G(a) degrees is of the same order as RT and thus the preceding relationship allows the determination of unknown gas-phase basicities. Implications for the use of the ''bracketing'' and the ''kinetic'' methods are discussed.