Structures, internal rotor potentials, and thermochemical properties for a series of nitrocarbonyls, nitroolefins, corresponding nitrites, and their carbon centered radicals

Structures, enthalpy (Δ _fH° ₂₉₈), entropy (S°(T)), and heat capacity (C _p(T)) are determined for a series of nitrocarbonyls, nitroolefins, corresponding nitrites, and their carbon centered radicals using the density functional B3LYP and composite CBS-QB3 calculations. Enthalpies of formation (Δ _fH° ₂₉₈) are determined at the B3LYP/6-31G(d,p), B3LYP/6-31+G(2d,2p), and composite CBS-QB3 levels using several work reactions for each species. Entropy (S) and heat capacity (C _p(T)) values from vibration, translational, and external rotational contributions are calculated using the rigid-rotor-harmonic- oscillator approximation based on the vibration frequencies and structures obtained from the density functional studies. Contribution to Δ _fH(T), S, and C _p(T) from the analysis on the internal rotors is included. Recommended values for enthalpies of formation of the most stable conformers of nitroacetone cc(=o)cno2, acetonitrite cc(=o)ono, nitroacetate cc(=o)no2, and acetyl nitrite cc(=o)ono are -51.6 kcal mol ^-1, -51.3 kcal mol ^-1, -45.4 kcal mol ^-1, and -58.2 kcal mol ^-1, respectively. The calculated Δ _fH° ₂₉₈ for nitroethylene c=cno2 is 7.6 kcal mol ^-1 and for vinyl nitrite c=cono is 7.2 kcal mol ^-1. We also found an unusual phenomena: an intramolecular transfer reaction (isomerization) with a low barrier (3.6 kcal mol ^-1) in the acetyl nitrite. The NO of the nitrite (R-ONO) in CH ₃C(=O′)ONO moves to the C=O′ oxygen in a motion of a stretching frequency and then a shift to the carbonyl oxygen (marked as O′ for illustration purposes).