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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.
The cationic rearrangement contraction proceeds through the loss of a leaving group and the migration of an endocyclic bond to the carbocation. Pinacol type rearrangements are often used for this type of contraction. [20] Like the expansion reaction this proceeds with an electron donating group aiding in the migration.
From PSPP, squalene is formed by a series of carbocation rearrangements. [12] [13] The process begins with ionization of pyrophosphate, giving a cyclopropylcarbinyl cation. The cation rearranges by a 1,2-migration of a cyclopropane C–C bond to the carbocation, forming the bond shown in blue to give a cyclobutyl carbocation. Subsequently, a ...
In organic chemistry, a rearrangement reaction is a broad class of organic reactions where the carbon skeleton of a molecule is rearranged to give a structural isomer of the original molecule. [1] Often a substituent moves from one atom to another atom in the same molecule, hence these reactions are usually intramolecular.
Also, there are no carbocation rearrangements, as the acylium ion is stabilized by a resonance structure in which the positive charge is on the oxygen. The viability of the Friedel–Crafts acylation depends on the stability of the acyl chloride reagent. Formyl chloride, for example, is too unstable to be isolated.
This displacement can occur via a rearrangement (path A), in which one of the sigma bonds adjacent to the diazo group migrates. This migration results in an expansion of the ring. The resulting carbocation is then attacked by a molecule of water. Alternately, the diazo group can be displaced directly by a molecule of water in an S N 2 reaction ...
Anti-Markovnikov rearrangement. This product distribution can be rationalized by assuming that loss of the hydroxy group in 1 gives the tertiary carbocation A, which rearranges to the seemingly less stable secondary carbocation B. Chlorine can approach this center from two faces leading to the observed mixture of isomers.
Carbocations are not formed in this process and thus rearrangements are not observed. The reaction follows Markovnikov's rule (the hydroxy group will always be added to the more substituted carbon). The oxymercuration part of the reaction involves anti addition of OH group but the demercuration part of the reaction involves free radical ...