The anchimeric assistance of some substituents bearing the carbonyl group alters the nature of the potential-determining reaction of the cation radicals of alkylarylselenides,-instead of a charge-controlled fragmentation of the first order characteristic for these kinds of particles, the orbital-controlled second order disproportionation of dimerization take place. © 1995

Ivkov V.

Jouikov V.

Electrochimica Acta

Kazan Federal University Digital Repository

-. ’ Pergamon Elecrrochtmico Acto. Vol. 40. No. I I, pp. 1617-1622. 1995 Copyright Q 1995 Elscvier Science Ltd. Printed in Great Bntain. All rights reserved 0013-4686/95 $9.50 + 0.00 FIELD-EFFECT IN ELECTROCHEMICAL REACTIVITY OF ALKYLARYLSELENIDES V. JOUIKOV*~ and V. IVKOV$ t Laboratoire de Chimie Organique et Organomktallique, Universitt Bordeaux I, 351, tours de la Lib&ration, 33405 Talence, France 1‘ Physical Chemistry Department, Kazan State University, 420008 Kazan, Russia (Received 14 Nowmber 1994; in reckedform 24 January 1995) Abstract-The anchimeric assistance of some substituents bearing the carbonyl group alters the nature of the potential-determining reaction of the cation radicals of alkylarylselenides,-instead of a charge- controlled fragmentation of the first order characteristic for these kinds of particles, the orbital-controlled second order disproportionation of dimerization take place. Key words: electrooxidation. reactivity. field-effect, cation radicals, alkylarylselenides INTRODUCTION The electrochemical reactivity of the majority of organic selenides studied up until today in electro- oxidation processes is determined by the HOMO formed by the n-electrons of an aromatic ring and by the unshared electron pair of the selenium[lL7]. When two aromatic rings are linked with Se, the cation radicals (CRs) of such compounds show the second order potential-determining reaction[%l 11; for CRs of selenides carrying only one aromatic ring, first order reactions[6, 12-141, if not a dissociative process are observed, especially for dialkylselenides. In terms of donor-acceptor (inductive and meso- merit effects) and steric effects of substituents at the different positions of the PhSe moiety the reactivity of alkylarylselenides is unequivocally described by multiparameter correlations of E,, with CT+, (r*, -E, and R, type constants[6, 93, but from these models it is not clear whether the fragmentation of CRs of alkylarylselenides is the only reaction inherent to them. Meanwhile to be able to comprehend the path- ways of bulk reactions leading to the final products one has to know the identity of the primary reac- tions of the CRs primarily formed. In order to reveal the factors governing the nature of the potential-determining step of the oxidation of alkylarylselenides, we have synthesised and studied a number of compounds, which, when chosen, the fol- lowing were taken into account: (i) The charge density in CR is localised prefer- * Author to whom correspondence should be addressed. entially on the Se atom?. (ii) The alteration of the control of the potential- determining reaction (charge-controlled vs. orbital- controlled 2nd order interactions) could be achieved by lowering the hardness of the reaction centre or, in other words, by lowering the charge density localisa- tion on Se. The latter can be effected by introducing into the alkylarylselenides molecules the appropriate substit- uents which are able to affect the reaction centre by donor I and M-effects or by the anchimeric donor assistance. EXPERIMENTAL Instrumentation Voltammetric measurements were carried out using the PU-I polarograph, which was coupled with a microcomputer BK-0010 equipped with the home- made acquisition card based on 1113-PVlA analogous-digital converter. Rotation sweep of the electrode was controlled by the FP-37 numeric counter. A Pt oxidised rde in the three electrode t This proved by dipole moments of alkylarylselenides, by ionisation potentials PI of comprising groups and by the NMR chemical shiftsr3, 4, 11, 15-171; The E,,, of oxida- tion being close for many arylselenides[S-14jl-the corre- lation of E,,, as well as hv of photoexcitation of charge-transfer complexes by electrophilic or constants[S- 7, 13, 141: and by the fact that nucleophilic reactions of electrogenerated species, even issued from Ph,Se or Ph,Se,, occur namely on this centre[8-IO. 18-201 or on aliphatic z-carbon[9, 12, 211. 1617 

Field-effect in electrochemical reactivity of alkylarylselenides

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Field-effect in electrochemical reactivity of alkylarylselenides

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