NEW THEORETICAL AND EXPERIMENTAL PROTON AFFINITIES FOR METHYL HALIDESAND DIAZOMETHANE - A REVISION OF THE METHYL CATION AFFINITY SCALE

High-level ab initio calculations and variable-temperature proton-tran sfer equilibrium constant measurements have been used to obtain new th ermochemical data for protonated halogenomethanes (CH(3)XH(+), X = F, Cl, Pr, and I) and protonated diazomethane (CH3NN+). Proton affinities of CH(3)X and CH2NN and methyl cation affinities of HX and N-2 have b een derived. The theoretical and experimental results are in good agre ement with one another but in several cases are in conflict with curre ntly accepted experimental proton and methyl cation affinities. Experi mental and theoretical methyl cation affinities are presented for a va riety of molecules, leading to the proposal of a new methyl cation aff inity scale.