The thermochemistry of the gas phase reaction: CF 3CH 2Br+I 2=CF 3CH 2I+IBr. Polarity effects in thermochemistry

Abstract

The gas phase equilibria in the reaction CF 3CH 2Br+I 2=CF 3CH 2I+IBr have been studied over the temperature range 614–726 K. A third law treatment of the data gave Δ H° itr (298 K)=6.6±0.5 kcal mole −1. This result led to Δ° itf(CF 3CH 2Br, g, 298)= −166.0± 0.5 kcal mole −1 and DH° (CF 3CH 2Br)=69.2±1 kcal mole −1. These results were combined with previous data to obtain the enthalpies of reaction for the series. ▪ in which X=H, I, and Br. It was found that the enthalpies of reaction became progressively less negative as the electronegativity of the substituent, X, increased. These experimental enthalpy changes are shown to be in excellent agreement with the net change in electrostatic interaction energy which was calculated assuming that the CF 3 and CH 2X groups in the reactant and product molecules were polarizable dipoles. The good agreement supports the hypothesis that polarity does play an important role in gas phase thermochemistry.