Abstract
We present a detailed study of the molecular conformations, vibrational spectra and thermochemistry of the CF2(OH)CF2OONO2 and CF3CF2OONO2 peroxynitrates. In addition, we studied the CF2(OH)CF2OO, CF2(OH)CF2O, CF3CF2OO and CF3CF2O radicals, formed by the rupture of ON and OO bonds of the above peroxynitrates. The geometric structures of the most stable conformations were determined by density functional theory calculations. At the B3LYP/6-311++G(3df,3pd) level of theory, both peroxynitrates present dihedral angle COON values of about 104°. At the best levels of theory employed, G3(MP2)B3 and G4(MP2), the standard enthalpies of formation at 298K derived from isodesmic reactions, are −265.6, −248.6 and −248.5kcalmol−1 for CF2(OH)CF2OONO2, CF2(OH)CF2OO and CF2(OH)CF2O respectively; while for CF3CF2OONO2, CF3CF2OO and CF3CF2O the values of −268.2, −252.6 and −251.9kcalmol−1 were obtained. Bond dissociation enthalpies of 25.1 and 35.0kcalmol−1 have been predicted for the first time for CF2(OH)CF2OONO2 and CF2(OH)CF2OONO2 and of 23.7 and 34.2kcalmol−1 have been estimated for CF3CF2OONO2 and CF3CF2OONO2. The obtained result of the dissociation enthalpy of CF3CF2OONO2 is in excellent agreement with the available experimental determination. Therefore, the ON bond fission is the primary thermal dissociation pathway for both studied peroxynitrates.
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