Theoretical Determinations of the Ambient Conformational Distribution and Unimolecular Decomposition of n-Propylperoxy Radical

Abstract

The conformational distribution and unimolecular decomposition pathways for the n-propylperoxy radical have been generated at the CBS-QB3, B3LYP/6-31+G and mPW1K/6-31+G levels of theory. At each of the theoretical levels, the 298 K Boltzmann distributions and rotational profiles indicate that all five unique rotamers of the n-propylperoxy radical can be expected to be present in significant concentrations at thermal equilibrium. At the CBS-QB3 level, the 298 K distribution of rotamers is predicted to be 28.1, 26.4, 19.6, 14.0, and 11.9% for the gG, tG, gT, gG', and tT conformations, respectively. The CBS-QB3 C-OO bond dissociation energy (DeltaH298 K) for the n-propylperoxy radical has been calculated to be 36.1 kcal/mol. The detailed CBS-QB3 potential energy surface for the unimolecular decomposition of the n-propylperoxy radical indicates that important bimolecular products could be derived from two 1,4-H transfer mechanisms available at T< 500 K, primarily via an activated n-propylperoxy adduct.

Low temperature n-butane oxidation skeletal mechanism, based on multilevel approach

“…These values are in a good agreement with corresponding values 34.4 kcal/mol and 36.4 kcal/mol, obtained by Jungkamp et al [14] for n-butane, and value 34.8 kcal/mol for n-C 3 H 7 O 2 , obtained by Merle et al in [29] and for value 34.0 kcal/mol at 0 K in CH 3 CH 2 OO, obtained by Carstensen et al in [24].…”

Enthalpies of Formation and Bond Dissociation Energies of Lower Alkyl Hydroperoxides and Related Hydroperoxy and Alkoxy Radicals

“…These conclusions are in concordance with current views of hyperconjugation stabilizing the resultant carbon-centered radical and thus weakening the C-X bond. 55 53 In other cases the uncertainties in the literature values are so large that it is more difficult to come to any firm conclusion except that there is good agreement with the Knyazev and Slagle values and, not unexpectedly, with CBS-QB3 computations by Merle et al 44 Finally the alkyl-OOH bond energies have been computed as before, Table 10, with the alkyl formation enthalpies taken from Table 8 and our results for ROOH to yield column a and the direct computations from the reported CBS enthalpies at 298.15 K in columns b and c. Literature values are not only scarce but are quite uncertain and seemingly inconsistent. We note that our values indicate a strengthening of the C-OOH bond with increasing methyl substitution at the R-carbon, 288 f 296 f 303 f 307, whereas lengthening the carbon chain does not affect the bond energy.…”

Effects of Olefin Group and Its Position on the Kinetics for Intramolecular H-Shift and HO2 Elimination of Alkenyl Peroxy Radicals

“…45 CBS-QB3 has been widely used to explore peroxy radical chemistry. 28,29,[46][47][48][49] In CBS-QB3 calculations, the B3LYP/6-311G(d,p) zero-point energy (ZPE) is scaled by a factor 0.99; for the RRKM calculations the vibrational frequencies were scaled by a factor of 0.97. 49 The nature of saddle points was checked by vibrational analysis.…”

“…[9][10][11][12][13][14][15][16][17][18][19][20][21] A number of studies have treated larger alkylperoxy radicals. [22][23][24][25][26][27][28][29][30][31][32][33] A recent review by Taatjes illustrates how real-time spectroscopic monitoring, combined with quantum chemistry and statistical rate theory, has confirmed and extended the conclusions of older experimental work that was largely based on product yield analyses. 27 Although there is substantial literature on the fundamental chemistry of peroxy radicals derived from saturated hydrocarbon species, researchers have only very recently carried out similar investigations for peroxy radicals from biodiesel fuel (or models thereof).…”