Theoretical ab Initio Calculation of Entropy, Heat Capacity, and Heat Content

This study describes the theoretical ab initio calculation of entropy, heat capacity, and heat content for a series of alkanes by procedures that make no use of adjustable parameters. Frequencies calculated with the basis sets, 3-21G, 6-31G*, and 6-31G** and scaled by factors of 0.89 and 0.90 were used to obtain theoretical entropy values that agree well with reported values. Over a temperature range from room temperature to at least 800 K the differences between TΔS based on calculated and literature values of ΔS are generally less than 0.3 kcal/mol. Agreement between theoretical and experimental heat capacities and heat contents (H T 0 − H 0 0) is also good. Results for compounds that exist as mixtures of conformers give as good results as do compounds that exist as a single conformer.