SOLID-STATE STRUCTURES OF PHENYLPYRUVATES AS STUDIED BY HIGH-RESOLUTION C-13 NMR-SPECTROSCOPY

High resolution solid state C-13 NMR measurements were made on phenylpyruvic acid and its sodium, lithium and calcium salts, using the total suppression of spinning side bands and the dipolar diphasing technique. The spectra of their 2-C-13 enriched analogs were also recorded. The NMR data were discussed by reference to the solution spectra, and the following definitive evidence was obtained: the acid, the hydrated sodium and lithium sats and the dehydrated sodium salt take the enol, the diol and the keto form, respectively, but the hydrated calcium salt exists in the keto form. The C-13 NMR signal of the gem-diol carbon was found to appear at 98 ppm. The calcium salt has two doublets at 166 and 134 ppm which originate from the carbons C(1) and C(4); this splitting suggests that the carboxylate group and/or the phenyl ring in the phenylpyruvate anion are oriented in two different ways.