Structure of vinyl ethers of a number of azoles according to1H and13C NMR data and quantum-chemical calculations

NMR¹H and¹³C spectra have been used to establish the conformational states of a number of azole vinyl ethers and to study the nature of the conjugation of the unshared pair of electrons of the oxygen atom with the azole and vinyl moieties. The H¹ NMR spectra of the vinyl ethers of indazole, 4,5-diphenylimidazole, benzimidazole, and 1,2,4-triazole revealed anomalous downfield shifts of the signal of the proton of the vinyl group, which are attributed to specific interactions, resembling weak hydrogen bonds, between these hydrogen atoms and the pyridine nitrogen. This conclusion agrees with the results of quantum-chemical calculations for the vinyl ether of indazole.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 5, pp. 1031–1036, May, 1990.