Topological Symmetry Control in Spin Density Distribution:  Spin Chemistry of Phenalenyl-Based Neutral Monoradical Systems

Kawai, Junya; Fukui, Kozo; Nakazawa, Shigeaki; Sato, Kazunobu; Shiomi, Daisuke; Takui, Takeji; Nakasuji, Kazuhiro

doi:10.1021/ol0352097

Cited by 46 publications

(33 citation statements)

References 22 publications

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“…16 The dependence of the spin distributions on the positions of oxygen substituents has been termed "spin topological symmetry control". 35,36 The molecular orbital pictures and energy diagrams of PLY, 4OPO and 6OPO are illustrated in SOMO levels of the OPO systems compared to that of the PLY system imply high electron accepting abilities of the OPO systems. The energy gaps between the SOMO and LUMO in the OPO systems are significantly smaller than that of the PLY system, indicating multistage electron accepting abilities which may be key factors for applications as electrode active materials in secondary batteries (vide infra).…”

Section: Molecular Design and Topological Isomersmentioning

confidence: 99%

“…35 in order to isolate them as stable species in air, kinetic stabilization by steric protection at the appropriate positions is a key issue. From this viewpoint, 6OPO system with methyl substituents at the 2, 5-positions was first designed.…”

Section: -And 6-oxophenalenoxyl (4opo 6opo) Systemsmentioning

confidence: 99%

“…42 The tert-butyl group, sterically more congested group than methyl group, greatly improves the stabilities of 4OPO and 6OPO, enabling them to be handled in air. 35,43 Taking advantage of this strategy, 7-hydroxy-TB6OPO was also designed and synthesized as the first neutral radical having an intramolecular hydrogen bond coupled with an extremely delocalized spin system. 44 These neutral radicals were prepared by the methods depicted in Scheme 3.10.…”

Section: -And 6-oxophenalenoxyl (4opo 6opo) Systemsmentioning

confidence: 99%

“…35 Experimentally and theoretically (in parentheses) obtained hfccs of 1 H, spin density distributions, and hyperfine EPR spectra for (a) TB4OPO and (b) TB6OPO. (b Reprinted with permission from[43].…”

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confidence: 99%

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Phenalenyls, Cyclopentadienyls, and Other Carbon‐Centered Radicals

Nishida

2010

Stable Radicals

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Section: Molecular Design and Topological Isomersmentioning

confidence: 99%

Section: -And 6-oxophenalenoxyl (4opo 6opo) Systemsmentioning

confidence: 99%

Section: -And 6-oxophenalenoxyl (4opo 6opo) Systemsmentioning

confidence: 99%

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Phenalenyls, Cyclopentadienyls, and Other Carbon‐Centered Radicals

Nishida

2010

Stable Radicals

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“…Both quantities are commonly used as quantitative aromaticity indicators. 47,48 The aromaticity indicators were calculated for the neutral quinone, semiquinone radical anion and hydroquinone dianion both with the hydrogen atoms on the quinone ring left unsubstituted and substituted by Cl and Br.The NICS profiles for neutral quinone species are typical for nonaromatic molecules, 45 while those for hydroquinone dianions are typical for aromatic species, although notably less aromatic than the prototype benzene. The profiles obtained for semiquinone molecules are halfway between these typical cases, as one could expect on the basis of the resonance structures in Scheme 1.…”

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confidence: 99%

Stabilisation of tetrabromo- and tetrachlorosemiquinone (bromanil and chloranil) anion radicals in crystals

et al. 2011

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Crystal structures of alkali salts of tetrahaolgenosemiquinone anion radical acetone solvates and their solvent-free salts are determined. p-Semiquinone anion radical reveals enhanced aromaticity of the ring compared to the quinone. A pair of p-stacked radical anion (psemiquinone) rings occurs in crystal structures of potassium and rubidium salts of tetrachlorosemiquinone anion acetone solvates and their potassium tetrabromo analogue. The ring centroid separation distances are about 3.2 Å and carbon-carbon contacts between the contiguous rings are 0.3 Å shorter than the sum of van der Waals radii. The spin-coupling of the two unpaired electrons between the two anion radical rings (forming a stacked dimer) correlates with the diamagnetic property of the crystals. Magnetic properties of alkali salts of tetrahaolgenosemiquinone anion radical acetone solvates were examined by electron paramagnetic resonance spectroscopy. IntroductionQuinones and semiquinone radicals undergo easily reversible oxidation-reduction reactions and they are excellent electron carriers. Due to influence of the functional groups, quinones may have various values of the standard redox potential. The oxidation potential of the quinones with electron-donating groups such as -OH, is lower, and with electronwithdrawing groups such as -Cl and -NO2, the potential becomes higher. These unique electron properties of quinones are exploited for syntheses, both, in laboratory and by nature in vivo. 1,2 Substituents on the quinoid ring modify electron density affecting oxidation potential and stability of the semiquinone radical (Scheme 1). Perhalogenated benzoquinones are easily reduced and their radicals are rather stable; four electronegative substituents make electron density in the ring significantly lower. Sodium and potassium salts of tetrachlorosemiquinone anion radical were first prepared in 1912 by Torrey and Hunter 3 by reaction of alkali iodide and tetrachloroquinone in acetone. Green salts with formulae NaC 6 C l4 O 2 and KC 6 C l4 O 2 precipitated from cold acetone but quickly decomposed upon heating. During the last fifty years perhalogenosemiquinones were studied by various techniques: EPR, 4-6 UV/Vis 7 and IR/Raman spectroscopy [8][9][10][11] and computational methods. [12][13][14][15] Several charge-transfer systems involving tetrachloro-1,4-benzoquinone (Cl4Q) [16][17][18][19][20] and tetrabromo-1,4-benzoquinone (Br4Q), 21,22 where radical anions can be stabilised under appropriate conditions, have also been designed. A crystallographic study of tetrachlorosemiquinone radical anion-in its well-known potassium salt3-was attempted in a Rudjer Bo_skovi_c Institute, Bijeni_cka 54, HR-10000 Zagreb, Croatia. E-mail: kmolcano@irb.hr Molčanov, K., , "Stabilisation of tetrabromo-and tetrachlorosemiquinone (bromanil and chloranil) anion radicals in crystals", CrystEngComm, Vol.13, No.16, 1973 23 using a film method (Weissenberg camera). However, due to an extremely weak diffraction of poor crystals the authors could only determine unit cells of...

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Curved π‐Conjugated Stable Open‐Shell Systems Possessing Three‐Dimensional Molecular/Electronic Spin Structures

Ueda

2011

Fragments of Fullerenes and Carbon Nanotubes

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Topological Symmetry Control in Spin Density Distribution: Spin Chemistry of Phenalenyl-Based Neutral Monoradical Systems

Cited by 46 publications

References 22 publications

Phenalenyls, Cyclopentadienyls, and Other Carbon‐Centered Radicals

Phenalenyls, Cyclopentadienyls, and Other Carbon‐Centered Radicals

Stabilisation of tetrabromo- and tetrachlorosemiquinone (bromanil and chloranil) anion radicals in crystals

Curved π‐Conjugated Stable Open‐Shell Systems Possessing Three‐Dimensional Molecular/Electronic Spin Structures

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