¹H, ^{1 3}C, and ^{1 5}N Chemical shifts and ¹H-^{1 5}N and ^{1 3}C-^{1 5}N heteronuclear spin-spin coupling constants in the NMR spectra of 5-substituted furfural oximes

Abstract

The ¹H, ¹³C, and ¹⁵N NMR spectra of ¹⁵N-enriched 5-substituted furfural oximes were investigated. It was shown that the chemical shifts of the ring atoms and the oxime group correlate satisfactorily with the F and R substituent constants, whereas their sensitivity to the effect of the substituents is lower than in monosubstituted furan derivatives. The constants of spin-spin coupling between the ring protons and the oxime group were determined. An analysis of the ¹H-¹H spin-spin coupling constants (SSCC) on the basis of their stereospecificity indicates that the E isomers have primarily an s-trans conformation in polar dimethyl sulfoxide, whereas the Z isomers, on the other hand, have an s-cis conformation. The signs of the direct and geminal ¹³C-¹⁵N SSCC were determined for 5-trimethylsilylfurfural oxime.