Carbocation rearrangement

A reaction in which a carbocation changes its carbon framework, typically by a hydride or alkyl shift, to form a more stable or differently connected carbocation.

1,2-Hydride shift: A migration of hydrogen with its bonding electron pair from one carbon to an adjacent electron-deficient carbon. This common rearrangement moves the positive charge as a neighboring C–H bond migrates.
Carbocation geometry: The geometry of a typical trivalent carbocation, with a planar carbon bonded to three groups. Its empty p orbital helps explain which neighboring bonds can overlap during a shift.
Pinacol rearrangement: An acid-catalyzed conversion of a vicinal diol into a carbonyl compound through water loss and a 1,2-shift. It is a classic rearrangement in which migration follows formation of a carbocation-like intermediate.
Nonclassical carbocation: A carbocation whose bonding electrons are delocalized across more than two carbon atoms through bridged bonding. Its bridged structure can make a rearranged-looking framework a single delocalized ion rather than a shifted classical carbocation.
1,2-Alkyl shift: A migration of an alkyl group with its bonding electron pair to an adjacent electron-deficient carbon. This shift changes carbon connectivity while relocating the carbocation.
Inductive effect: The transmission of electron-density changes through sigma bonds because of electronegativity differences. Inductive effects alter the relative stability of carbocations before and after migration.
Beckmann rearrangement: The acid-promoted conversion of an oxime into an amide or lactam by migration of a group from nitrogen to carbon. Its migration is often explained through a cationic intermediate and illustrates controlled skeletal reorganization.
Neighboring group participation: Intramolecular assistance in which a nearby group interacts with a reaction center as a bond forms or breaks. Neighboring groups can stabilize intermediates or promote migration without a simple isolated carbocation shift.
Carbocation: An ion with a positively charged carbon atom that has only six valence electrons. Rearrangements begin with a carbocation and often produce another one.
Hyperconjugation: Electron delocalization through overlap between a sigma bond and an adjacent empty or partially filled orbital. It stabilizes many carbocations and can favor rearrangement toward more substituted centers.

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