HYDROGEN-BONDING INTERACTIONS OF ALPHA-PHENYLCINNAMIC ACID ISOMERS IN THE LIQUID-PHASE STUDIED BY IR AND NMR SPECTROSCOPIES AND COMPUTATIONAL METHODS

Intra- and intermolecular hydrogen bonding interactions of alpha-phenylcinnamic acid isomers were studied in the solution phase by infrared (IR) and proton nuclear magnetic resonance (H-1 NMR) spectroscopies and the AM1 semi-empirical method. The solvents were CDCl3 or dimethyl sulfoxide (DMSO), the concentration of the acid isomers were varied. Spectroscopic measurements revealed that (i) intermolecular hydrogen bonds are typical for both acid isomers via their carboxylic groups (OH...O hydrogen bonding), monomer acids were only present in significant amounts at 10(-4) mol/dm(3) and (ii) CDCl3 was not involved in the aggregated structures of any isomers, while the oxygen in DMSO seemed to interact with the olefinic proton of the E isomer. Weak intramolecular hydrogen bonds could be identified computationally in the Z isomer: (aromatic)C-H...O, C=O...H, but none in the E.