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The IUPAC acknowledges the three divergent definitions of carbonium ion and urges care in the usage of this term. For the remainder of this article, the term carbonium ion will be used in this latter restricted sense, while non-classical carbocation will be used to refer to any carbocation with C–C and/or C–H σ-bonds delocalized by bridging.
This led to the conclusion that the formation of S-malate proceeds as E1 elimination - protonation of fumarate to create a carbocation was followed by the addition of a hydroxyl group from H 2 O. However, more recent trials have provided evidence that the mechanism actually takes place through an acid-base catalyzed elimination by means of a ...
Structure of the 2-norbornyl cation based on X-ray crystallography. All other C-C bond lengths are normal (ca. 1.5 Å). [1] In chemistry, a carbonium ion is a cation that has a pentacoordinated carbon atom. [2] They are a type of carbocation. In older literature, the name "carbonium ion" was used for what is today called carbenium.
Figure 1: Lanosterol synthase mechanism. The discrete carbocation intermediates show the non-concerted nature of the mechanism. Though some data on the mechanism has been obtained by the use of suicide inhibitors, mutagenesis studies, and homology modeling, it is still not fully understood how the enzyme catalyzes the formation of lanosterol.
The structure is described as R−C≡O + or R− + =O. It is an acyl carbocation, but the actual structure has the oxygen and carbon linked by a triple bond. Such species are common reactive intermediates, for example, in the Friedel−Crafts acylations also in many other organic reactions such as the Hayashi rearrangement.
An example of the monovalent carbocation. A pyramidal carbocation is a type of carbocation with a specific configuration. This ion exists as a third class, besides the classical and non-classical ions. In these ions, a single carbon atom hovers over a four- or five-sided polygon, in effect forming a pyramid. The four-sided pyramidal ion will ...
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.
The vinyl cation is a carbocation with the positive charge on an alkene carbon. Its empirical formula of the parent ion is C 2 H + 3.Vinyl cation are invoked as reactive intermediates in solvolysis of vinyl halides, [1] [2] as well as electrophilic addition to alkynes and allenes.