Carbocation

The tert-butyl cation is a relatively stable carbenium ion.[1]

A carbocation is an ion with a positively charged carbon atom. Among the simplest examples are the methenium CH+
3, methanium CH+
5, acylium ions RCO+, and vinyl C
2H+
3 cations.[2]

Until the early 1970s, carbocations were called carbonium ions.[3] 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.[4] 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.[5]

  1. ^ Scholz, Franziska; Himmel, Daniel; Scherer, Harald; Krossing, Ingo (2013). "Superacidic or Not…︁? Synthesis, Characterisation, and Acidity of the Room-Temperature Ionic Liquid [C(CH3)3]+ [Al2Br7]−". Chemistry – A European Journal. 19 (1): 109–116. doi:10.1002/chem.201203260. PMID 23180742.
  2. ^ Smith, Michael B.; March, Jerry (2007), Advanced Organic Chemistry: Reactions, Mechanisms, and Structure (6th ed.), New York: Wiley-Interscience, p. 235, ISBN 978-0-471-72091-1
  3. ^ 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.
  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.
  5. ^ 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.