Carbon-13 magnetic resonance as a probe for solute-solvent interaction in dipolar heterocyclic media

Carbon-13 magnetic resonance shifts of solvent carbon atoms were measured as a function of solute concentration for a series of alkali metal salts inN-methyl-2-pyrrolidone and 3-methyl-2-oxazolidone, which are 5-membered dipolar-aprotic heterocyclic solvents of dielectric constants 32.0 and 77.5, respectively. Chemical shifts were linear functions of solute molarities in the concentration range of 0.19–0.75M. Cation-solvent interaction decreased in tenacity as Li⁺>Na⁺>K⁺. Shifts were anion dependent for both solvents, and the magnitude of solvent structure shielding, by solute anions, decreased as tetraphenylborate > thiocyanate > perchlorate. The carbonyl shifts ofN-methyl-2-pyrrolidone and 3-methyl-2-oxazolidone were compared to other heterocyclic solvents.