Quantum Chemical and RRKM Investigation of the Elementary Channels of the Reaction C₆H₆ + O (³P)

Abstract

We performed a computational study of an important reaction in the combustion of hydrocarbons, C 6 H 6 , + O ( 3 P), using ab initio and RRKM methods. Density functional theory (B3LYP) was used to optimize geometries and obtain molecular vibrational frequencies, and complete basis set extrapolation (CBS-QB3) was used to obtain the energies for the reactants several transition states and products. The initial formation of a stabilized adduct is characterized by a barrier of 4.9 kcal mol -1 , in good agreement with the measured activation energy for this reaction. All product channels originate from rearrangement or decomposition of this adduct, which our calculations suggest is a triplet ground state. All of our ab initio calculations are thus conducted on the triplet surface. There are several products that are energetically accessible at combustion temperatures, but the formation of phenoxy radical, C

Products of the Benzene + O(3P) Reaction

“…It can be formed also directly from isomerization of the initial triplet adducts followed by dissociation on the triplet surface. 35 We view the latter mechanism to be unlikely, considering that this triplet PES lies significantly higher than the singlet surface, and that the ISC is expected to be facile. Regardless, the weak signal measured from the cyclopentadienyl radical precludes the possibility to examine its production in greater detail.…”

“…Hodgson et al. 35 carried out CBS-QB3 and Rice-Ramsperger-Kassel-Marcus (RRKM) calculations for reaction R1 on the triplet surface and suggested that the formation of phenoxy + H• and formylcyclopentadiene is dominant at low temperatures, while the decomposition of formylcyclopentadiene to form the cyclopentadienyl radical and HCO• is significant towards high temperatures. They also concluded that rearrangement of the C 6 H 6 O adduct to form phenol is unimportant at all temperatures.…”

A Mononuclear Cyclopentadiene–Iron Complex Grafted in the Supercages of HY Zeolite: Synthesis, Structure, and Reactivity

“…To clarify the actual molecular structure formed, a TPD-MS investigation of this species was carried out. No C 5 H 5 CHO fragment is detected due to the facile thermal decomposition of C 5 H 5 CHO to form cyclopentadienyl radical and CHO [49] (see Figure S 7 in the Supporting Information); other fragments of C 5 H 5 CHO, such as C 5 H 5 · , COC, C 6 H 4 O, and C 6 H 3 OC, can, however, be detected. Additionally, the C= O absorption band of some ferrocene derivatives with CpCHO, such as formylcyclopentadienyl(cyclopentadienyl)iron (CpFeA C H T U N G T R E N N U N G (CpCHO)) and formylferrocene, is also similar to that in our sample, [50] which suggests that the reaction of cyclopentadiene-iron with CO may result in the formation of C 5 H 5 CHO.…”

Investigation of the Mechanism of the Reaction between Atomic Oxygen Radical Anion and Benzene

“…Thus, the present method is suitable to investigate the title reaction system. Hodgson et al's results [30] have pointed out that a neutral oxygen atom will attach to the carbon atom via a small barrier length of CM1 is 0.110 nm, and it is very close to that of the benzene molecule; the distance between the attacked H and O atoms is 0.174 nm, just slightly shorter than a normal hydrogen bond length; meanwhile, Mulliken atomic-charge analysis suggests that the negative charge is predominantly restricted to that of the O atom. Thus, the interaction between O atom and the benzene ring in CM1 is strengthened due to the charge attractive effect.…”