Rearrangement involving electron-deficient

MOLECULAR REARRANGEMENTS INVOLVING ELECTRONICALLY DEFICIENT NITROGEN ATOMS... 

There are several analogies for this kind of rearrangement that involve electron-deficient carbon (Sections 8-9B and 15-5E) and oxygen (Sections 16-9E). 

It is believed that this process involves migration through a pentacoordinate protonated cyclopropane in which an alkyl group acts as a bridge in an electron-deficient carbocation structure. The cyclohexyl- methylcyclopentyl rearrangement is postulated to occur by rearrangement between two such structures. 

Another important reaction involving migration to electron-deficient nitrogen is the Beckmann rearrangement, in which oximes are converted to amides.282... 

Rearrangements may also proceed via intermediates that are essentially cations, anions, or radicals, though those involving carbocations, or other electron-deficient species, are by far the most common. They may involve a major rearrangement of the carbon skeleton of a compound, as during the conversion of 2,3-dimethylbutan-2,3-diol (pinacol, 42) into 2,2-dimethylbutan-3-one (pinacolone, 43, cf. p. 113) ... 

The most common examples of rearrangements involve an electron-deficient atom, and pre-eminent amongst these are carbocations. Since carbocations are a feature of the SnI and El mechanisms, it follows that rearrangements can be side-reactions of these types of transformation. The driving force in carbocation rearrangements is to form a more stable carbocation. 

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