14N and15N NMR spectra of 2-substituted 5-nitrofurans

The¹⁴N and¹⁵N NMR spectra of a number of 2-substituted 5-nitrofurans were studied. On the basis of experimental data it was concluded that there is considerable π-electron density on the nitrogen atom of the nitro group. A linear relationship between the chemical shifts in the¹⁴N NMR spectra and the frequencies of the asymmetrical deformation vibrations of the nitro group in the IR spectra was found for the series of investigated 5-nitrofurans. The observed¹⁵N-H spin-spin coupling constants showed that in the 5-nitrofuran molecule transmission of spin information through the ring oxygen atom to the H₂ nucleus is appreciably greater than through the carbon atom to the H₄ nucleus. It was established by measurement of the¹⁵N NMR spectra that the crude adduct formed in the nitration of furfural diacetate with acetyl nitrate is a mixture of trans and cis isomers of 5-nitro-2-acetoxy-2,5-dihydrofurfural diacetate in a ratio of 7∶1. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 741–743, June, 1980.