Abstract
ABSTRACT The isomerization reaction of 2-butenedioic acid in gas phase has been studied using Hartree-Fock (HF), Moller-Plesset to 2 nd order (MP2) and BLYP, B3LYP Density Functional Theory (DFT) levels of approximation. Potential energy surfaces (PES) of the singlet and triplet states of the molecule are constructed in order to corroborate the hypothesis that the reaction proceeds by a non-adiabatic path. A total of ten stationary points (eight singlet and two triplet) were characterized as energy minima or saddle points. Thermochemical analysis of the triplet conformers and singlet most stable structures yields a value of the ΔH° of activation for isomerization that is in good agreement with the expected results. Keywords: Potential energy surface; Isomerization Maleic acid; DFT calculations. e-mail address: rugarte@uach.cl 1. INTRODUCTION As is well known, substituted ethylenes exhibit cis-trans isomerism. For instance maleic acid transforms into fumaric acid at high temperatures (melting point); this transformation is often accompanied by partial descomposition. The isomerization also occurs by heating an aqueous solution of maleic acid in a sealed tube above 130° C, by catalyzing with various acids and salts at ≈ 100° C and as a result of bromine atoms.
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