RRKM Calculated Unimolecular Reaction Rates for Chemically and Thermally Activated C2H5Cl, 1,1-C2H4Cl2, and 1,2-C2H4Cl2

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Abstract
The RRKM theory of unimolecular reactions has been applied to the HCl elimination reactions of C2H5Cl, 1,1‐C2H4Cl2, and 1,2‐C2H4Cl2, in both chemical and thermal activation systems. The experimental data are adequately represented by a model which employs a four‐center transition state. For example, the model for C2H5Cl gives a pre‐exponential factor of 1.14×1013 compared to the experimental value of 0.97×1013. The calculated and experimental nonequilibrium rate constants for C2H5Cl formed by combination of CH3 and CH2Cl radicals are 1.7×109 and 2.6×109 sec−1, respectively. Various models for the molecule were investigated in an attempt to represent the torsional degree of freedom of the molecule and its interaction with over‐all rotation. Also several models for the activated complex were studied. For the present data, the conclusions presented are as follows: (1) RRKM theory with all internal degrees of freedom taken as active, satisfactorily reproduces the observed data for these four‐center elimination reactions; (2) the torsional degree of freedom can be adequately represented as a low‐frequency vibration and the over‐all rotational degree of freedom about the ``figure axis'' need not be considered active. The activated complex models developed in this work are significantly different from the models developed by Benson and Haugen for the empirical calculation of activation energies for the H—X+olefin reactions.