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Thermal alkyl [1,3] shifts, similar to [1,3] hydride shifts, must proceed antarafacially. Here the geometry of the transition state is prohibitive, but an alkyl group , due to the nature of its orbitals, can invert its geometry, form a new bond with the back lobe of its sp 3 orbital, and therefore proceed via a suprafacial shift.
The actual mechanism of alkyl groups moving, as in Wagner–Meerwein rearrangement, probably involves transfer of the moving alkyl group fluidly along a bond, not ionic bond-breaking and forming. In pericyclic reactions, explanation by orbital interactions give a better picture than simple discrete electron transfers. It is, nevertheless ...
A 1,2-rearrangement or 1,2-migration or 1,2-shift or Whitmore 1,2-shift [1] is an organic reaction where a substituent moves from one atom to another atom in a chemical compound. In a 1,2 shift the movement involves two adjacent atoms but moves over larger distances are possible. In the example below the substituent R moves from carbon atom C 2 ...
When a pinacol is not symmetrical, there is a choice for which hydroxyl group will leave and which alkyl shift will occur. The selectivity will be determined by the stability of the carbocations. In this case although both choices are tertiary, the phenyl groups result in significantly higher stabilization of the positive charge through resonance.
An allylic rearrangement or allylic shift is an organic chemical reaction in which reaction at a center vicinal to a double bond causes the double bond to shift to an adjacent pair of atoms: It is encountered in both nucleophilic and electrophilic substitution , although it is usually suppressed relative to non-allylic substitution.
A Wagner–Meerwein rearrangement is a class of carbocation 1,2-rearrangement reactions in which a hydrogen, alkyl or aryl group migrates from one carbon to a neighboring carbon. [ 1 ] [ 2 ] They can be described as cationic [1,2]- sigmatropic rearrangements, proceeding suprafacially and with stereochemical retention.
In organic chemistry, an alkyl group is an alkane missing one hydrogen. [1] The term alkyl is intentionally unspecific to include many possible substitutions. An acyclic alkyl has the general formula of −C n H 2n+1. A cycloalkyl group is derived from a cycloalkane by removal of a hydrogen atom from a ring and has the general formula −C n H ...
This rearrangement differs from similar isomerizations of carbohydrates, which involve the migration of hydrogen and proceed through discrete enediol intermediates.These include the Lobry–de Bruyn–van Ekenstein transformation, [2] the Heyns [3] and Amadori rearrangements, [4] and the Voight [5] and Bilik [6] reactions. α-hydroxy imines may also undergo the rearrangement, although the ...