15N‐NMR Spectra of Azoles with Two Heteroatoms

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Abstract
The15N‐NMR spectra of azoles, with natural isotope abundance, have been measured under different experimental conditions, and chemical shifts are reported for imidazoles, pyrazoles, oxazoles, isoxazoles, thiazoles, and isothiazoles. General trends of substituent effects in this heterocyclic series are discussed based on the data of 67 substituted azoles, dihydro‐ and tetrahydroazoles.15N,1H spin‐coupling constants have been determined from spectra obtained by [1H] →15N polarizationtransfer experiments,i.e.an application of INEPT and DEPT pulse sequences. Two‐bond and three‐bond coupling constants are fully assigned and are discussed in terms of the specific pathways in azoles. The potential of structural applications of the new data is illustrated for isomeric nitro‐imidazoles and highly‐substituted pyrazoles, and in the case of ring‐chain tautomerism of 2‐substituted tetrahydrooxazoles.