Abstract
Steric hindrance to solvation of pyridinium cations is largest for two α-t-butyl substituents, less for one t-butyl and one phenyl, less for two α-phenyl groups, and least for one phenyl and one alkyl. The effect of α-phenyl groups is reduced by buttressing. Gas-phase proton affinities of the pyridine determined by dimer dissociation do not correlate with the solution p
K
a
values. Steric accelerations of pyridinium dealkylation show fair correlation with solution p
K
a
; reasons for discrepancies are discussed.