A matrix isolation spectroscopic and quantum chemical study of fumaric andmaleic acid

Relative energies and vibrational spectra of buthenedioic acid [(E)- and (Z )-HOOC-CH=CH-COOH; fumaric and maleic acids] were calculated using Hartree- Fock (HF), Moller-Plesset to 2nd order (MP2), and B3LYP Density Functional Theory (DFT) levels of approximation. Computationally the lowest energy con former of maleic acid has a nearly planar structure with an OH . . .O=C int ramolecular hydrogen bond closing a seven member O=C-C(H)=C(H)-C-O-H ring. Second conformer of maleic acid adopts a cis arrangement around the C-O bon ds and exhibits the two carbonyl bonds in a nearly orthogonal arrangement w ith one carboxylic group in the plane containing the carbon atoms. Fumaric acid has three planar conformers with relative energies within 5 kJ mol(-1) . These conformers exhibit a cis arrangement around the C-O bond and differ by the relative conformation of their O=C-C=C axes. The infrared spectra o f the studied compounds isolated in a solid argon matrix feature the most s table conformers, Narrowband tunable irradiation in the near-infrared regio n (6901 cm(-1)) was found to promote a conversion of the second most stable conformer of maleic acid into the most stable conformer.