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Electron-Exchange Reactions of Aromatic Molecules; Echanges d'Electrons de Molecules Aromatiques; Reaktsii ehlektronnogo obmena aromaticheskikh molekul; Reacciones de Intercambio Electronico en Moleculas Aromaticas

Conference:

Abstract

A large body of information is available on the rates and mechanisms of inorganic electron-exchange processes. In contrast, purely organic systems have received only minor attention. The homogeneous electron-exchange rates (k{sub exc}) and the heterogeneous rate constants for the electrode reaction (k{sub el}) have been measured only for a few hydrocarbons. We have measured k{sub exc} for a variety of aromatic systems including hydrocarbons, quinones and nitro compounds. These measurements have been carried out via electron paramagnetic resonance (EPR) line broadening measurements on mixtures of radical ions and their parent compounds. We have been able to measure k{sub exc} with a precision that allows detection of small differences presumably due to molecular structure and environment. Hydrocarbon systems like anthracene/anthracene anion are very rapid with k{sub exc} values of ca. 10{sup 8}-10{sup 9} litres mole{sup -1} sec{sup -1}. Some substituted aromatics like quinones and nitriles are also quite rapid. However, when a strong electron acceptor function is present like a nitro group in nitrobenzene, the value of k{sub exc} decreases by a factor of 10. It is possible to correlate changes in k{sub exc} in the nitrobenzene series with the unpaired electron density in terms of the {sup 14}N coupling constants  More>>
Authors:
Malachesky, P. A.; Miller, T. A.; Layloff, T.; Adams, R. N. [1] 
  1. University of Kansas, Lawrence, KS (United States)
Publication Date:
Oct 15, 1965
Product Type:
Conference
Report Number:
IAEA-SM-64/21
Resource Relation:
Conference: Symposium on Exchange Reactions, Upton, NY (United States), 31 May - 4 Jun 1965; Other Information: 30 refs., 4 tabs., 2 figs.; Related Information: In: Exchange Reactions. Proceedings of the Symposium on Exchange Reactions| 430 p.
Subject:
37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; ANIONS; ANTHRACENE; ELECTROCHEMISTRY; ELECTRODES; ELECTRON DENSITY; ELECTRON EXCHANGE; ELECTRON SPIN RESONANCE; LINE BROADENING; MOLECULAR STRUCTURE; NITROBENZENE; NITROGEN 14; QUINONES; REACTION KINETICS; SOLVATION; STEADY-STATE CONDITIONS
OSTI ID:
22117361
Research Organizations:
International Atomic Energy Agency, Vienna (Austria)
Country of Origin:
IAEA
Language:
English
Other Identifying Numbers:
Other: ISSN 0074-1884; TRN: XA13M2445073982
Submitting Site:
INIS
Size:
page(s) 157-170
Announcement Date:
Aug 01, 2013

Conference:

Citation Formats

Malachesky, P. A., Miller, T. A., Layloff, T., and Adams, R. N. Electron-Exchange Reactions of Aromatic Molecules; Echanges d'Electrons de Molecules Aromatiques; Reaktsii ehlektronnogo obmena aromaticheskikh molekul; Reacciones de Intercambio Electronico en Moleculas Aromaticas. IAEA: N. p., 1965. Web.
Malachesky, P. A., Miller, T. A., Layloff, T., & Adams, R. N. Electron-Exchange Reactions of Aromatic Molecules; Echanges d'Electrons de Molecules Aromatiques; Reaktsii ehlektronnogo obmena aromaticheskikh molekul; Reacciones de Intercambio Electronico en Moleculas Aromaticas. IAEA.
Malachesky, P. A., Miller, T. A., Layloff, T., and Adams, R. N. 1965. "Electron-Exchange Reactions of Aromatic Molecules; Echanges d'Electrons de Molecules Aromatiques; Reaktsii ehlektronnogo obmena aromaticheskikh molekul; Reacciones de Intercambio Electronico en Moleculas Aromaticas." IAEA.
@misc{etde_22117361,
title = {Electron-Exchange Reactions of Aromatic Molecules; Echanges d'Electrons de Molecules Aromatiques; Reaktsii ehlektronnogo obmena aromaticheskikh molekul; Reacciones de Intercambio Electronico en Moleculas Aromaticas}
author = {Malachesky, P. A., Miller, T. A., Layloff, T., and Adams, R. N.}
abstractNote = {A large body of information is available on the rates and mechanisms of inorganic electron-exchange processes. In contrast, purely organic systems have received only minor attention. The homogeneous electron-exchange rates (k{sub exc}) and the heterogeneous rate constants for the electrode reaction (k{sub el}) have been measured only for a few hydrocarbons. We have measured k{sub exc} for a variety of aromatic systems including hydrocarbons, quinones and nitro compounds. These measurements have been carried out via electron paramagnetic resonance (EPR) line broadening measurements on mixtures of radical ions and their parent compounds. We have been able to measure k{sub exc} with a precision that allows detection of small differences presumably due to molecular structure and environment. Hydrocarbon systems like anthracene/anthracene anion are very rapid with k{sub exc} values of ca. 10{sup 8}-10{sup 9} litres mole{sup -1} sec{sup -1}. Some substituted aromatics like quinones and nitriles are also quite rapid. However, when a strong electron acceptor function is present like a nitro group in nitrobenzene, the value of k{sub exc} decreases by a factor of 10. It is possible to correlate changes in k{sub exc} in the nitrobenzene series with the unpaired electron density in terms of the {sup 14}N coupling constants of the EPR spectra. Further, the nitro aromatic series show very large variations in k{sub exc} with the solvent system. These changes can be correlated with recent studies of the solvation effect on hyperfine coupling constants. Marcus has reviewed recently chemical and electrochemical electron-transfer theory and suggested correlations between k{sub exc} and k{sub el}. We have measured k{sub el} especially for the nitrobenzene system under conditions which are as nearly identical experimentally to the EPR studies as possible. The electrochemical investigations were carried out by a steady-state d.c. method to eliminate some of the uncertainties inherent in electrochemical relaxation techniques. Rotated disc electrodes at low temperatures were used. The solvent effects on k{sub el} (for nitrobenzene) are identical with those observed for k{sub exc}. There are, however, serious discrepancies between the values of k{sub el} observed and predicted by Marcus's theory. Some possible explanations of these discrepancies will be discussed. (author) [French] On dispose d'une importante documentation sur les vitesses et les mecanismes des processus d'echange d'electrons dans les systemes inorganiques. En revanche, les systemes purement organiques ont recu jusqu'ici une attention moindre. Les vitesses d'echange homogene d'electrons (k{sub exc}) et les constantes de vitesses d'echange heterogene (k{sub el}) pour la reaction a l'electrode n'ont ete mesurees que pour quelques hydrocarbures. Les auteurs ont mesure k{sub exc} pour divers systemes aromatiques, notamment des hydrocarbures, des quinones et des nitrocomposes. Pour cela, ils ont mesure l'elargissement desraies par resonance paramagnetique des electrons (RPE) sur des melanges de radicaux ioniques et des composes ascendants. Ils ont pu mesurer k{sub exc} avec une precision tellequ'ellepermet de deceler de petites differences, lesquelles sont sans doute dues a la structure moleculaire et au milieu. Pour les systemes d'hydrocarbures, comme le systeme anthracene/anion anthracene, la vitesse est tres elevee: les valeurs de k{sub exc} sont d'environ 10{sup 8} a 10{sup 9} l * mole{sup -1} * s{sup -1}. Les vitesses sont egalement elevees pour certains composes aromatiques substitues comme les quinones et les nitriles. Toutefois, lorsqu'un accepteur d'electrons fort est present, comme par exemple un groupe nitro dans le nitrobenzene, la valeur de k{sub exc} diminue d'un facteur de 10. On peut trouver une correlation entre les variations de k{sub exc} dans la serie du nitrobenzene avec la densite des electrons celibataires, selon les constantes de couplage de {sup 14}N du spectre de RPE. La serie nitro-aromatique accuse en outre de tres fortes variations de k{sub exc} selon le systeme solvant. On peut rapprocher ces variations des recentes etudes de l'effet de solvatation sur les constantes de couplage hyperfines. Marcus a examine recemment la theorie du transfert chimique et electrochimique d'electrons et a suggere des correlations entre k{sub exc} et k{sub el}. Les auteurs ont mesure k{sub el} notamment pour le nitrobenzene dans des conditions experimentales qui sont aussi proches que possible des etudes par RPE. Pour les recherches electrochimiques, onaapplique une methode a courant continu enregimestationnaire, de maniere a eliminer certaines des incertitudes inherentes aux techniques de relaxation electrochimique. On a utilise des electrodes a disques tournants a basse temperature. Les effets du solvant sur k{sub el} (pour le nitrobenzene) sont identiques a ceux qui ont ete observes pour k{sub exc}- Mais o n releve des ecarts considerables entre les valeurs de k{sub el} observees et celles qui ont ete calculees par la theorie de Marcus, les auteurs discutent plusieurs explications possibles de ces ecarts. (author) [Spanish] Se posee abundante informacion sobre las velocidades y mecanismos de los procesos de intercambio electronico en sustancias inorganicas. En cambio, se ha prestado menor atencion a los sistemas puramente organicos. Las velocidades de intercambio homogeneo de electrones (k{sub exc}) y las constantes de velocidad de intercambio heterogeneo en los electrodos (k{sub el}) solo se han medido en el caso de contados hidrocarburos. Los autores han determinado el valor de k{sub exc} en una serie de sistemas aromaticos que comprende hidrocarburos, quinonas y nitro compuestos. A tal efecto, han medido el ensanchamientode las lfneas por resonancia paramagnetica de los electrones en mezclas de radicales ionicos y de sus precursores. Los autores han podido medir el valor de k{sub exc} con una precision que permite observar ligeras variaciones debidas probablemento a la estructura molecular y al medio. En los sistemas de hidrocarburos como el antraceno/anion antraceno la velocidad de intercambio es muy elevada, siendo los valores de k{sub exc} del orden de 10{sup 8} a 10{sup 9} l mol{sup -1} s{sup -1}. Las velocidades son tambien elevadas para algunos compuestos aromaticos sustituidos, como quinonas y nitrilos. Sin embargo, en presencia de un fuerte aceptor de electrones, como el grupo nitro del nitrobenceno, el valor de k{sub exc} es 10 veces menor. Es posible correlacionar las variaciones de k{sub exc} e n la serie del nitrobenceno con la densidad de electrones no apareados en funcion de las constantes de acoplamiento del {sup 14}N en los espectros de resonancia paramagnetica de los electrones. Asimismo, las series nitroaromaticas presentan considerables variaciones de k{sub exc} segun el solvente empleado. Estas variaciones pueden vincularse con los resultados de recientes estudios del efecto de solvatacion sobre las constantes de acoplamiento hiperfinas. Marcus ha estudiado recientemente la, teoria de la transferencia quumca y electroquimica de electrones y propuesto correlaciones entre k{sub exc} y k{sub el}. Los autores han medido k{sub el}, especialmente en el nitrobenceno, en condiciones experimentales lo mas analogas posibles a las de los estudios por resonancia paramagnetica de los electrones. Las investigaciones electroquimicas se efectuaron con corriente continua estabilizada para eliminar, algunas de las indeterminaciones inherentes a las tecnicas de relajacion electroquimica. Se utilizaron como electrodos discos giratorios a baja temperatura. Los efectos del solvente en el valor de k{sub el} (en el caso nitrobenceno) son identicos a los observados respecto de k{sub exc}. No obstante, existen considerables discrepancias entre los valores de k{sub el} observados y los previstos segun la teoria de Marcus. Se examinan algunas explicaciones plausibles de estas discrepancias. (author) [Russian] Imeetsja bol'shoe kolichestvo informacii otnositel'no skorosti mehanizma processov neorganicheskogo obmena jelektronov. V protivopolozhnost' jetomu chisto organicheskim sistemam udeljalos' dovol'no neznachitel'noe vnimanie. Skorost' gomogennogo jelektronnogo obmena (k{sub 0bm})i geterogennye konstanty skorosti dlja jelektrodnoj reakcii (k{sub jel}) byli izmereny lish' dlja neskol'kih ugle- vodorodov . Bylo izmereno k{sub 0bm} dlja razlichnyh aromaticheskih sistem, v tom chisle uglevodorodov, hinonov i nitrosoedinenij. Jeti izmerenija byli provedeny posredstvom jelektronnogo para- magnitnogo rezonansa (EPR) s perenosom izmerenij na smesi radikal'nyh ionov i ih mate- rinskih soedinenij. Nam takzhe udalos' izmerit' k0bm s takoj tochnost'ju, kotoraja pozvo- ljaet obnaruzhit' nebol'shie razlichija, vyzvannye, verojatno; molekuljarnoj strukturoj i sre- doj. Uglevodorodnye sistemy, podobnye antracenovomu/antracenovomu anionu, javljajutsja ves'ma bystrymi pri velichine k{sub 0gM} priblizitel'no 10{sup 8}-10{sup 9} litr mol{sup -i} sek{sup -1}. Nekotorye zame- shhennye aromaticheskie soedinenija, podobnye hinonam i nitrilam, takzhe javljajutsja ves'ma bystrymi. Odnako, kogda imeetsja sil'naja funkcija jelektronnogo akceptora, podobno nitro- gruppe v nitrobenzole, velichina k{sub 0gM} sokrashhaetsja na faktor 10. Predstavljaetsja vozmozhnym korrelirovat' izmenenija v k{sub obm} v serijah nitrobenzola s pomoshh'ju plotnosti neparnyh jelek- tronov po konstantam svjazi N{sup 14} spektra EPR. Krome togo, nitroaromaticheskie serii obna- ruzhivajut ochen' bol'shie razlichija v znachenijah k{sub 0b} m s rastvorjajushhej sistemoj. Jeti izmene- nija mozhno korrelirovat' blagodarja nedavnim issledovanijam jeffekta sol'vatacii na sverh- tonkie konstanty svjazi. V poslednee vremja Markus rassmotrel teoriju himicheskogo i jelektrohimicheskogo pere- nosa jelektronov i predlozhil korreljacii mezhdu znachenijami k{sub obm} i k{sub jel}. Nami special'no byl izmeren kjel dlja sistemy nitrobenzola v uslovijah, kotorye jeksperimental'no byli - pochti identichny uslovijam pri izuchenii EPR. Elektrohimicheskie issledovanija provodilis' metodom tverdogo sostojanija de s tem, chtoby iskljuchit' nekotorye neopredelennosti, pri- sushhie metodam jelektrohimicheskoj relaksacii. Ispol'zovalis' pri nizkih temperaturah vrashhajushhiesja diskovye jelektrody. Rastvorjajushhie jeffekty po k{sub je} l (dlja nitrobenzola) iden- tichny jeffektam, nabljudavshimsja dlja k{sub 0bm} - Odnako imejutsja ser'eznye rashozhdenija mezhdu velichinami nabljudavshegosja k{sub Jel} i predskazannymi teoriej Markusa. Dajutsja nekotorye vozmozhnye raz'jasnenija jetih rashozhdenij. (author)}
place = {IAEA}
year = {1965}
month = {Oct}
}