Thermodynamic Properties of Twenty-One Monocyclic Hydrocarbons

Abstract

The available structural parameters, fundamental frequencies, and relative energies of different stable conformers, if any, for cyclopropane, cyclopropene, cyclobutane, cyclobutene, 1,3-cyclobutadiene, cyclopentane, cyclopentene, 1,3-cyclopentadiene, cyclohexane, cyclohexene, 1,3-cyclohexadiene, 1,4-cyclohexadiene, cycloheptane, cycloheptene, 1,3-cycloheptadiene, 1,3,5-cycloheptatriene, cyclooctane, cyclooctene, 1,3-cyclooctadiene, 1,5-cyclooctadiene, and 1,3,5,7-cyclooctatetraene were critically evaluated and the recommended values selected. Molecular constants for some molecules were estimated as the experimental values for these compounds are not available. This information was utilized to calculate the ideal gas thermodynamic properties C○p, S○, −(G○−H○0)/T, H○−H○0, and log Kf from 100 to 1500 K. The thermal functions were obtained using the rigid-rotor harmonic-oscillator approximation. The contributions derived for the inversion motion of cyclobutane and cyclopentene were obtained from energy levels calculated with the potential functions. For cyclopentane the pseudorotational contributions to thermal functions were calculated by assuming the pseudorotation as the free rotation of the molecule. The calculated values of the thermal functions are compared with those reported in other work. Agreement with experimental data, where such are available, is satisfactory within the experimental uncertainties.