ESR studies of alkyl aryl ketyl radicals

1981 ◽  
Vol 46 (13) ◽  
pp. 3264-3269 ◽  
Author(s):  
Eva Kutejová-Maťašová ◽  
Andrej Staško ◽  
Ľubomír Malík
Keyword(s):  
Spin Density ◽  
Unpaired Electron ◽  
Aromatic Nucleus ◽  
Alkyl Aryl ◽  
Marked Influence ◽  
Benzenecarboxylic Acids

Reactions of R1-substituted benzenecarboxylic acids (R1 = H, Me, Et, and t-Bu) with R2MgX (R2 = Et and n-Pr) in the presence of nickel produce ketyl radicals R1-Ar-CO.-R2. Average values of splitting constants of the protons in the aromatic nucleus are a2 = a6 = 0.48 mT, a4 = 0.53 mT, and a3, a5 < 0.12 mT. In some cases for R2 = n-Pr interaction of gamma protons is also observed with a2 = 0.04 mT. The investigated substituents R1, R2 have no marked influence on distribution of spin density of the unpaired electron.

Spin-density distributions in meso-alkyl/aryl hybrid porphyrin cation radicals

1988 ◽  
Vol 27 (8) ◽  
pp. 1510-1512 ◽  
Author(s):  
Michael Atamian ◽  
Richard W. Wagner ◽  
Jonathan S. Lindsey ◽  
David F. Bocian
Keyword(s):  
Spin Density ◽  
Alkyl Aryl ◽  
Cation Radicals ◽  
Density Distributions ◽  
Porphyrin Cation

Unpaired Electron Spin Density Distribution across Reduced [2Fe-2S] Cluster Ligands by 13Cβ-Cysteine Labeling

2017 ◽  
Vol 57 (2) ◽  
pp. 741-746 ◽  
Author(s):  
Alexander T. Taguchi ◽  
Yoshiharu Miyajima-Nakano ◽  
Risako Fukazawa ◽  
Myat T. Lin ◽  
Amgalanbaatar Baldansuren ◽  
...  
Keyword(s):  
Density Distribution ◽  
Spin Density ◽  
Electron Spin ◽  
Unpaired Electron ◽  
Spin Density Distribution ◽  
Electron Spin Density ◽  
Cysteine Labeling

Electron capture by oxyhaemoglobin: an e. s. r. study

1978 ◽  
Vol 201 (1144) ◽  
pp. 285-300 ◽  
Keyword(s):  
Electron Spin Resonance ◽  
Spin Density ◽  
Electron Capture ◽  
High Spin ◽  
Electron Spin ◽  
Unpaired Electron ◽  
Spin Resonance ◽  
Paramagnetic Centres ◽  
Oxygen Atoms

Exposure of aqueous glasses containing oxyhaemoglobin to 60 Co γ rays at 77 K gave two similar paramagnetic centres whose electron spin resonance (e. s. r.) spectra resembled those of low-spin ferric derivatives. These were shown to be formed in the α and β chains by electron capture. The use of oxygen labelled with 17 O showed the presence of two inequiva­lent oxygen atoms and it is shown that the unpaired electron has consider­able spin density on the dioxygen ligand as well as on iron. When warmed above 77 K two new paramagnetic centres were formed, possibly as a result of protonation, before the formation of normal high-spin methaemoglobin, presumably by loss of HO 2 ¯ . Oxymyoglobin gave comparable centres.

scholarly journals Isonitriles as Stereoelectronic Chameleons: The Donor-Acceptor Dichotomy in Radical Additions

2018 ◽  
Author(s):  
Gabriel dos Passos Gomes ◽  
Yulia Loginova ◽  
Sergei Vatsadze ◽  
Igor Alabugin
Keyword(s):  
Spin Density ◽  
Lone Pair ◽  
Analysis Data ◽  
Nbo Analysis ◽  
Basis Set ◽  
Dynamic State ◽  
Intramolecular Electron Transfer ◽  
Electronic Effects ◽  
Alkyl Aryl ◽  
Conformational Effects

This study started from a simple question of why isonitriles and alkynes (the two functional groups that look so much alike in their ground states) provide drastically different type of products in addition reactions. Whereas addition to alkynes proceeds in a “1,2-addition” where the new bonds are formed at the different alkyne carbons, isonitriles can react via “1,1-insertion” by forming <i>both </i>new bonds at the <i>same </i>terminal carbon of the isonitrile moiety. Such outcome is consistent with the hidden carbene nature of the isonitrile functionality. <div><br></div><div><p>Due to the ability of serving as 1,1-synthons, isonitriles lend themselves to a variety of annulations where they serve as a one-carbon component in assembly of carbo- or heterocycles (e.g., [4+1] annulations pioneered by Curran) or, with a change of reactant topology, as two-atom components in the assembly of heterocycles. </p>Our hypothesis was this behavior should be associated wtih additional state-crossings that corresponds to intramolecular charge and spin-transfer between nitrogen and carbon. Understanding of such dynamic state interconversion may unlock new electronic effects, not available to alkynes. From the practical perspective, such conceptual understanding can lead to the design of more efficient radical cascades.</div><div>Indeed, computational analysis of isonitrile's interaction with alkyl, aryl, heteroatom-substituted and heteroatom-centered radicals found a number of intriguing electronic, supramolecular and conformational effects. In general, the evolution of electronic changes in the process of radical addition to isonitriles reveals that this reaction starts and continues all the way to the TS mostly as a simple addition to a polarized pi-bond. Only at the later stages, after the TS has been passed, intramolecular electron transfer from the lone pair of carbon to the nitrogen moves the spin density to the a-carbon to form the imidoyl radical, the hallmark intermediate of the 1,1-addition-mediated cascades. </div><div><br></div><div>Computational Details:</div><div><div><div><div><p>Calculations were carried with the Gaussian 09 software package, using the (U)M06-2X DFT functional (with an ultrafine integration grid of 99,590 points) with the 6-311++G(d,p) basis set for all atoms except of Sn and Ge, for which we have used the Def2-QZVPP basis set. Grimme’s D3 version (zero damping)for empirical dispersion was also included. Frequency calculations were conducted for all structures to confirm them as either a minimum or a Transition State (TS). Intrinsic Reaction Coordinates (IRC) were determined for the TS of interest. Barriers were evaluated from isolated species due to formation of complexes for some systems, but not all of them. We performed Natural Bond Orbital (NBO) analysis on key intermediates and transition states. NBO deletions were performed at the UHF/6-311G(d) level of theory unless otherwise noted. Spin density was evaluated from the NBO analysis data. The Gibbs Free energy values are reported at 298 K, unless noted otherwise. We have used GoodVibes by Funes-Ardoiz and Paton to obtain the temperature-corrected Gibbs Free energies for calculating the temperature effects on selectivity in multifunctional substrates.</p></div></div></div></div><div><br></div>

scholarly journals Isonitriles as Stereoelectronic Chameleons: The Donor-Acceptor Dichotomy in Radical Additions

2018 ◽  
Author(s):  
Gabriel dos Passos Gomes ◽  
Yulia Loginova ◽  
Sergei Vatsadze ◽  
Igor Alabugin
Keyword(s):  
Spin Density ◽  
Lone Pair ◽  
Analysis Data ◽  
Nbo Analysis ◽  
Basis Set ◽  
Dynamic State ◽  
Intramolecular Electron Transfer ◽  
Electronic Effects ◽  
Alkyl Aryl ◽  
Conformational Effects

This study started from a simple question of why isonitriles and alkynes (the two functional groups that look so much alike in their ground states) provide drastically different type of products in addition reactions. Whereas addition to alkynes proceeds in a “1,2-addition” where the new bonds are formed at the different alkyne carbons, isonitriles can react via “1,1-insertion” by forming <i>both </i>new bonds at the <i>same </i>terminal carbon of the isonitrile moiety. Such outcome is consistent with the hidden carbene nature of the isonitrile functionality. <div><br></div><div><p>Due to the ability of serving as 1,1-synthons, isonitriles lend themselves to a variety of annulations where they serve as a one-carbon component in assembly of carbo- or heterocycles (e.g., [4+1] annulations pioneered by Curran) or, with a change of reactant topology, as two-atom components in the assembly of heterocycles. </p>Our hypothesis was this behavior should be associated wtih additional state-crossings that corresponds to intramolecular charge and spin-transfer between nitrogen and carbon. Understanding of such dynamic state interconversion may unlock new electronic effects, not available to alkynes. From the practical perspective, such conceptual understanding can lead to the design of more efficient radical cascades.</div><div>Indeed, computational analysis of isonitrile's interaction with alkyl, aryl, heteroatom-substituted and heteroatom-centered radicals found a number of intriguing electronic, supramolecular and conformational effects. In general, the evolution of electronic changes in the process of radical addition to isonitriles reveals that this reaction starts and continues all the way to the TS mostly as a simple addition to a polarized pi-bond. Only at the later stages, after the TS has been passed, intramolecular electron transfer from the lone pair of carbon to the nitrogen moves the spin density to the a-carbon to form the imidoyl radical, the hallmark intermediate of the 1,1-addition-mediated cascades. </div><div><br></div><div>Computational Details:</div><div><div><div><div><p>Calculations were carried with the Gaussian 09 software package, using the (U)M06-2X DFT functional (with an ultrafine integration grid of 99,590 points) with the 6-311++G(d,p) basis set for all atoms except of Sn and Ge, for which we have used the Def2-QZVPP basis set. Grimme’s D3 version (zero damping)for empirical dispersion was also included. Frequency calculations were conducted for all structures to confirm them as either a minimum or a Transition State (TS). Intrinsic Reaction Coordinates (IRC) were determined for the TS of interest. Barriers were evaluated from isolated species due to formation of complexes for some systems, but not all of them. We performed Natural Bond Orbital (NBO) analysis on key intermediates and transition states. NBO deletions were performed at the UHF/6-311G(d) level of theory unless otherwise noted. Spin density was evaluated from the NBO analysis data. The Gibbs Free energy values are reported at 298 K, unless noted otherwise. We have used GoodVibes by Funes-Ardoiz and Paton to obtain the temperature-corrected Gibbs Free energies for calculating the temperature effects on selectivity in multifunctional substrates.</p></div></div></div></div><div><br></div>

ESR study of anion radicals produced in cathodic reduction of 2-furfural derivatives

1979 ◽  
Vol 44 (3) ◽  
pp. 762-772 ◽  
Author(s):  
Andrej Staško ◽  
Peter Pelikán ◽  
František Tomanovič ◽  
Viliam Pätoprstý
Keyword(s):  
Nitrogen Atom ◽  
Nitro Group ◽  
Spin Density ◽  
Unpaired Electron ◽  
Indo Method ◽  
Hammett Constants ◽  
Half Wave ◽  
The Individual ◽  
Maximum Spin ◽  
Anion Radicals

Furfural and its derivatives are reduced reversibly to the corresponding anion radicals during polarography in dimethylformamide. These radicals have been studied by ESR, and analysis of their spectra has been carried out. The calculated splitting constants and half-wave potentials (INDO method) agree well with the experiment. The maximum spin density of the unpaired electron has been found for the aldehydic proton of the furfural anion (aH = 1.01 mT), the values for the remaining protons of furane ring being smaller (aH3 = 0.115 mT, aH4 = 0.49 mT, and aH5 = 0.64 mT). Introduction of nitro group in 5 position of furfural results in a marked shift of spin density of the nitrogen atom (aN = 0.533 mT) and decrease of density at the aldehydic proton (aH = 0.334 mT). Chenges of half-wave potentials of the individual furfural derivatives correlate well with changes in the respective Hammett constants of the substituents.

scholarly journals Spin Densities in Copper-Nitronyl Nitroxide Complexes

1993 ◽  
Vol 48 (1-2) ◽  
pp. 120-122 ◽  
Author(s):  
J.-X. Boucherle ◽  
E. Ressouche ◽  
J. Schweizer ◽  
B. Gillon ◽  
P. Rey
Keyword(s):  
Spin Density ◽  
Unpaired Electron ◽  
Wave Functions ◽  
Nitronyl Nitroxide ◽  
Electron Wave ◽  
Spin Populations ◽  
Spin Densities

Abstract The spin density in two copper-nitronyl nitroxide complexes, viz. bis(hexafluoroacetylacetonato)-(2,4,4,5,5-pentamethyl-l-oxy-imidazoline 3-oxide)-copper(II) and dichloro-bis(2-phenyl-4,4,5,5-tetra-methyl-l-oxy-imidazoline 3-oxide)-copper(II), has been determined by polarised-neutron diffrac-tion. Spin populations and unpaired electron wave functions have been refined.

scholarly journals Unexpected electron spin density on the axial methionine ligand in CuA suggests its involvement in electron pathways

2020 ◽  
Vol 56 (8) ◽  
pp. 1223-1226
Author(s):  
Marcos N. Morgada ◽  
María-Eugenia Llases ◽  
Estefanía Giannini ◽  
María-Ana Castro ◽  
Pedro M. Alzari ◽  
...  
Keyword(s):  
Electron Transfer ◽  
Electronic Structure ◽  
Spin Density ◽  
Electron Spin ◽  
Unpaired Electron ◽  
Axial Ligand ◽  
Electron Spin Density ◽  
Metal Site ◽  
Electron Transfer Pathways

The presence of unpaired electron spin density in the axial ligand of the CuA site suggest a new description of the electronic structure of this metal site that supports the feasibility of previously neglected electron transfer pathways.

A study of the relationships between unpaired electron density, spin-density and cumulant matrices

2010 ◽  
Vol 128 (4-6) ◽  
pp. 405-410 ◽  
Author(s):  
Luis Lain ◽  
Alicia Torre ◽  
Diego R. Alcoba ◽  
Roberto C. Bochicchio
Keyword(s):  
Electron Density ◽  
Spin Density ◽  
Unpaired Electron ◽  
Unpaired Electron Density
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