The molecular structure of gaseous tetrafluoro-p-benzoquinone and tetramethyl-p-benzoquinone as determined by electron diffraction

Schei, H.; Hagen, Kolbjørn; Trætteberg, M.; Seip, Ragnhild

doi:10.1016/0022-2860(80)85230-6

Cited by 21 publications

(18 citation statements)

References 17 publications

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“…The values of these parameters are given in Table 3, column 2, and are based on a C-6-C-7 bond length of 1.339Å. 3 In ZLI 1132 and ZLI 1695 phases, seven independent observables were available to determine the six structural and orientational parameters. The system of equations is therefore weakly overdetermined.…”

Section: Results and Discussion R A Structure Of P-tetrafluorobenzoqumentioning

confidence: 99%

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Structure ofp-tetrafluorobenzoquinone: interaction with nematic liquid crystals

Arfaoui¹,

Haloui²

2000

Magn. Reson. Chem.

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The orientation of p‐tetrafluorobenzoquinone in four nematic liquid crystals with different aromaticities was determined by measuring the fluorine– fluorine and the fluorine– carbon scalar and dipolar couplings. Signs of the J(F,F) and the J(C,F) were determined without ambiguity. The experimental geometry was compared with those obtained by diffraction techniques and by ab initio molecular orbital calculations. Assuming a solvent– solute interaction potential based entirely on dispersion forces does not agree with experimental observations. The discrepancies are partly due to the formation of charge‐transfer molecular complexes. This latter contribution was confirmed by UV spectrophotometric measurements. Copyright © 2000 John Wiley & Sons, Ltd.

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Section: Results and Discussion R A Structure Of P-tetrafluorobenzoqumentioning

confidence: 99%

“…The electron diffraction and x-ray structures of this molecule are available. 3 A partial NMR investigation into the geometry, chemical shift anisotropies and J couplings of this molecule has also been reported. 4 In the first part of this paper, we present and discuss the geometry deduced from dipolar couplings.…”

Section: Introductionmentioning

confidence: 99%

Structure ofp-tetrafluorobenzoquinone: interaction with nematic liquid crystals

Arfaoui¹,

Haloui²

2000

Magn. Reson. Chem.

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“…Further, the C(1)-C(7) bond distance is 1.35 Å in 2f and 1.34 Å in 2d, slightly shorter than that reported for the C=C double bond in duroquinone (1.352 Å). 19 The distance from the metal to the center of the h 4 -bonded carbons of the o-quinone methide ligand is 1.71 Å in 2f and 1.76 Å in 2d, and that from the metal to the h 5 -bonded Cp* ligand is 1.83 Å in 2f and 1.84 Å in 2d. The uncoordinated part of the o-quinone methide ligand is bent away from the metal, as shown by the dihedral angle of the 'hinge' across C(3) and C(6) which is 25° in 2f and 33° in 2d.…”

Section: Synthesis and Structural Characterizationmentioning

confidence: 99%

“…Following purification, the related benzenediselenol complex [Cp*Ir{h 6 -C 6 H 4 -1,4-(SeH) 2 }](BF 4 ) 2 (19) was obtained in 93% yield as a paleyellow microcrystalline solid. Compound 19 was characterized by spectroscopy ( 1 H NMR and IR); the 1 H NMR spectrum of 19 recorded in CD 3 CN contained a singlet at d 2.11 ppm attributable to the methyl protons of h 5 -Cp*Ir and another singlet at d 7.15 ppm that may be assigned to the four aromatic protons (Scheme 9).…”

Section: Synthesis and Structural Characterizationmentioning

confidence: 99%

Metal-Stabilized o-Quinone Methides, Thioquinones, and Selenoquinones: Trapping Important Reactive Intermediates and Beyond

Amouri¹

2011

Synlett

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Quinone methides (quinomethanes) act as important intermediates in organic syntheses, as well as in chemical and biological processes. However, examples of such isolated species are scarce owing to their high reactivity. Other important reactive intermediates are thio-and selenoquinones. However, unlike quinones, they are highly unstable and consequently do not exist in nature, hence their chemical and biological properties remain unknown. In this account, we describe the first isolation of the above important reactive intermediates, by p-coordination to a (pentamethylcyclopentadienyl)iridium (Cp*Ir) moiety, and their X-ray molecular structures. Further, the reactivity of such trapped intermediates is reported. For instance, the metalated o-quinone methide underwent an unusual cycloaddition reaction compared with the free o-quinone methide, while the metalated thioquinones were successfully used as organometallic linkers (OM-linkers) to construct luminescent coordination assemblies. The anticancer activity of the selenoquinone metalated complex was studied, together with related oxygen and sulfur analogues, and remarkably it was shown to be the only cytotoxic compound with a comparable activity to cisplatin.

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“…Although many papers have been published on the electrochemical behavior of various quinone derivatives, there are only few reports on the electrochemical behavior of TFQ in aqueous solution. 8,16,17 In continuing our studies of quinones, [4][5][6] we now report the electrochemical behavior of tetrafluoro-p-quinone, TFQ, in an aqueous solution at bare and activated glassy carbon electrodes (BGCE and AGCE). Thermodynamic parameters of the electrochemical reaction of TFQ have been evaluated experimentally and theoretically in this work.…”

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confidence: 97%

Thermodynamic Parameters and Electrochemical Behavior of Tetrafluoro-p-Quinone in Aqueous Solution

Yousofian-Varzaneh

Zare

Namazian

2015

J. Electrochem. Soc.

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The electrochemical behavior of tetrafluoro-p-quinone, TFQ, at bare and activated glassy carbon electrodes (BGCE and AGCE) was studied in aqueous solution by cyclic voltammetry. The effects of scan rate, pH and concentration on the electrochemical behavior of TFQ indicate that the reduced form of TFQ (tetrafluoro-p-hydroquinone, TFHQ) is adsorbed weakly at the AGCE surface whereas the oxidized form does not show any adsorption at this surface. The temperature dependency of the TFQ redox potential has been used for determination of the changes of entropy, enthalpy and Gibbs free energy of the electrochemical reaction of TFQ. Theoretical calculations have been also carried out by means of standard ab initio modern composite methods (G3B3 and G4 theories). Theoretical and experimental values for the standard redox potential of TFQ are in good agreement with each other.Quinone-hydroquinone redox systems have been studied widely because they play significant roles in different areas such as antitumor therapeutics and storage of energy. 1-7 Quinone redox reactions are sensitive to conditions of electrode surface, molecular structure and nature of substituents. 5-8 Electronegative substituents such as fluorine are known to enhance reactivity of molecules in different reactions. 9 Compounds containing fluorine are widely used as intermediate products for synthesizing pesticides, drugs, dyes and monomers for polymeric materials. 10 Tetrafluoro-p-quinone, TFQ, (Scheme 1), is an important molecule and has many applications in chemistry. 11 It is used as a photo-excited electron acceptor 12 and as a π-acceptor for the determination of some anti-inflammatory drugs such as mesalazine and antiemetic drugs such as metoclopramide. 13-15 TFQ, as a π-electron acceptor, usually forms colored charge-transfer complexes with some donor drugs which provides the possibility of their quantitative determination by spectrophotometric methods. [13][14][15] The chemical and electrochemical properties of TFQ are affected by four strongly electronegative fluorine atoms and one can expect significant changes for this species compared to the compound without fluorine atoms (phydroquinone). Although many papers have been published on the electrochemical behavior of various quinone derivatives, there are only few reports on the electrochemical behavior of TFQ in aqueous solution. 8,16,17 In continuing our studies of quinones, 4-6 we now report the electrochemical behavior of tetrafluoro-p-quinone, TFQ, in an aqueous solution at bare and activated glassy carbon electrodes (BGCE and AGCE). Thermodynamic parameters of the electrochemical reaction of TFQ have been evaluated experimentally and theoretically in this work. ExperimentalTFQ and all other chemical reagents used for the preparation of the buffer solutions were reagent grade and were purchased from Merck Company and used without purification. Solutions were prepared with doubly distilled water. Buffer solutions were made from 0.1 M H 3 PO 4 and the pH was adjusted with 2.0 M NaOH. The pH measu...

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The molecular structure of gaseous tetrafluoro-p-benzoquinone and tetramethyl-p-benzoquinone as determined by electron diffraction

Cited by 21 publications

References 17 publications

Structure ofp-tetrafluorobenzoquinone: interaction with nematic liquid crystals

Structure ofp-tetrafluorobenzoquinone: interaction with nematic liquid crystals

Metal-Stabilized o-Quinone Methides, Thioquinones, and Selenoquinones: Trapping Important Reactive Intermediates and Beyond

Thermodynamic Parameters and Electrochemical Behavior of Tetrafluoro-p-Quinone in Aqueous Solution

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