Editing Carbocation (section)

{{Short description|Ion with a positively charged carbon atom}}
[[File:Tert-butyl cation resonance (cropped).svg|thumb|120px|The ''tert''-butyl cation is a relatively stable carbenium ion.<ref>{{cite journal |doi=10.1002/chem.201203260 |title=Superacidic or Not…︁? Synthesis, Characterisation, and Acidity of the Room-Temperature Ionic Liquid &#91;C(CH<sub>3</sub>)<sub>3</sub>&#93;<sup>+</sup> &#91;Al<sub>2</sub>Br<sub>7</sub>&#93;<sup>−</sup> |date=2013 |last1=Scholz |first1=Franziska |last2=Himmel |first2=Daniel |last3=Scherer |first3=Harald |last4=Krossing |first4=Ingo |journal=Chemistry – A European Journal |volume=19 |issue=1 |pages=109–116 |pmid=23180742 }}</ref>]]

'''Carbocation''' is a general term for [[ion]]s with a positively charged [[carbon]] [[atom]]. 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 ion]]s and five in the [[carbonium ion]]s. Among the simplest carbocations are the [[methenium]] {{chem|CH|3|+}} (a carbenium ion),  [[methanium]] {{chem|CH|5|+}}  (a carbonium ion), [[acylium ions]] {{chem2|RCO+}}, and [[Vinyl cation|vinyl]] {{chem|C|2|H|3|+}} cations.<ref>{{March6th|page=235}} </ref>

Until the early 1970s, carbocations were called ''carbonium ions''.<ref>{{cite book|author=Robert B. Grossman|title=The Art of Writing Reasonable Organic Reaction Mechanisms|url=https://archive.org/details/artofwritingreas00gros|url-access=registration|date=2007-07-31|publisher=Springer Science & Business Media|isbn=978-0-387-95468-4|pages=[https://archive.org/details/artofwritingreas00gros/page/105 105]}}</ref> This nomenclature was proposed by [[George Andrew Olah|G. A. Olah]].<ref name=OlahCXVIII>{{cite journal|first= George A.|last= Olah |date=1972|title=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=Journal of the American Chemical Society|volume=94|issue=3|pages=808–820 |doi=10.1021/ja00758a020}}</ref> Carbonium ions, as originally defined by Olah, are characterized by a [[Three-center two-electron bond|three-center two-electron]] delocalized bonding scheme and are essentially synonymous with so-called '[[non-classical carbocation]]s', 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 ({{chem|CR|5|+}}, where R is H or alkyl), to the exclusion of non-classical carbocations like the [[ Norbornyl cation |2-norbornyl cation]].<ref>{{Cite journal|last1=Sommer|first1=J.|last2=Jost|first2=R.|date=2000-01-01|title=Carbenium and carbonium ions in liquid- and solid-superacid-catalyzed activation of small alkanes|journal=Pure and Applied Chemistry|language=en|volume=72|issue=12|pages=2309–2318|doi=10.1351/pac200072122309|issn=1365-3075|doi-access=free}}</ref>