Ab initio and density functional study of a caffeic acid amide

A series of ab initio and DFT calculations have been performed to study a natural compound often present in human diet, namely the amide of caffeic acid: 3-(3,4-dihydroxyphenyl)-2-propen-amide (ACA). Several molecular properties have been computed for this amide, such as potential energy profiles for internal rotation about different bonds, minimal conformer structures and corresponding vibrational frequencies. Twelve possible unlike conformations were found for ACA, adopting the amide group in all of them a non co-planar conformation. The conformational preferences of this amide are determined mainly by the degree of intra-molecular hydrogen bonding but non-bonding repulsions and conformational flexibility play also a key role. In all cases, the calculated properties are in good agreement with both experimental and theoretical data obtained for related molecular systems.