NMR studies of complexes of N-methylmorpholine betaine with some benzoic acids

Ten crystalline complexes of N-methylmorpholine betaine with some benzoic acids (pKa from 0.65 to 4.85) have been synthesized and analyzed by 1H and 13C NMR spectroscopy in DMSO-d6 solution. 1H and 13C screening constants for complexes and benzoic acids and energies of complex formation have been calculated at the B3LYP/6-31G(d,p) level of theory. The linear correlations between the experimental proton and carbon chemical shifts and computed screening constants have been obtained, which allows an assignment of all resonance signals to the corresponding atoms.