Intramolecular Hydrogen Bonding in α-Keto- and α-Alkoxy-carboxylic Acids. VII. Ultraviolet Spectra of Phenylglyoxylic Acid in Various Solvents

Abstract The ultraviolet spectra of phenylglyoxylic acid were determined in various solvents as well as in the mixtures of solvents. A very remarkable hypsochromic shift with increase in intensity was observed when the solvent participates in the formation of hydrogen bond as a hydrogen acceptor. The measurement of the spectra in binary mixtures of the solvents shows that the hypsochromic shift is due to the formation of a 1:1 complex of C6H5COCOOH···solvent type. This hypsochromic shift is interpreted by the destruction of the chelate ring formed by the intramolecular hydrogen bond which enforces the acid molecule to the planar conformation. This view is supported by the simple LCAO-MO calculation on this molecule.