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The conversion of ethanol to ethylene is a fundamental example: [3] [4] CH 3 CH 2 OH → H 2 C=CH 2 + H 2 O. The reaction is accelerated by acid catalysts such as sulfuric acid and certain zeolites. These reactions often proceed via carbocation intermediates as shown for the dehydration of cyclohexanol. [5] Some alcohols are prone to dehydration.
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.
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.
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 ...
An example is the pyrolysis of a certain sulfonate ester of menthol: E1 elimination Nash 2008, antiperiplanar relationship in blue Only reaction product A results from antiperiplanar elimination. The presence of product B is an indication that an E1 mechanism is occurring. [3] It is accompanied by carbocationic rearrangement reactions; Scheme 2.
In the second step, the nucleophilic reagent (Nuc:) attaches to the carbocation and forms a covalent sigma bond. If the substrate has a chiral carbon, this mechanism can result in either inversion of the stereochemistry or retention of configuration. Usually, both occur without preference. The result is racemization.
a carbocation by heterolysis in a nucleophilic rearrangement or anionotropic rearrangement; a carbanion in an electrophilic rearrangement or cationotropic rearrangement; a free radical by homolysis; a nitrene. The driving force for the actual migration of a substituent in step two of the rearrangement is the formation of a more stable intermediate.
The benzilic acid rearrangement is formally the 1,2-rearrangement of 1,2-diketones to form α-hydroxy–carboxylic acids using a base. This reaction receives its name from the reaction of benzil with potassium hydroxide to form benzilic acid. First performed by Justus von Liebig in 1838, [1] it is the first reported example of a rearrangement ...