Correlation between the synchronicity and thermodynamic parameters based on Hammond-Leffler postulate in the decomposition reactions of cis-3,6-dicarboxyle-cyclohexa-1,4-diene and cyclohexa-1,4-diene

Decomposition of thecyclohexa-1,4-diene(1) and cis-3,6-dicarboxyle-cyclohexa-1,4-diene(2)to hydrogen molecule and their corresponding aromatic rings have been investigated at five different (300,400,500,600 and 700k) temperatures by means ofB3LYP and M06-2X methods with the 6-311+G** basis set on all atoms and natural bond orbital (NBO) interpretations.The rate constants fitted the Arrhenius equation.Two levels of theory showed that the calculated Gibbs free energy different between the transition and ground state structures (ΔG‡) decrease from compound 1 to compound 2.the variation of the calculatedΔG‡ values can justified by the decreaseof the advancement of transition state structures (δBav)from compound 1 to 2 .Therefor the advancements of the transition state structures (δBav)exothermic charactersΔ[Gproduct –Greact ]associated withHammond-Leffler postulate.