Ideal gas thermodynamic properties (∆H f°298 , S°2 98 , and C p (T), 300 e T/K e 1500) for 34 cyclic oxygenated hydrocarbons are calculated using the PM3 method, including 12 species on which data are not previously reported. Enthalpies of formation obtained using PM3 are further corrected by -1.642 + 0.882∆H f°298,PM3 , which is obtained by comparison to experimentally-determined ∆H f°298 of 10 cyclic oxygenated hydrocarbon molecules. Enthalpies of formation (∆H f°298 , in kcal mol -1 ) and entropy (S°2 98 , in cal mol -1 K -1 ) for 12 species are calculated as follows: -57.24 and 64.10 for 1,3-dioxetane, 25.08 and 61.36 for dioxirene, -4.62 and 68.16 for 1,2-dioxolene, -49.03 and 66.11 for 1,3-dioxolene, 16.72 and 68.21 for 1,2,3-trioxolene, -32.96 and 73.79 for 1,2-dioxane, -11.45 and 75.07 for 3,4-dihydro-1,2-dioxin, -57.44 and 72.62 for 2,4-dihydro-1,3-dioxin, -59.82 and 73.30 for 1,2,4-trioxane, -13.05 and 74.80 for 1,2,3-trioxane, -38.08 and 74.68 for 1,2,4-trioxene, and 9.14 and 74.68 for 1,2,3-trioxane, respectively. ∆H f°298 of seven molecules is different from previously estimated values by more than 4 kcal mol -1 . Our recommended ∆H f°298 values (in kcal mol -1 ) are: dioxirane (-2.47), 1,2-dioxetane (-6.38), 2,3-dihydrofuran (-23.52), 2,5-dihydrofuran (-20.90), 1,2-dioxolane (-27.42), 1,2,4-trioxolane (-59.12), and 3,6-dihydro-1,2-dioxin (-9.80). The standard deviations of ∆H f°298 and S°2 98 values determined in the present study are evaluated as 2.89 kcal/mol and 1.15 cal mol -1 K -1 . Group Additivity ring corrections for corresponding heterocyclics are derived.
