Structure and proton-acceptor ability of 2-phenyl-, 2-(2-furyl)-, 2-(2-thienyl)-5-phenyloxazoles and their carbonyl derivatives

IR spectroscopy and semiempirical quantum-chemical calculations were used to study the basicity of 2-phenyl-, 2-(2-furyl)-, 2-(2-thienyl)-5-phenyloxazoles and their carbonyl derivatives on H-bond formation with phenol. The furyl and thienyl radicals compared with 2-phenyl reduce the proton-acceptor ability of the oxazole nitrogen. The basicity by the carbonyl group is much lower than by the nitrogen atom. The resulting data are interpreted in terms of the steric and electronic structures of the bases and their complexes with phenols.