Valence-bond Isomer Chemistry. Part 10.l Kinetics and Thermodynamics of the Thermal Gas-phase lnterconversion of Hexakis(penta-fluoroethy1)benzene and its para-Bonded (' Dewar ') Isomer

Equilibrium and kinetic studies on the title reaction show that the two isomers (1) and (2) are interconverted by a reversible unimolecular reaction, and lead to values for the enthalpy and entropy differences of the two isomers and activation parameters for their interconversion.

Abstract-Kinetics of the addition of thiourea to 2,6-dibenzylidenecyclohexanone and its derivatives have been studied. The reaction is found as a pseudo-first order process which includes a nucleophilic attack by thiourea at the carbonyl group of the ketone system to produce the heterocyclic pyrimidine thione "thiopyrimidine" (Claisen route mechanism). The effect of the substituents at the para position of the 2,6-dibenzylidenecyclohexanone and its derivatives on the rate of reaction, at different temperatures, is studied. Arrhenius parameters, entropies, enthalpies and free energies of activations are estimated. A suitable mechanism, which is correspondent with the results and with Claisen routes mechanism, is suggested for this reaction. IndexTerms-2,6-dibenzylidenecyclohexanone and its derivatives, mechanism route, kinetics study, thiourea, thiopyrimidine.

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