The Limiting High Temperature Rotational Partition Function of Nonrigid Molecules IV. Ethylene, Propylene, 1-Butene, Cis and Trans 2-Butene, Isobutene, Trimethylethylene, Tetramethylethylene and Butadiene V. Equilibrium Constants for Reactions of Paraffins, Olefins and Hydrogen

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Abstract
IV. Methods previously developed by Eidinoff and Aston and by the writer are used to calculate the limiting high temperature rotational partition function and hence the translation‐rotation entropy for the substances named in the title. The results are compared with third law values wherever possible. The agreement is fairly good in most cases, but the calculated values probably yield more accurate structural entropy differences. V. A consistent set of frequencies for methane, ethane, propane and butane is selected, and the corresponding vibrational contributions to —F/T and H/T are tabulated. Equilibrium constants for the dehydrogenation reactions of ethane, propane, normal and isobutane are calculated and compared with experimental values. Systematic deviations are found which would be removed if the experimental equilibrium constants were reduced by a factor of 3, if the experimental hydrogenation heats were reduced by 1500 cal., or if the vibrational contribution to —F/T at reaction temperatures were 2.5 cal./deg. greater for an olefin (excluding the torsional frequency) than for the corresponding paraffin. Approximate equilibrium constants are calculated for the reactions 2C2H4=C4H8, CH4+C2H4=C3H8, CH4+C3H6=C4H10 and C2H6+C2H4=C4H10.

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