Hydrogen bonded networks of methoxy-substituted alpha-phenylcinnamic acidsstudied by spectroscopic and computational methods

Measurements by infrared (FT-IR) spectroscopy revealed that in solutions of low concentration the major structure forming force (short-range ordering) between methoxy-substituted alpha -phenylcinnamic acid stereoisomers was t he C=O . . .H-O intermolecular hydrogen bonding between the carboxylic grou ps. Under 10(-3) mol/dm(3) concentration no other secondary intermolecular interaction was found. In solid state, using IR spectroscopy, FT-IR and C-1 3 NMR spectroscopies, it was possible to detect (aromatic)C-H . . .O hydrog en bonds, which were thought to be responsible for long-range ordering. Thr ough the comparison of C-13 chemical shifts in the liquid phase and the sol id state (olefinic)C-H O interactions were sought for. Such interactions co uld not be found for the methoxy derivatives. Molecular modeling provided s tructural semiquantitative information for the hydrogen bonds detected by I R spectroscopy and gave additional proof for the existence of (aromatic)C-H . . .O and the non-existence of (olefinic)C-H . . .O hydrogen bonds. (C) 2 001 Elsevier Science B.V. All rights reserved.