Electron-accepting species

The substrate, as we can see in this example, serves in a fermentation as both the electron donating and electron accepting species. 

RedOx electrode potentials are the result of an exchange of electrons between metal and electrolyte. In Section 5.4 we have shown that the metal/metal-ion electrode potentials are the result of an exchange of metal ions between metal and electrolyte. In the RedOx system the electrode must be made of an inert metal, usually platinum, for which there is no exchange of metal ions between metal and electrolyte. The electrode acts as a source or sink for electrons. The electrolyte in the RedOx system contains two substances electron donors (electron-donating species) and electron acceptors (electron-accepting species). One example of a RedOx system is shown in Figure 5.4. In this case the electron donor is Fe ", the electron acceptor is Fe , the electrode is Pt, and the electrode process is... 

In this reaction, A is an electron-accepting species, which varies with the type of photosynthetic organism, and water serves as the electron donor in an oxidation-reduction sequence (see Fig. 19-XX) that is fundamental to all life. 

Another important coupling reaction uses esters as the electron-accepting species and leads to a-hydroxy ketones (acyloin coupling). Sodium, potassium (less frequently) or sodium-potassium alloys are commonly used as electron donors in nonpolar solvents such as toluene or xylene. The first detectable reaction intermediate after the primary reductive step is the enediolate which can be trapped with tri-alkylsilyl chloride. This method is widely used to synthesize highly nucleophilic alkenes and/or protected acyloins (Scheme 12) [50, 51]. 

Complexes as Compounds Resulting from the Interaction of Electron-Donating and Electron-Accepting Species... 

Poly acetylene, the simplest among the linear ir-conjugated polymers, is a semiconductor the conductivity is dependent on the crystallinity [1], the oxygen content [2,3], and the cis-trans content [4]. The electrical conductivity of crystalline films of poly acetylene varies from 10 S cm for the cw-isomer to 10 S cm for the ra/75-isomer [4]. Either cis- or trans-polyacetylene films can be doped with various electron-accepting species, such as halogens (L or Br.), metal halides (AsE, or FeCl,), protonic acids... 

Friedel-Crafts (Lewis) acids have been shown to be much more effective in the initiation of cationic polymerization when in the presence of a cocatalyst such as water, alkyl haUdes, and protic acids. Virtually all feedstocks used in the synthesis of hydrocarbon resins contain at least traces of water, which serves as a cocatalyst. The accepted mechanism for the activation of boron trifluoride in the presence of water is shown in equation 1 (10). Other Lewis acids are activated by similar mechanisms. In a more general sense, water may be replaced by any appropriate electron-donating species (eg, ether, alcohol, alkyl haUde) to generate a cationic intermediate and a Lewis acid complex counterion. 

A majority of chemical reactions are liable to take place at the position and in the direction where the overlapping of HO and LU of the respective reactants is maximum in an electron-donating species, HO predominates in the overlapping interaction, whereas LU does so in an electron-accepting reactant in the reacting species which have SO MO s, these play the part of HO or LU, or both"... 

Contact with a mineral surface can in many cases allow a redox reaction to proceed at a rate considerably greater than attainable within an aqueous solution itself. The catalyzing mineral sorbs the electron donating and accepting species, then, within its structure or along its surface, conducts electrons from one to the other. Where electron transfer by this pathway proceeds more rapidly than via a direct transfer in solution between colliding molecules, the redox reaction proceeds preferentially by heterogeneous catalysis. 

The reactions of halogens and hydrogen halides with alkenes are electrophilic addition reactions. This means that the initial attack on the organic molecule is by an electron-deficient species that accepts a lone pair of electrons to form a covalent bond. This species is called an electrophile. In the case of the reaction with hydrogen bromide, the mechanism for the reaction is as shown. 

Nelsen et al. (2007) have revealed one more aspect of solvent control over charge localization. Solvents with marked electron-donor properties contribute to charge localization in cation-radicals, whereas anion-radicals experience the same changes in better electron-accepting solvents. Thus, naked (non-ion-paired) anion-radicals of 4,4 -dinitrostilbene and 4,4 -dinitrotolane show the spectra of delocalized species in HMPA and THF, but essentially spectra of localized species in DMF, DMSO, and MeCN. 

Electronic excitation of molecules lead to a drastic change of their reactivities. One effect of the excitation is the powerfiil change of the redox properties, a phenomenon which may lead to photoinduced electron transfer (PET) [1-4] The electron-donating as well as the electron-accepting behavior of the excited species are approximately enhanced by excitation energy. This can be explained by means of a simple orbital scheme. By excitation of either the electron donor (D) or the acceptor (A) of a given pair of molecules, the former thermodynamically unfavorable electron transfer process becomes exergonic (A et) (Scheme 1). 

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