1H and13C NMR spectra of 2-substituted 5-nitrofurans and conformation of chemotherapeutic preparations of the 5-nitrofuran series

The¹H and¹³NMR spectra of t-nitrofuran and 17 2-substituted 5-nitrofurans were investigated. The Δ¹H and Δ¹³C substituent increments Δ = δ(2-X-5-nitrofuran) δ(5-nitrofuran)] in the spectra of these compounds were analyzed by comparison with the analogous 5-methylfuran and furan derivatives, and the change in the sensitivity of the chemical shifts of the ring protons and the carbon atoms to the effects of substituents X as a function of the electronic character of substituent R was also analyzed. The chemical shifts and the spin-spin coupling constants were used to determine the preferred orientation of the substituents relative to the furan ring. It was found that medicinal preparations of the 5-nitrofuran series (5-nitrofurfurylidenehydrazones) exist in the form of s-trans conformers in solutions in dimethyl sulfoxide and water, whereas furagin has primarily the structure of the E s-trans form. Translated from Khimiya Geterotsiklichesklkh Soedinenii, No. 2, pp. 167–176, February, 1980. The authors thank N. O. Saldabol, M. A. Trushule, and K. K. Venter for providing us with samples of the compounds, the synthesis of which has been described in the literature.