Hydrogen-bonding Structures and Energetics of Acrylamide Isomers, Tautomers, and Dimers: An ab initio Study and Spectral Analysis

Hydrogen-bonding patterns and energetic profiles of acrylamide isomers (syn- and skew-), tautomers (amide and imidic acid forms) and 13 stable dimers have been studied using the second-order Moller-Plesset perturbation theory with basis sets up to aug-cc-pVTZ. Syn-acrylamide is the most stable monomer with a reaction barrier of 4.15 kcal/mol for the syn-skew isomerization reaction. The direct amide-imidic acid tautomerization reaction is separated by too high a barrier to surpass. The most stable dimer corresponds to the planar double-hydrogen-bonded configuration, indicating its crucial role in determining the stability of the formed complex. Moreover, hydrogen bonds have significant effects on the infrared spectral features, which can be consistently explained solely based on the acrylamide dimeric structures and energetics without monomeric and dimeric tautomer forms. The results are useful for studying the stability of the acrylamide clusters in condensed-phase samples such as those in food chemistry studies.