Ionization Energies of Three Resonance-Stabilized Radicals: Cyclohexadienyl (d_n, n = 0, 1, 6, 7), 1-Phenylpropargyl, and Methylcyclohexadienyl

Abstract

The ionization energies for three resonance-stabilized radicals are determined: cyclohexadienyl, 1-phenylpropargyl, and methylcyclohexadienyl. The recommended ionization energies are, respectively, 6.820(1), 6.585(1), and 7.232(1) eV. That of cyclohexadienyl is found to be just 0.02 eV above a high level ab initio calculation [Bargholz, A.; Oswald, R.; Botschwina, P. J. Chem. Phys. 2013, 138, 014307], and that of 1-phenylpropargyl is found within the stated error of a recent experimental determination [Holzmeier, F.; Lang, M.; Hemberger, P.; Fischer, I. ChemPhysChem 2014, DOI: 10.1002/cphc.201402446]. The ionization energy of the methylcyclohexadienyl radical is consistent with the ortho isomer. Ionization energies of a range of isotopologues of cyclohexadienyl radical are given, along with their D1 ← D0 origin band positions, which indicate a blue shift of 18 cm(-1) per deuterium atom substituted. The ionization energy of cyclohexadienyl, along with the calculated bond dissociation energy of Bargholz et al., affords a new estimate of the 0 K proton affinity of benzene: 739.7 ± 2.0 kJ/mol. The ionization energies are discussed in terms of the interplay between radical and cation stabilization energies.

Quantum-Induced Symmetry-Breaking in the Deuterated Dihydroanthracenyl Radical

“…All four isomers are predicted to have similar ionization energies and, characteristic of the B3LYP/6-311+G(d,p) level of theory, the values are lower than the observed value. [33,35] For a range of resonance-stabilized radicals, Troy reported that the B3LYP/6-311+G(d,p) adiabatic ionization energies underestimated experiment by a deviation of 0.14( 7 The reported ionization energy in the text and Table 1 is corrected by +0.007 eV to account for the finite electric field in the extraction region of the spectrometer. [33] adding the 0.14 (7) eV to the calculated adiabatic energies, we obtain our best calculated estimates for the ionization energies of the various isomers.…”

Hydrogen-atom attack on phenol and toluene is ortho-directed

“…The cyclohexadienyl radical itself (H + benzene) is well characterized. [10][11][12][13] Additionally, several reports characterizing the hydronaphthyl radical (H + naphthalene) have been reported recently. [14][15][16][17][18] However, the spectroscopy, structure, energetics and kinetics of H-addition to other common aromatics, such as toluene and phenol, are largely unreported.…”

Hydrogen Atom vs. Hydride Transfer in Cytochrome P450 Oxidations: A Combined Mass Spectrometry and Computational Study

“…Because of the peculiar features of cycloheptatriene, we envisaged that a detailed gas phase reactivity study towards [Fe IV (O)(TPFPP + · )] + would be interesting, and help elucidate intrinsic factors that determine the reactivity behavior of this model of P450 Cpd I. An interesting comparison may also arise from the reaction of [Fe IV (O)(TPFPP + · )] + with 1,3‐cyclohexadiene (CHD) as it has a comparable IE and also similar C–H BDE CH for the methylene group (IE and BDE CH values are equal to 8.25 eV and 72.9 kcal mol –1 , respectively), see Table , , . However, ionization of the so‐formed radical is remarkably easier for c‐C 7 H 7 · when compared to the c‐C 6 H 7 · radical from 1,3‐cyclohexadiene (6.28 vs. 6.82 eV, respectively).…”

“…However, ionization of the so‐formed radical is remarkably easier for c‐C 7 H 7 · when compared to the c‐C 6 H 7 · radical from 1,3‐cyclohexadiene (6.28 vs. 6.82 eV, respectively). Table gives a summary of all cited thermochemical data , , …”