FTIR studies of conformational isomerism in acrylates and acrylic acids

Acrylates have the possibility of existing in two heavy-atom planar structu res (s-cis and s-trans), and research has shown that in many instances thes e conformations have somewhat similar energies. In the case of monomeric ac rylic acid trapped in an inert matrix at low temperatures, two independent studies have shown that irradiation by UV light results in interconversion of the two rotamers. An interpretation of this phenomenon has been proposed in terms of hindered internal rotation about the central C-O bond. Our exp erimental observations on methacrylic acid las reported in this paper), and methyl methacrylate demonstrate that the former compound shows a behavior similar to that of acrylic acid, but that UV irradiation has no effect on t he interconversion of conformers in methyl methacrylate. An alternative mec hanism for the interconversion of the isomers in the acrylic acids involvin g proton transfer is proposed. (C) 1999 Elsevier Science B.V. All rights re served.