The structures and conformation of 3-methoxy-4-hydroxy-5-chloro-phenylpyruvic acid3and its acetate ester4have been investigated by X-ray crystallography and by spectroscopic methods. Three independent molecules crystallized for the ester4with the triclinic symmetry and the centrosymmetric space group (Z=6) and with the cell dimensionsa=11.764(6),b=13.549(5),c=13.978(15) Å. α=100.08(7), β=94.62(8), γ=115.06(4)°. The three conformers of4exist as the enolate tautomers and not the keto form.Transextended side pyruvic acid side chains were observed for the three conformers. The crystalline cohesion was ensured by a strong network of hydrogen bonds. The NMR spectra of the phenylpyruvic acid3and the acetate ester4exhibited each a single proton on the benzylic carbon atom and chemical shift values supporting the existence of the enolate tautomer form for these phenylpyruvic acid compounds in solu
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