Studies on Azole-to-Azole Interconversion − An Interesting Case of Absence of a “Primary Steric Effect” in the Ring-Degenerate Equilibration betweenortho-Substituted 3-Aroylamino-5-methyl-1,2,4-oxadiazoles and 3-Acetylamino-5-aryl-1,2,4-oxadiazoles in Methanol

Abstract

Keywords: Free energy relationships / NMR spectroscopy / Oxygen heterocycles / Rearrangements / Ring-ring interconversionsThe title reaction has been studied by 1 H NMR, both in CD 3 OD and in tBuOK/CD 3 OD. The components of the electronic effect of the substituent on the benzene ring show different contributions depending on whether the equilibrium between neutral (strong prevalence of the ''proximity polar effect'') or anionic species (balance between ''ordinary and proximity polar effects'') is considered. The ''primary steric [a]