Electron transfer adjacent atom attack

Electron transfer reactions mediated by [Co(CN)5]3 proceed via attack on the adjacent S atom with the rate of reaction (34) being considerably faster than reaction (35), both leading to the S-bonded [Co(CN)5(SCN)]3 isomer (44).213 Similarly [Co(CN)3]3 appears to react with [Hg(SeCN)4]2 via the bridged species (45, Scheme 24). 

The complexation results in partial electron transfer from the epoxide to the metal, rendering the methylene carbon atom of the ring more prone to nudeophilic attack. Coordination also induces a concerted dectron transfer between the two adjacent aluminum atoms, which weakens the polymer-aluminum bond, increasing reaaivity of the corresponding alkoxide moieties toward the elearophilic carbon of the neighboring epoxide. 

Adenosylmethionine (Ado-Met) is the most important donor of alkyl groups, which are transferred from the sulfonium pole to a variety of nucleophilic molecular species within the cell. The reaction involves nucleophilic attack to one of the three carbon atoms adjacent to the electron-deficient trivalent sulfur (see Figure 1) and is catalyzed by specific enzymes. Whereas the transfer of the methyl group occurs in a large variety of reactions 3 the transfer of both the adenosyl moiety and of the 3-amino-3-carboxypropyl group have been described in very few instances the acceptor molecules are enzyme proteins for the adenosyl moiety ", and transfer RNA (tRNA) for the 3-amino-3-carboxypropyl group . 

Figure 7-7 The alkene-forming step in unimolecular elimination (El) deprotonation of a 1,1-dimethylethyl (fert-butyl) cation by the solvent methanol. In an orbital description of proton abstraction, an eiectron pair on the oxygen atom in the solvent attacks a hydrogen on a carbon adjacent to that bearing the positive charge. The proton is transferred, leaving an electron pair behind. As the carbon rehybridizes from sp to sp, these electrons redistribute over the two p orbitals of the new double bond.

Obviously, the site of the primary attack of trifluoroacetyl cation is nitrogen atom of the azo group adjacent to the benzene ring (Scheme 2.182). In the cation I, the positive charge should be mainly concentrated on the pyrrole nitrogen due to electron density transfer from the pyrrole counterpart of the molecule to ionized azo group. One of the tentative pathways of this intermediate fragmentation is elimination of the vinyl cation with subsequent release of proton. Protonation of trifluoroacetamide... 

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