Hyperfine Splittings in the Paramagnetic Resonances of Free Radicals

Weissman, S. I.; Townsend, Jonathan; Paul, Donald E.; Pake, G. E.

doi:10.1063/1.1698823

Cited by 61 publications

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“…Since the early days of EPR spectroscopy, it has been a point of focal interest to interpret the HFCs of organic radicals [6][7][8][9][10][11][12] and transition metal complexes. [13,14] For quantum chemistry, the HFC is a difficult property.…”

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Performance of modern density functional theory for the prediction of hyperfine structure: meta-GGA and double hybrid functionals

2007

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. Performance of modern density functional theory for the prediction of hyperfine structure: meta-GGA and double hybrid functionals. Molecular Physics, Taylor & Francis, 2008, 105 (15-16) AbstractThe performance of modern density functionals for the prediction of molecular hyperfine couplings is investigated for a series of small radicals and transition metal complexes. Besides the established BP86 (GGA) and B3LYP (hybrid) functionals we have tested two prototypical members of emerging classes of density functionals, namely the TPSS meta-GGA functional (together with its hybrid version TPSSh) and the B2PLYP double-hybrid functional. The latter is the first member of a 'fifth-rung' density functional that incorporates a fraction of orbital dependent nonlocal correlation energy estimated at the level of second order many-body perturbation theory. Since this approach is non-variational, it becomes necessary to derive and implement the so-called 'relaxed' densities in order to properly predict hyperfine couplings. The necessary formalism is described in some detail and the new method has been implemented into the ORCA electronic structure program. The results of extended test calculations reveal that TPSS is superior to BP86. The hybrid variant TPSSh is at least as accurate or better than the B3LYP functional and significantly superior to the nonhybrid TPSS variant. The B2PLYP functional also leads to accurate predictions and is a clear improvement for the difficult metal nucleus HFCs. However, it also showed a few significant outliers in the test set which points to a somewhat reduced stability in the method. The latter effect is largely attributed to the elevated fraction Hartree-Fock exchange (53%) and to some extent also to the perturbative correction.

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Performance of modern density functional theory for the prediction of hyperfine structure: meta-GGA and double hybrid functionals

2007

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“…Larger 7i-perimeters of this kind, the so called [njannulenes, mostly require bridging groups or intervening triple bonds to achieve sufficient degree of planarity and rigidity (118). Typical examples of [n]annulene derivatives with n obeying the Huckel rule of stability are l,6-methano [10]annulene (9), 1,6:8,13-bridged [14]annulenes 10 and 11, 10a,10b-dimethyl-10a,10b-dihydropyrene (12), and bisdehydro[n]annulenes with n = 14,18,22, and 26 (13). The radical ions of alkyl-substituted benzenes (16,23,26,65,111,119) and of [n]annulene derivatives (23,38,61,64,118,(120)(121)(122)(123) have been extensively studied by EPR spectroscopy since 1958 (16) and 1964 (38), respectively.…”

Section: Moderate Electron Acceptors and Donorsmentioning

confidence: 99%

“…Stone (12), H.C. Longuet-Higgins (13), E. Wasserman (14), G. Giacometti (20); 3 rd row, standing: D.D. Eley (2), K. Mobius (largely hidden, 3), J.H.…”

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Organic Radical Ions as Studied by Epr Spectroscopy

Gerson¹

1998

Foundations of Modern EPR

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“…The electron spin resonance spectra of various hydrocarbon mono-negative and mono-positive ions [1] and of the hydrocarbon radicals triphenylmethyl [2] and perinaphthenyl [3] display a well-resolved hyperfine pattern, which is due to the interaction between the magnetic moments of the electrons and the protons. This hyperfine interaction requires a finite electron spin density at the protons of the odd electron system, which according to McConnell [4] and Weissman [5] arises from the interaction between the a-electrons of the carbon-hydrogen bond and the 7r-electrons.…”

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confidence: 99%

Electron spin densities in alternant hydrocarbon mononegative and mono-positive ions and in odd alternant hydrocarbon radicals

Hoijtink

1958

Molecular Physics

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A comparison is made between MO calculations of electron spin densities in alternant hydrocarbon mono-negative and mono-positive ions and in odd alternant hydrocarbon radicals. For the positive and negative ions the I{fickel MO treatment leads to satisfactory results, whereas for radicals configuration interaction must be taken into account. In a preliminary communication McConnell and Chesnut (see ref [14]) also noticed the necessity of Tr-w interaction in the MO calculations of electron spin densities of hydrocarbon free radicals. In this way negative spin densities are found for those carbon atoms in the radical at which in the non-bonding MO the electron densities are zero. This difference between alternant ions and radicals is due to the fact that in the singly charged ions the odd electron (' positive hole ') may approximately be considered to move in the electrostatic field of the neutral carbon atoms of the hydrocarbon molecule, whereas in odd alternant hydrocarbon radicals the odd electron forms an integral part of the neutral system. INTRODUCTIONThe electron spin resonance spectra of various hydrocarbon mono-negative and mono-positive ions [1] and of the hydrocarbon radicals triphenylmethyl [2] and perinaphthenyl [3] display a well-resolved hyperfine pattern, which is due to the interaction between the magnetic moments of the electrons and the protons. This hyperfine interaction requires a finite electron spin density at the protons of the odd electron system, which according to McConnell [4] and Weissman [5] arises from the interaction between the a-electrons of the carbon-hydrogen bond and the 7r-electrons. As these authors have shown the electron spin density

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Hyperfine Splittings in the Paramagnetic Resonances of Free Radicals

Cited by 61 publications

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Performance of modern density functional theory for the prediction of hyperfine structure: meta-GGA and double hybrid functionals

Performance of modern density functional theory for the prediction of hyperfine structure: meta-GGA and double hybrid functionals

Organic Radical Ions as Studied by Epr Spectroscopy

Electron spin densities in alternant hydrocarbon mononegative and mono-positive ions and in odd alternant hydrocarbon radicals

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