Carbenium ion of methanetert-Butyl cation, demonstrating planar geometry and sp2 hybridizationCarbonium ion of methane
A carbocation is an ion with a positively charged carbon atom. Among the simplest examples are the methenium CH+ 3, methanium CH+ 5 and vinyl C 2H+ 3 cations. Occasionally, carbocations that bear more than one positively charged carbon atom are also encountered (e.g., ethylene dication C 2H2+ 4).[1]
Until the early 1970s, all carbocations were called carbonium ions.[2] In the present-day definition given by the IUPAC, a carbocation is any even-electron cation with significant partial positive charge on a carbon atom. They are further classified in two main categories according to the coordination number of the charged carbon: three in the carbenium ions and five in the carbonium ions. This nomenclature was proposed by G. A. Olah.[3] Carbonium ions, as originally defined by Olah, are characterized by a three-center two-electron delocalized bonding scheme and are essentially synonymous with so-called 'non-classical carbocations', which are carbocations that contain bridging C–C or C–H σ-bonds. However, others have more narrowly defined the term 'carbonium ion' as formally protonated or alkylated alkanes (CR+ 5, where R is H or alkyl), to the exclusion of non-classical carbocations like the 2-norbornyl cation.[4]
^Grützmacher, Hansjörg; Marchand, Christina M. (1997). "Heteroatom stabilized carbenium ions". Coord. Chem. Rev. 163: 287–344. doi:10.1016/S0010-8545(97)00043-X.
^Robert B. Grossman (2007-07-31). The Art of Writing Reasonable Organic Reaction Mechanisms. Springer Science & Business Media. pp. 105. ISBN 978-0-387-95468-4.
^Olah, George A. (1972). "Stable carbocations. CXVIII. General concept and structure of carbocations based on differentiation of trivalent (classical) carbenium ions from three-center bound penta- of tetracoordinated (nonclassical) carbonium ions. Role of carbocations in electrophilic reactions". Journal of the American Chemical Society. 94 (3): 808–820. doi:10.1021/ja00758a020.
^Sommer, J.; Jost, R. (2000-01-01). "Carbenium and carbonium ions in liquid- and solid-superacid-catalyzed activation of small alkanes". Pure and Applied Chemistry. 72 (12): 2309–2318. doi:10.1351/pac200072122309. ISSN 1365-3075.
A carbocation is an ion with a positively charged carbon atom. Among the simplest examples are the methenium CH+ 3, methanium CH+ 5 and vinyl C 2H+ 3...
isolated. Cations, often carbocations, serve as intermediates in various types of reactions to synthesize new compounds. Carbocations are formed in two major...
accurately described using steady-state kinetics. The reaction involves a carbocation intermediate and is commonly seen in reactions of secondary or tertiary...
density with the central carbocation to stabilize it. Additionally, the surrounding sp3 hybridized carbons can stabilize the carbocation through hyperconjugation...
lab at Case Western Reserve University, and has been used to stabilize carbocations and hypercoordinated carbonium ions in liquid media. Magic acid and other...
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...
Polyvinyl chloride (PVC), a particular vinyl polymer Vinyl cation, a type of carbocation Vinyl group, a broad class of organic molecules in chemistry Vinyl polymer...
stabilize the charge on the carbocation through resonance and distribution of charge. In this case, tertiary carbocation will react faster than a secondary...
(proton) attacks the double bond forming a carbocation, which then reacts with the nucleophile (bromine). The carbocation can be formed on either side of the...
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...
involved, whether a reactive intermediate involved in the reaction is a carbocation, a carbanion or a free radical, and whether the substrate is aliphatic...
stability of the carbocation, and steric effects. As brief examples, the formation of a sterically unencumbered, stabilized carbocation favors the AdE2...
stabilizing carbocation formation, the fragmentation becomes a viable reaction pathway. The reaction generates a nitrile and a carbocation, which is quickly...
reaction}) this page is limited to neighbouring group effects seen with carbocations and SN2 reactions. In this type of substitution reaction, one group of...
Ionization: the carbon-halogen bond breaks to give a carbocation intermediate. deprotonation of the carbocation. E1 typically takes place with tertiary alkyl...
limonene is formed from geranyl pyrophosphate, via cyclization of a neryl carbocation or its equivalent as shown. The final step involves loss of a proton...
charge in an organic ion is formally centred on a carbon, it is termed a carbocation (if positively charged) or carbanion (if negatively charged). Monatomic...
from Higashimura, Sawamoto and Kennedy. Typically, generating a stable carbocation for a prolonged period of time is difficult, due to the possibility for...
Nonclassical carbocations are stabilized by charge delocalization from contributions of neighbouring C−C or C−H bonds, which can form bridged intermediates...
trans-fused carbon ring systems formed by a carbocation mediated cyclization. The remaining tertiary carbocation is quenched by a molecule of water. After...
H2O ⇌ H3O+ + HSO− 4 The protonation of isobutene in the formation of a carbocation: (CH3)2C=CH2 + HBF4 ⇌ (CH3)3C+ + BF− 4 The protonation of ammonia in...
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