The 13C-NMR and FT-IR spectra of dicyanoacetic acid esters were measured in various solvents. Aprotic solvents such as MeCN and CHCl3 favor the structure (NC)2CHCO2R (R = Me, Et, CH2CHMe2, CH2Ph, CH2CCl3, allyl, CMe3, Ph, C6H4NO2-4), whereas solvents with good H-bond-accepting ability (DMSO, H2O, MeOH) favor the formation of enols, as shown by comparison of the 13C-chem. shifts of the enols with those of their Na or K salts. The x-ray anal. of the sodium salt of p-nitrophenyl dicyanoacetate establishes the partial double bond character of the C1-C2 bond which is the reason for the hindered rotation in salts and enols as obsd. by NMR spectroscopy.