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  • General Chemistry  (2)
  • Theoretical, Physical and Computational Chemistry  (1)
  • nucleophilic addition  (1)
  • 1
    Electronic Resource
    Electronic Resource
    Nucleophilic addition versus electron transfer in carbonylmetallate salts. Donor-acceptor interactions in the precursor ion pairsDedicated to Fred Bordwell for his seminal contributions to our understanding of nucleophilic reactivity (1997)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 10 (1997), S. 542-562 
    Details
    ISSN: 0894-3230
    Keywords: nucleophilic addition ; electron transfer ; carbonylmetallate salts ; donor-acceptor interactions ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: ---The isostructural pentacarbonylmetallate anions M(CO)-5 (M=Mn and Re) react with a series of N-methylpyridinium cations (Py+) to yield products of nucleophilic addition [NA=Py-M(CO)5] or of one-electron redox reaction [ET=Py·+M(CO)·5]. The partitioning of the reaction along the two reaction pathways is controlled by steric factors and the electronic structure of the pyridinium cation, with cations which form stable, delocalized radicals favoring the ET pathway. The central metal also plays a role in determining the stoichiometry, and the NA pathway is favored by the rhenate anion and ET by the manganate analogue. Rates of both reactions correlate with the driving force for electron transfer, and the differing reaction pathways are not distinguished on the basis of linear free energy relations, previously discussed by Bordwell and co-workers. The contact ion pair [Py+, M(CO)-5] is identified as the critical precursor for both electron transfer and nucleophilic coupling. Based on these observations, it is proposed that the rates and mechanisms of these interionic reactions are controlled by donor-acceptor bonding in the transition states, which in turn is directly related to the charge-transfer interactions extant in the ion-pair intermediate. © 1997 John Wiley & Sons, Ltd.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
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    Paper (German National Licenses)
  • 2
    Electronic Resource
    Electronic Resource
    Elektronen- und Ladungsübertragung: Zur Vereinheitlichung der Mechanismen organischer und metallorganischer Reaktionen (1988)
    Weinheim : Wiley-Blackwell
    Zeitschrift für die chemische Industrie 100 (1988), S. 1331-1372 
    Details
    ISSN: 0044-8249
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Die große Vielfalt organischer und metallorganischer Reaktionen kann bei Betrachtung aller Nucleophile und Elektrophile als Elektronendonoren (D) bzw. -acceptoren (A) mit einem vereinheitlichenden Mechanismus beschrieben werden. Der Vergleich von „outer-sphere“- und „inner-sphere“-Elektronenübertragungen mit Hilfe der Marcus-Theorie liefert die thermochemische Basis der „Verallgemeinerten Freien-Enthalpie-Beziehung für die Elektronenübertragung“ (generalized Free Energy Relationship for Electron Transfer, FE-RET) - siehe Gleichung (37) sowie die daraus folgenden Gleichungen (43) und (44) -, die auf elektrophile aromatische Substitutionen, Additionen an Olefine, Spaltungen von Alkyl-metallverbindungen etc. breit anwendbar ist. FERET basiert auf der Umwandlung der durch schwache Nucleophil-Elektrophil-Wechselwirkungen gekennzeichneten, allgegenwärtigen Elektronen-Donor-Acceptor(EDA)-Vorläuferkomplexe [D, A] in Radikalionen-paare [D⊕, A-], wofür die Änderung der Freien Enthalpie nach der Mulliken-Theorie aus den Charge-Transfer-Absorptionsspektren abgeschätzt werden kann. Die FERET-Analyse läßt darauf schließen, daß die Charge-Transfer-Ionenpaare [D⊕, A⊖] den Übergangszuständen von Nucleophil/Elektrophil-Umwandlungen energetisch äquivalent sind. Das Verhalten solcher Ionenpaare kann in einigen Fällen unmittelbar nach einem 25ps-Laserpuls auf die Charge-Transfer-Bande des EDA-Vorläuferkomplexes direkt beobachtet werden. Derartige Studien bestätigen beispielsweise das Radikalpaar [Aren⊙⊕, NO2⊖] als existenzfähiges Intermediat der elektrophilen Nitrierung von Arenen, wie anhand des Mechanismus der Elektronenübertragung von Arenen auf das Nitryl-Kation NO2⊕ als Elektrophil beschrieben wird.
    Additional Material: 38 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/ange.19881001008
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  • 3
    Electronic Resource
    Electronic Resource
    Electron Transfer and Charge Transfer: Twin Themes in Unifying the Mechanisms of Organic and Organometallic Reactions (1988)
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 27 (1988), S. 1227-1266 
    Details
    ISSN: 0570-0833
    Keywords: Electron transfer ; Charge transfer ; Reaction mechanisms ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The broad varieties of organic and organometallic reactions merge into a common unifying mechanism by considering all nucleophiles and electrophiles as electron donors (D) and electron acceptors (A), respectively. Comparison of outer-sphere and inner-sphere electron transfers with the aid of Marcus theory provides the thermochemical basis for the generalized free energy relationship for electron transfer (FERET) in Equation (37) and its corollaries in Equations (43) and (44) that have wide predictive applicability to electrophilic aromatic substitutions, olefin additions, organometallic cleavages, etc. The FERET is based on the conversion of the weak nucleophile-electrophile interactions extant in the ubiquitous electron donor - acceptor (EDA) precursor complex [D, A] to the radical ion pair [D⊕, A⊖], for which the free energy change can be evaluated from the charge-transfer absorption spectra according to Mulliken theory. FERET analysis thus indicates that the charge-transfer ion pairs [D⊕, A⊖] are energetically equivalent to the transition states for nucleophile/electrophile transformations. The behavior of such ion pairs can be directly observed immediately following the irradiation of the charge-transfer bands of various EDA complexes with a 25-ps laser pulse. Such studies confirm the radical ion pair [Arene⊕, NO2] as a viable intermediate in electrophilic aromatic nitration, as presented in the electron-transfer mechanism between arenes and the nitryl cation (NO2⊕) electrophile.
    Additional Material: 38 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/anie.198812273
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