The Selectivity of Charged Phenyl Radicals in Hydrogen Atom Abstraction Reactions with Isopropanol

Jing, Linhong; Guler, Leonard P.; Pates, George O.; Kenttämaa, Hilkka I.

doi:10.1021/jp802257m

Cited by 13 publications

(17 citation statements)

References 39 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…A similar relationship between the reaction efficiency and EA also exists for the other hydrogen-atom donor studied: isopropanol (note that for this hydrogen-atom donor, the dominant hydrogen-atom abstraction site is the α-carbon atom52). A plot of the reaction efficiency for hydrogen-atom abstraction from isopropanol versus EA for the twenty-three aryl radicals, a – w , is shown in Figure 3.…”

Section: Resultssupporting

confidence: 59%

Correlation of Hydrogen-Atom Abstraction Reaction Efficiencies for Aryl Radicals with their Vertical Electron Affinities and the Vertical Ionization Energies of the Hydrogen-Atom Donors

2008

Self Cite

View full text Add to dashboard Cite

The factors that control the reactivities of aryl radicals toward hydrogen-atom donors were studied by using a dual-cell Fourier-transform ion cyclotron resonance mass spectrometer (FT – ICR). Hydrogen-atom abstraction reaction efficiencies for two substrates, cyclohexane and isopropanol, were measured for twenty-three structurally different, positively-charged aryl radicals, which included dehydrobenzenes, dehydronaphthalenes, dehydropyridines, and dehydro(iso)quinolines. A logarithmic correlation was found between the hydrogen-atom abstraction reaction efficiencies and the (calculated) vertical electron affinities (EA) of the aryl radicals. Transition state energies calculated for three of the aryl radicals with isopropanol were found to correlate linearly with their (calculated) EAs. No correlation was found between the hydrogen-atom abstraction reaction efficiencies and the (calculated) enthalpy changes for the reactions. Measurement of the reaction efficiencies for the reactions of several different hydrogen-atom donors with a few selected aryl radicals revealed a logarithmic correlation between the hydrogen-atom abstraction reaction efficiencies and the vertical ionization energies (IE) of the hydrogen-atom donors, but not the lowest homolytic X – H (X = heavy atom) bond dissociation energies of the hydrogen-atom donors. Examination of the hydrogen-atom abstraction reactions of twenty-nine different aryl radicals and eighteen different hydrogen-atom donors showed that the reaction efficiency increases (logarithmically) as the difference between the IE of the hydrogen-atom donor and the EA of the aryl radical decreases. This dependence is likely to result from the increasing polarization, and concomitant stabilization, of the transition state as the energy difference between the neutral and ionic reactants decreases. Thus, the hydrogen-atom abstraction reaction efficiency for an aryl radical can be “tuned” by structural changes that influence either the vertical EA of the aryl radical or the vertical IE of the hydrogen atom donor.

show abstract

Section: Resultssupporting

confidence: 59%

Correlation of Hydrogen-Atom Abstraction Reaction Efficiencies for Aryl Radicals with their Vertical Electron Affinities and the Vertical Ionization Energies of the Hydrogen-Atom Donors

2008

Self Cite

View full text Add to dashboard Cite

show abstract

“…24 The higher the EA of the radical, the faster are the reactions predicted to be. This has been found to be true for many reactions.…”

Section: Resultsmentioning

confidence: 99%

“…Hence, favorable polarization of the transition state appears to be a crucial controlling factor in these reactions. 24 Consequently, radicals with widely different EA values, ranging from 3.31 eV to 6.18 eV (Chart 2), were chosen for this study. The vertical EAs of the radicals were calculated earlier at the (U)B3LYP/6–31+G(d) level of theory.…”

Section: Resultsmentioning

confidence: 99%

“…A similar finding was reported earlier for ethanol. 24a However, a correlation has been reported in the literature for isopropanol (less electrophilic radicals are more selective for hydrogen atoms bound to the α-carbon). 24b …”

Section: L-glycine and Dl-glycine-(22-d2)mentioning

confidence: 99%

“…Hence, hydrogen atom abstraction occurs also from other sites besides the α-carbon. Since abstraction of a deuterium atom is likely to be slower than of a hydrogen atom from the same site due to the primary kinetic isotope effect, 24b abstraction from the α-carbon is seemingly less favored than it actually is.…”

Section: L-glycine and Dl-glycine-(22-d2)mentioning

confidence: 99%

See 2 more Smart Citations

Reactivity and Selectivity of Charged Phenyl Radicals toward Amino Acids in a Fourier Transform Ion Cyclotron Resonance Mass Spectrometer

et al. 2011

Self Cite

View full text Add to dashboard Cite

The reactivity of ten charged phenyl radicals toward several amino acids was examined in the gas phase in a dual-cell Fourier-transform ion cyclotron resonance (FT-ICR) mass spectrometer. All radicals abstract a hydrogen atom from the amino acids, as expected. The most electrophilic radicals (with a greater calculated vertical electron affinity (EA) at the radical site) also react with these amino acids via NH2 abstraction (a nonradical nucleophilic addition-elimination reaction). Both the radical (hydrogen atom abstraction) and nonradical (NH2 abstraction) reaction efficiencies were found to increase with the electrophilicity (EA) of the radical. However, NH2 abstraction is more strongly influenced by EA. In contrast to an earlier report, the ionization energies of the amino acids do not appear to play a general reactivity controlling role. Studies using several partially deuterium-labeled amino acids revealed that abstraction of a hydrogen atom from the α-carbon is only preferred for glycine; for the other amino acids, a hydrogen atom is preferentially abstracted from the side chain. The electrophilicity of the radicals does not appear to have a major influence on the site from which the hydrogen atom is abstracted. Hence, the regioselectivity of hydrogen atom abstraction appears to be independent of the structure of the radical but dependent on the structure of the amino acid. Surprisingly, abstraction of two hydrogen atoms was observed for the 3-nitro-5-dehydrophenyl pyridinium radical, indicating that substituents on the radical not only influence the EA of the radical but also can be involved in the reaction. In disagreement with an earlier report, proline was found to display several unprecedented reaction pathways that likely do not proceed via a radical mechanism but rather by a nucleophilic addition-elimination mechanism. Both NH2 and 15NH2 groups were abstracted from lysine labeled with 15N on the side-chain, indicating that NH2 abstraction occurs both from the amino terminus as well as from the side-chain. Quantum chemical calculations were employed to obtain insights into some of the reaction mechanisms.

show abstract

Radical Chemistry in the Gas Phase

Alcaraz

Fischer

Schröder

2012

Encyclopedia of Radicals in Chemistry, Biology and Materials

View full text Add to dashboard Cite

We discuss the role of isolated radicals in various chemical environments, such as combustion engines, low‐temperature plasmas, planetary atmospheres, and interstellar space. Several methods to generate radicals are presented, for example, pyrolysis, photolysis, discharges, chemical reactions, and neutralization–reionization mass spectrometry. The breadth of each method is illustrated and species generated by these methods are introduced. It is shown that photoionization is an important tool to detect radicals and unravel their reactions. However, the often small Franck–Condon‐factors have to be considered when interpreting photoionization data. Selected results on the unimolecular and bimolecular reactions of radicals are discussed with the intention to show the scope of present methods to study radical chemistry in the gas phase. Among these methods are time‐resolved laser spectroscopy, mass‐spectrometric techniques such as charge‐tagging and schemes based on detecting radicals with synchrotron radiation.

show abstract

The Selectivity of Charged Phenyl Radicals in Hydrogen Atom Abstraction Reactions with Isopropanol

Cited by 13 publications

References 39 publications

Correlation of Hydrogen-Atom Abstraction Reaction Efficiencies for Aryl Radicals with their Vertical Electron Affinities and the Vertical Ionization Energies of the Hydrogen-Atom Donors

Correlation of Hydrogen-Atom Abstraction Reaction Efficiencies for Aryl Radicals with their Vertical Electron Affinities and the Vertical Ionization Energies of the Hydrogen-Atom Donors

Reactivity and Selectivity of Charged Phenyl Radicals toward Amino Acids in a Fourier Transform Ion Cyclotron Resonance Mass Spectrometer

Radical Chemistry in the Gas Phase

Contact Info

Product

Resources

About