Comparative study of kinetics isomerization of substituted polyacetylene (Cl, F, Br and I): Semi empirical RM1 study

The newly semi empirical RM1 was used to investigate the interconversions of substituted (F, Cl, Br and I) polyacetylene conformers in the vapor phase. The rates of this geometrical isomerization have been measured and the Arrhenius parameters evaluated. In the case of unsubstituted polyacetylene as the reference, the Arrhenius parameters obtained are A1 = 1.73. 1012 s−1 and Ea = 0.40 kcal mol−1. The values of the equilibrium constant for the reaction have also been determined at various temperatures between 300 and 1000 K, and the value of the energy change calculated. The results also suggest that the straightforward kinetics characterizes the majority of substituted polyacetylene isomerizations above 300 K. The isomerization energies are positive, and the barrier heights ΔEbarrier are expected to be sensitive for the magnitude of halogen effects. According to geometry features the cis→trans isomerization in the gas phase is found to be influenced by the size and electronic character of substituted halogens.