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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 ...
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.
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.
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.
Alkylation is a chemical reaction that entails transfer of an alkyl group. The alkyl group may be transferred as an alkyl carbocation, a free radical, a carbanion, or a carbene (or their equivalents). [1] Alkylating agents are reagents for effecting alkylation. Alkyl groups can also be removed in a process known as dealkylation.
For example, methanol has been shown to promote aryl migration. [11] [12] As shown below, if the reaction of piperanol (IV) with diazomethane is carried out in the absence of methanol, the ketone obtained though a hydride shift is the major product (V). If methanol is the solvent, an aryl shift occurs to form the aldehyde (VI), which cannot be ...
There are many examples where the Wolff rearrangement is used to contract cyclopentanone to cyclobutane. [32] The rearrangement is commonly used to form strained bicyclic and ring-fused systems. There exist a handful of examples of ring contractions from cyclobutanones to cyclopropanes. [33]