Electrochemical and spectroscopic properties of a series of tert-butyl-substituted para-extended quinones
作者:Jinkui Zhou、Anton Rieker
DOI:10.1039/a607113i
日期:——
Six extended para-quinones 1–6 with
sterically hindered keto groups have been characterized by UV–VIS,
1H NMR and 13C NMR spectroscopy. Their
electrochemical properties were investigated in pyridine solution using
cyclic voltammetry, differential pulse voltammetry, chronoamperometry
and controlled-potential electrolysis. All species exhibit two
successive one-electron reductions leading to the dianions
via the monoanions; the dianions can be reoxidized to
the quinones. An EE-type mechanism for 1–6 was verified by
computer simulation; the standard rate constants
(ks1 and ks2 ) of the
heterogeneous charge-transfer are in the region of
6.5–12.5 × 10-3 cm
s-1. The first reduction peak potentials show a good
linear relationship with the calculated LUMO energy levels. The radical
anions, prepared electrochemically in the first reduction step, were
persistent for several hours in the absence of air. They were also
characterized by UV–VIS, EPR and ENDOR spectroscopy revealing that
the odd electron is delocalized over the whole π-system.
1,4-Dichlorobenzene and dichloropyridines undergo S(RN)1 reactions with various nucleophiles upon electrochemical initiation. Substitution can compete with reduction only when indirect electrolyses at low current are performed. Selective formation of monosubstitution products is observed when the nucleophiles used behave as electron-donating groups when attached to the aromatic moiety, a situation which is just the opposite of what had been observed when the same reactions were initiated photochemically. This surprising difference in behavior can be rationalized in terms of different capabilities of both activation methods to generate the key monosubstitution anion radical, ArNuX(.-). Kinetic and thermodynamic data concerning the reactivity of dichloroarenes in such processes are presented and discussed.
Synthesis and Structure of a<i>p</i>-Terphenoquinone and Paramagnetic Species Derived Therefrom
作者:Peter Boldt、Detlev Bruhnke、Fabina Gerson、Markus Scholz、Peter G. Jones、Friedrich Bär
DOI:10.1002/hlca.19930760430
日期:1993.6.30
3,5,3″,5″-Tetra(tert-butyl)-p-terphenoquinone (12b) was synthesized and characterized by its spectroscopic and X-ray structural data. The ground state of 12b is singlet with a strong contribution of a biradical structure. Paramagnetic derivative of 12b, such as the semiquinone radical anion (12bτ) and its O-protonated form, the phenoxy radical (18), were studied by ESR and ENDOR spectroscopy.
Synthesis, structure and semiconductivity of a p-terphenoquinone
作者:Robert West、John A. Jorgenson、Kimberley L. Stearley、Joseph C. Calabrese
DOI:10.1039/c39910001234
日期:——
3,3′,5,5′-Tetra-tert-butyl-p-terphenoquinone 5, the first terphenoquinone, has been obtained as metallic blue–green crystals showing anisotropic semiconductivity; the crystal structure of 5 shows that the nearly-planar molecules form slipped stacks along the needle axis.