Basicity of Phenyl-Substituted 1,3-Oxazoles

Phenyl substituents in positions 2, 4, and 5 of the oxazole ring exert different effects on the electronic structure of the heteroring, which are reflected in the basicity constants of isomeric phenyl-substituted oxazoles and in changes of the spectral patterns on protonation. The calculated (AM1) gas-phase proton affinities and energies of ionization of isomeric methyl-, phenyl-, and methylphenyloxazoles were correlated with the experimental pKBH+ values. In acid medium specific solvation of phenyloxazoles is possible with participation of the heterocyclic fragment.