Types of Electron Transfer Reactions

In addition to the type of electron transfer reaction, shown in Equations 6.142-6.145, there are examples where pure MLCT excited states induce ligand substitutions by associative or dissociative mechanisms. A well-established example of a MLCT excited state-mediated ligand labilization reaction is shown in Equation 6.149.136... 

Another example is the assembly of the complex [6-7-5]-fused tricyclic core 35 of guanacastepenes, obtained as a single diastereoisomer, as shown in Scheme 22 <2005OL3425>. The efficiency of this reaction is consistent with the gi OT-dialkyl effect that is required for the seven-membered ring formation in this type of electron-transfer reaction. 

This type of electron transfer reaction requires the presence of a donor-acceptor couple, and is triggered by light excitation on one of the two reaction partners. The species which absorbs the exciting light must possess appropriate photophysical properties such as a long-lived excited state at suitable energy. The quencher, on the other hand, must possess appropriate redox levels. 

Thus superadditivity can be viewed as a sequence of two types of electron transfer reaction, one which is heterogeneous between Metol and the latent image, resulting in silver development, and one which is homogeneous between hydroquinone and... 

The main point to stress from a biocatalytic perspective is the unique nature of the flavin cofactor in these types of electron transfer reactions. Whereas all other... 

In 1954, King and Taube published the 1980 Nobel Prize winning work that defined these two different types of electron transfer reactions. In an inner-sphere mechanism, the atoms undergoing redox form bonds to a common atom (or small group of atoms), which then serves as a bridge for electron transfer (ISPC = inner-sphere precursor complex and ket = electron transfer rate constant). 

Theory of this type of electron transfer reactions has been recently reviewed by the author in Ref. [19,44] the reader is also referred to a related Ref [45] where concerted ET/PT reactions are discussed. 

The simplest type of electron transfer reaction is the self-exchange reactimi, for example, the transfer of an electron from an FeCHaO) to an Fe(H20)6. The AG° in (114) is now zero, v/ and are equal, and ai = 02- This class of reactions (known in the literature as self exchange or isotopic exchange reactions) is the simplest class of reactions in all of chemistry. In a simple electron transfer, no chemical bonds are broken or are formed. The w in (112) and (113) is now —1/2. Apart from w and w in (114) and (116), the free energy barrier to reaction AG is A/4. 

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