Geometrical Isomerism of Phenylhydrazones of α-Keto Esters. II. p-Substituted Phenylhydrazones of Ethyl Pyruvate and 2,4-Dinitrophenylhydrazones of Some α-Keto Esters

Article abstract of DOI:10.1246/bcsj.59.73

Each geometrical isomer of various substituted phenylhydrazones of ethyl pyruvate and 2,4-dinitrophenylhydrazones of some α-keto esters was isolated in a pure state.Partial isomerizations of the E-isomers of the former hydrazones to the Z-isomers took place by keeping solutions of the hydrazones in organic solvents containing C, H, and Cl in the dark.An E- or Z-structure was assigned to each molecule on the basis of IR and 1H NMR spectra.In all cases, isomers with higher R_f -values on a silica gel TLC (using benzene as a developing solvent) involved an intramolecular hydrogen bonding between the imino hydrogen and the ester carbonyl oxygen.Thus, the Z-structure was assigned.An E-structure was assigned to other isomers with lower R_f-values.The present assignment is, thus, entirely the same as that proposed in a previous investigation.