A Study of Solvent Effects on the 13C Nuclear Magnetic Resonance Spectra of Cholesterol, Pyridine, And Uridine

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Abstract
The 13C n.m.r. chemical shifts for cholesterol in five solvents are reported. All carbon atoms were subject to solvent effects of varying sign and magnitude. The chemical shifts in the solvent pair dioxane–chloroform 1:1 could be predicted on an additivity basis. Pyridine was studied in 24 solvents; the chemical shifts of all carbons were solvent-dependent. Solvent effects at positions β and γ were correlated, while those at position α bore no simple relation to those of the other carbons. A small isotope effect was noted on comparing the data for H2O and 2H2O. Coupling between 13C and 14N was observed in some cases; its magnitude was solvent-dependent. Uridine was studied in four solvents. While all carbons were subject to solvent-induced shifts, evidence for specific solvent interaction at C-4, -5, -1′, and -2′ was obtained. An appreciable contribution to the relaxation of carbonyl C-2 and -4 from dipole–dipole interaction with the hydrogen on N-3 was observed. Solvent effects can result in scrambling and misassignment of 13C resonances if care is not taken with choice of solvent.

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