Methyl Cation Affinities of Canonical Organic Functional Groups

Methyl cation affinities are calculated for the canonical nucleophilic functional groups in organic chemistry. These methyl cation affinities, calculated with a solvation model (MCA*), give an emprical correlation with the NsN term from the Mayr equation under aprotic conditions when they are scaled to the Mayr reference cation (4-MeOC6H4)2CH+ (Mayr E = 0). Highly reactive anionic nucleophiles were found to give a separate correlation, while some ylides and phosphorus compounds were determined to give a poor correlation. MCA*s are estimated for a broad range of simple molecules representing the canonical functional groups in organic chemistry. On the basis of a linear correlation, we estimate the range of nucleophilicities of organic functional groups, ranging from a C–C bond to a hypothetical tert-butyl carbanion, toward the reference electrophile to be about 50 orders of magnitude.