Determination of the 2,3-pentadienedioic acid enantiomer interconversion energy barrier 1. Classical kinetic approach
✍ Scribed by Pavel Májek; Janka Mydlová; Jan Krupcík; Jozef Lehotay; Daniel. W. Armstrong; F. Albert Cotton
- Publisher
- John Wiley and Sons
- Year
- 2006
- Tongue
- English
- Weight
- 908 KB
- Volume
- 29
- Category
- Article
- ISSN
- 1615-9306
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✦ Synopsis
Abstract
A classical kinetic method was used to determine the energy barrier for the interconversion of 2,3‐pentadienedioic acid enantiomers. Each individual enantiomer was isolated by collecting the appropriate peaks from the HPLC enantiomeric separation, of racemic 2,3‐pentadienedioic acid. The isolated enantiomers were racemized at 22°C using various interconversion times. The ratio of enantiomers in each reaction solution was determined by HPLC at 22°C. The corresponding peak areas of the enantiomers and the interconversion times obtained from the HPLC chromatograms were used to calculate both the interconversion rate constants describing (+) → (–) and (–) → (+) interconversions as well as the energy barriers. It was confirmed that the interconversion of 2,3‐pentadienedioic acid enantiomers is a first‐order kinetic reaction. Both semiempirical and ab initio methods were used to explore the mechanism of the interconversion of 2,3‐pentadienedioic acid enantiomers, and to calculate the interconversion energy barrier. Comparison of the interconversion energy barriers found by the ab initio method (Δ__G__^#^ = 110.7 kJ/mol) and by classical kinetics in the mobile phase solution at 22°C (Δ__G__^app^ = 93.9 ± 0.2 kJ/mol) shows a difference which may be attributed to the different conditions assumed in the theoretical calculation (i. e., a gaseous state) and the actual experimental conditions (i. e., liquid solution) and a possible catalytic effect of the solution composition.