Benzene-induced solvent shifts in the nuclear magnetic resonance spectra of substituted oxazoles

Abstract

The chemical shifts (δ) and solvent shifts (Δ=δ_CC14–δ_C6H6 p.p.m.) have been assigned for the proton resonances in 21 substituted oxazoles. Many assignments have been made using deuterium labelling and long-range spin–spin coupling. The hydrogen resonance of a substituent at the 4-position of the oxazole nucleus is either unaffected or slightly deshielded by benzene, whereas those of the 2- and 5-positions are shielded in benzene. A 1 : 1–solvent complex is proposed, and a study of the Δ values for oxazoles containing bulky alkyl substituents indicates that benzene complexes near the oxygen of the oxazole nucleus.