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  • 1
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Octaethyltetrathiaporphyrin dication, OTP2+, is electrochemically reduced by two successive electron-transfer processes to OPT0. OPT2+ forms intermolecular complexes with a series of π-donors. The association constants of the resulting complexes are controlled by the oxidation potentials of the π-donors and solvent properties. OTP2+ was incorporated into a Nafion membrane cast on a Pt electrode. Formation of OTP2+-π-donor complexes in the polymer membrane was followed by electrochemical and spectroscopic means. The association constants of the OTP2+-π-donor complexes in the Nafion membrane exhibit lower values than a homogeneous phase owing to the high ionic strength in the polyelectrolyte.
    Additional Material: 11 Ill.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The octaethyltetrathiaporphyrin dication, OTP2+, forms 1:1 intermolecular donor-acceptor complexes with NiII-, VIVO- and FeIII-octaethylporphyrins. The association constants of the complexes are governed by the oxidation potential of the metallo-octaethylporphyrins and by secondary electrostatic interactions. Octaethylporphyrin, H2OEP, forms intermolecular complexes with OTP2+. Kinetic analyses of the formation of the various complexes revealed the formation of a primary complex exhibiting the stoichiometry (OTP2+)2(H2OEP). This intermolecular complex transforms into a thermodynamically stabilized intermolecular assembly with a stoichiometry corresponding to (OTP2+)4H2OEP. The activation barrier associated with the conversion of the primary complex to the thermodynamically stabilized assembly is Ea = 16·5 kcal mol-1 (1 kcal = 4·184 kJ). The association constant of the complex (OTP2+)2(H2OEP) is K1 = 1·3 × 1010 M-2 and the equilibrium constant between the two coexisting intermolecular complexes (OTP2+)4(H2OEP) and (OTP2+)2(H2OEP) is K2 = 7·4.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Proton hyperfine data have been determined for the radical anions and cations of dibenzo [b,f]pentalene (III) and its 5, 10-dimethyl derivative (IV). The assignment of the coupling constants to pairs of equivalent protons follows from a simple MO model, the use of which enables one to reproduce satisfactorily the experimental values. The proton hyperfine data, aHμThe meaning of aHμis aH—C(x),H—C(y),whereas only x and y are given in the particular cases., for the radical anion III⊖. correlate fairly well with the π-charge populations ∊μ derived from 1H-NMR. spectra for the carbon centres μ in the dianion III2⊖. The analogous correlation is less good in the case of the radical cation III⊕. and the dication III2⊕., presumably due to the rough approximations involved in the evaluation of the numbers ∊μ for the latter species. The coupling constants aH5,10 for III⊖. and III⊕. are very close to the corresponding values aH4,6 for the radical ions of 1,3,5-tri-t-butylpentalene (II), in accord with the prediction of the MO model. A similarity is also found between the proton hyperfine data for III⊖. and those for the radical anions of structurally related 1,4-diphenyl-1,3-butadiene (V). On the other hand, there are striking changes in the coupling constants of the analogous protons on passing from III⊖. to the radical anions of dibenzo [a,e] cyclooctene (VI) and [16] annulene (VII), as a consequence of raising the symmetry from C2h to D2h and D4h, respectively.
    Additional Material: 4 Ill.
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  • 4
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 1H- and 13C-chemical shifts of the dianion of dibenzo[a,c]naphthacene (1) have unambiguously been assigned by 2D-NMR spectroscopy. They indicate a remarkable charge distribution, as most of the negative charge is localized on the ‘anthracenic’ moiety, while the ‘phenanthrenic’ moiety is almost neutral. Association of 12- with alkali-metal counterions has only a minor effect on the chemical shifts. The charge partitioning in 12-, which is reproduced by ωβ calculations in the frame of the Hückel model, must, thus, be considered as an intrinsic property of the 4nπ-electron system of 12-. It is rationalized in terms of differing energy contents of the constituent anthracenic and phenanthrenic moieties. ESR and ENDOR studies of the radical anion 1\documentclass{article}\pagestyle{empty}\begin{document}$ 1^{\scriptstyle {{\relbar}\kern-4pt {.} }} $\end{document} and the radical cation 1\documentclass{article}\pagestyle{empty}\begin{document}$ 1^{+ \atop \dot{}} $\end{document} show that the π-charge distribution in 12- is reflected by the π-spin distributions in the two radical ions of the alternant hydrocarbon 1.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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