Electron-donor and electron-acceptor properties of carotenoids: Electrochemical study of carotenes

The methods of polarography, voltammetry at rotating solid electrodes and cyclic voltammetry with triangle and trapezoidal pulses have been employed to study the electrochemical behavior of carotenes in various solvents (in mixtures of dimethyl-formamide and acetonitrile with benzene, in dichloroethane) at different electrodes (Hg, Pt, graphite). The capacity of carotenes to accept or donate electrons reversibly was revealed. Contrary to the general scheme, electrooxidation of carotenes was shown to proceed as a one-stage two-electron reversible process in an available range of time measured (at scan rates up to 1000 V s^?1) Formation of a number of short-living intermediate particles, products of electron transfer (anion-radicals, anions, cations) was recorded. The kinetics of the reactions with the participation of these particles was studied. Normal potentials of reversible redox transitions including those in which unstable intermediates had formed were calculated. Ionization potentials and electron affinity of β-carotene and donor—acceptor activity of carotenes was revealed: carotenes possess stronger electrondonor properties than electron-acceptor. With chlorophylls the similar asymmetry has not been observed.     

Principle of optimal deformations in planar cyclic molecules and its application to the derivatives of cyclopropane

Conclusions The principle of optimal deformations establishes relations which must apply between alterations in bond lengths and valence angles in planar cyclic molecules; they can be used to describe the changes in three-membered ring geometry resulting from the introduction of substituents, or the inclusion of a cyclopropane ring, in polycyclic systems.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 1, pp. 45–49, January, 1982.     

Trimethylsilyl and diethylboron derivatives of ethyl N-nitrocarbamate

Conclusions The trimethylsilyl and diethylboron derivatives of ethyl-N-nitrocarbamate were prepared.The former compound was found to exist as an equilibrium mixture of three stereoisomers, i.e., the N- and O-derivatives together with the previously unknown imide isomer. A mechanism of the tautomeric rearrangements in the system, involving both the charged ring intramolecular and the dissociative migration of the Si(CH₃)₃ group is suggested.The latter compound appears to exist in its imide form in which the boron atom is coordinated to the carbonyl group oxygen. The pyridine complex of this derivative has the N-isomer structure.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 11, pp. 2547–2557, November, 1976.We are grateful to N. O. Cherskaya for recording the low-temperature IR spectra of (I) and to N. I. Shlykova and O. A. Luk'yanov for their help in preparing (V).