Hydrogen bonding interactions in alpha-substituted cinnamic acid ester derivatives studied by FT-IR spectroscopy and calculations

Intermolecular hydrogen bonding interactions in stereoisomeric cc-substitut ed cinnamic acid methyl esters (methyl 2,3-diphenylpropenoate, methyl 2-phe nyl-3-(2'-methoxyphenyl)-propenoate, methyl 2-(2'-methoxyphenyl)-3-phenylpr openoate and methyl-2,3-bis(2'-methoxyphenyl)-propenoate) were studied by F T-IR spectroscopy and model calculations at the semi-empirical quantum chem ical level of theory. Intermolecular hydrogen bonds of C-H...O types were f ound to be general in the solid stare, but rare in solution. In this hydrog en bond the carbon may be part of either aromatic ring or the olefinic bond . The hydrogen bond acceptor may be the carbonyl oxygen or the oxygen in th e methoxy substituent. Modeling helped in determining probable hydrogen bon ding sites and their positions and provided with approximate geometric para meters (bond lengths and angles). Pointing out differences between the ster eoisomers was also possible. (C) 2000 Elsevier Science B.V. All rights rese rved.