IDEAL-GAS THERMODYNAMIC PROPERTIES OF OXYGEN HETEROCYCLIC-COMPOUNDS .1. 3-MEMBERED, 4-MEMBERED AND 5-MEMBERED RINGS

The available structural parameters, fundamental frequencies and enthalpies of formation for oxirane, oxirene, dioxirane, oxetane, 1,2-dioxetane, tetrahydrofuran, 2,3-dihydrofuran, 2,5-dihydrofuran, furan, 1,2-dioxolane, 1,3-dioxolane, 1,2,3-trioxolane and 1,2,4-trioxolane were critically evaluated and recommended values were selected. Molecular constants and enthalpies of formation for some of the molecules were estimated, as experimental values for these compounds are not available. Using the rigid-rotor harmonic-oscillator approximation, this information was used to calculate the chemical thermodynamic functions C(p)O, S(O), -(G(O) - H0O)/T, H(O) - H0O, and the properties of formation, DELTA(f)H(O), DELTA(f)G(O), log K(f)O, to 1500 K in the ideal gas state at a pressure of 1 bar. The contributions to the thermodynamic properties of compounds having inversion motion (oxetane, 2,3- and 2,5-dihydrofuran) or pseudo-rotation (tetrahydrofuran and 1,3-dioxolane) have been computed by employing a partition function formed by the summation of the inversional or pseudo-rotational energy levels. These energy levels have been calculated by solving the wave equation using appropriate potential functions. The calculated values of the thermodynamic functions are compared with those reported in other works. Comparison with experimental data, where such are available, is also presented. The thermodynamic properties for seven of the compounds are reported for the first time.