Thermochemical properties from ab initio calculations: π- and σ-Free radicals of importance in soot formation: •C3H3 (propargyl), •C4H3, •C13H9 (phenalenyl), •C6H5 (phenyl), •C10H7 (naphthyl), •C14H9 (anthryl), •C14H9 (phenanthryl), •C16H9 (pyrenyl), •C12H7 (acenaphthyl), and •C12H9 (biphenylyl)

✍ Scribed by Michel J. Rossi

• Publisher: John Wiley and Sons
• Year: 2008
• Tongue: English
• Weight: 285 KB
• Volume: 40
• Category: Article
• ISSN: 0538-8066
• DOI: 10.1002/kin.20326

✦ Synopsis

Abstract

The calculated difference in the standard heat of formation Δ Δ~f~H°(298.15) of n‐ and i‐C~4~H~3~^•^ free radicals is 37.9 kJ mol^−1^ for G3MP2B3 and 45.0 kJ mol^−1^ for CCSD(T)‐CBS (W1U) calculations, which seems to preclude the direct even‐carbon radical pathway to benzene and higher PAH (polycyclic aromatic hydrocarbon) formation including soot in a hydrocarbon flame. For the phenyl‐type σ‐radicals listed in the title, absolute values of Δ~f~H°(298.15) have been calculated using G3MP2B3‐computed values of bond dissociation energies D°(298.15) and combined with experimental values of Δ~f~H° (298.15) for the parent hydrocarbon because of a slight systematic overprediction of the thermodynamic stability of large PAHs by the applied computational G3MP2B3 method. Standard enthalpies of formation Δ~f~H°(298.15) as well as absolute entropies S° and heat capacities C°~p~ are given for a series of π‐ and σ‐free radicals important to combustion as a function of temperature. A spread of roughly 40 kJ mol^−1^ in the average CH bond strength of PAH leading to σ‐radicals has been calculated, the lowest leading to 4‐phenanthryl (463.6 kJ mol^−1^), the highest leading to 2‐biphenylyl radical (502.5 kJ mol^−1^). © 2008 Wiley Periodicals, Inc. Int J Chem Kinet 40: 395–415, 2008