The Limiting High Temperature Rotational Partition Function of Nonrigid Molecules I. General Theory. II. CH4, C2H6, C3H8, CH(CH3)3, C(CH3)4 and CH3(CH2)2CH3. III. Benzene and Its Eleven Methyl Derivatives

I. The method given by Eidinoff and Aston for calculating the limiting high temperature rotational partition function has been further simplified. An important special case, comprising molecules which may be represented by a rigid framework to which symmetrical tops are attached in any position is developed. II. The methods of the preceding part are applied to the series of methyl derivatives of methane, and to the completely nonrigid molecule n-butane. The calculated entropies at 25°C show the same general variation with chain length and number of branches as has been found experimentally from the third law. III. The entropies of all the isomeric methyl derivatives of benzene are calculated. Comparison with third law values for the liquids is hampered by lack of reliable vapor pressure data and of vibration frequencies, but there are no major discrepancies which must be attributed to either the calculated or the observed entropies.