Thermochemical properties for n-propyl, iso-propyl, and tert-butyl nitroalkanes, alkyl nitrites, and their carbon-centered radicals

Density functional theory (DFT) based calculations are performed on a series of alkyl nitrites and nitroalkanes representing large-scale primary, secondary, and tertiary nitro compounds and their radicals resulting from the loss of their skeletal hydrogen atoms. Geometries, vibration frequencies, and thermochemical properties [S°(T) and C°_p(T) (10 K ≤ T ≤ 5000 K)] are calculated at the B3LYP/6-31G(d,p) DFT level. ΔfH° ₂₉₈ values are from B3LYP/6-31G(d,p), B3LYP/6-31+G(2d,2p), and the composite CBS-QB3 levels. Potential energy barriers for the internal rotations have been computed at the B3LYP/6-31G(d,p) level of theory, and the lower barrier contributions are incorporated into entropy and heat capacity data. The standard enthalpies of formation at 298 K are evaluated using isodesmic reaction schemes with several work reactions for each species. Recommended values derived from the most stable conformers of respective nitro-and nitrite isomers include-30.57 and-28.44 kcal mol^-1 for n-propane-,-33.89 and-32.32 kcal mol^-1 for iso-propane-,-42.78 and-41.36 kcal mol^-1 for tert-butane-nitro compounds and nitrites, respectively. Entropy and heat capacity values are also reported for the lower homologues: nitromethane, nitroethane, and corresponding nitrites.