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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.
A 1,2-rearrangement 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. Skeletal isomerization is not normally encountered in the laboratory, but is the basis of large applications in oil ...
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.
For laboratory use, the N-alkylation reaction is often unselective. A variety of alternative methods have been developed, such as the Delépine reaction , which uses hexamine . The Gabriel synthesis , involving the use of an equivalent to NH 2 − , only applies to primary alkyl halides.
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.
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.
1,2-Methyl shifts also occur in vinyl cations, and like 1,2-hydride shifts, they have higher activation barriers compared to their alkyl cation equivalents. In the protonation of alkynes, both 1,2-hydride and 1,2-methyl shifts may take place. The preference depends on the alkyl substituent since it will dictate the resulting allyl cation product.