Photoelectron Spectroscopy and Ion Chemistry of Benzoxazolide

Abstract

Photoelectron imaging of deprotonated benzoxazole reveals the adiabatic electron affinity of C2-benzoxazolyl σ radical EA₀ = 2.75(1) eV. This exceeds the corresponding quantity for oxazolyl by more than 0.5 eV. The extra stabilization of the benzoxazolide anion is attributed to charge sharing between the benzene and oxazole rings. By combining the measured electron affinity of the radical with the calculated acidity of the parent molecule, the C2–H bond dissociation energy of benzoxazole is determined: D₀ = 117.4(5) kcal/mol or DH₂₉₈ = 118.9(5) kcal/mol. In comparison to other closed-shell organic molecules (e.g., benzene), the increased strength of the C2–H bond in benzoxazole indicates a reduced stability of σ-benzoxazolyl due to the impeded delocalization of the radical electron within the heterocyclic part of the molecule. These results have implications for chemical reactivity (e.g., the substitution reactions) of benzoxazole and its derivatives.