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.