The kinetics of the reaction between triphenylphosphine, dialkyl acetylenedicarboxylates and pyrrole in dry organic solvents at different temperatures have been studied spectrophotometrically. The observed overall second rate constant (k
2) for reaction decreases with
decreasing solvent dielectric constant and media temperature; k
2 follows the Arrhenius equation, and the overall reaction is first order in both the dialkyl acetylenedicarboxylate and triphenylphosphine concentrations. The proposed mechanism has been evaluated, and the activation
≠ and ΔH
≠ for the first, rate-determining step, as an elementary reaction have been determined on the basis of Eyring equation. In addition, the Z- and E-isomers have been optimized
at HF and B3LYP levels with the 6-311++G** basis set; the more stable is the E-isomer, in agreement with experimental data. Furthermore, to better understand the intramolecular interactions, atoms in molecules (AIM) calculations and natural population analysis (NPA) methods have been
carried out. The 1H, 13C, and 31P NMR data of these ylides are consistent with results obtained from theoretical calculations.
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Z AND E ISOMERS
Document Type: Research Article
Publication date: 2012-09-01
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Progress in Reaction Kinetics & Mechanism is an international journal for the quarterly publication of both in-depth reviews and research articles.
In-depth reviews are comprehensive accounts bringing together work from many sources with the aim of providing an article of lasting value that will become established as the reference source in the particular subject. Research articles, on the other hand, normally focus on a relatively new or recently developed field or technique giving a state-of-the-art account of the subject and may well refer to a narrower range of existing work. It covers the fields of kinetics and mechanisms of chemical processes in the gas phase and solution of both simple and complex systems.
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