Substitution by the One-Electron Transfer Mechanism

One more mechanism for substitution at C(sp )-X bonds, the one-electron transfer mechanism, should be discussed. This mechanism is related to the SrnI mechanism, but it is not a chain mechanism. Instead, after one-electron transfer from 

It is not possible to distinguish the electron transfer mechanism from the Sn2 or SRNI mechanism by cursory examination of the reaction conditions and substrates, so it is rarely appropriate to propose this mechanism. However, you should be aware that some chemists believe that all substitution reactions are initiated by electron transfer. 

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