IDEAL-GAS THERMODYNAMIC PROPERTIES OF OXYGEN HETEROCYCLIC-COMPOUNDS .2. 6-MEMBERED, 7-MEMBERED AND 8-MEMBERED RINGS

The available structural parameters, fundamental frequencies and enthalpies of formation for tetrahydro-2H-pyran, 3,4-dihydro-2H-pyran, 3,6-dihydro-2H-pyran, 1,3-dioxane, 1,4-dioxane, 3,6-dihydro-1,2-dioxin, 2,3-dihydro-1,4-dioxin, 1,4-dioxin, 1,3,5-trioxane, oxepane, oxepin, 1,3-dioxepane, 4,7-dihydro-1,3-dioxepin, oxocane, 1,3-dioxocane, 1,3,6-trioxocane and 1,3,5,7-tetraoxocane were critically evaluated and the recommended values were selected. Molecular constants and enthalpies of formation for some of the molecules were estimated, because experimental values for these compounds were not available. Using the rigid-rotor harmonic-oscillator approximation, this information was utilized to calculate the chemical thermodynamic functions C-degrees p, S-degrees, -(G-degrees - H-degrees 0)/T and H-degrees - H-degrees 0 and the properties of formation DELTA(f)H-degrees, DELTA(f)G-degrees and log K-degrees(f) to 1500 K in the ideal gas state at a pressure of 1 bar. The contributions to the thermodynamic properties of 1,4-dioxin undergoing inversion motion have been computed by employing a partition function formed by the summation of the inversional energy levels. These energy levels were calculated by solving the wave equation using a potential function of type V(x) = ax4 + bx2. Thc calculated values of the thermodynamic functions are compared with those reported in other work. Agreement with experimental data, where such are available, is satisfactory within the experimental uncertainties. Thermodynamic properties for 13 compounds are reported for thc first time.