Carbocations, stability migratory aptitudes

From these studies, it can be concluded that it is not a simple matter to define the general substituent migratory aptitudes in chloiin and bacteriochlorin systems, because distant conjugated peripheral substituents can dramatically affect the stability of carbocation intermediates and hence the products. The facility of the rearrangement of various substituents depends not only on the intrinsic nature of the migratory group but also on the electronic and steric factors present elsewhere on the tetrapyrrolic systems. 

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