Editing Carbocation (section)

===Carbonium ions===
[[File:CSD CIF HIGNAOhires.png|thumb|Structure of the 2-norbornyl non-classical carbenium ion.  All other C-C bond lengths are normal (ca. 1.5 Å).<ref name=":0">{{Cite journal|last1=Scholz|first1=F.|last2=Himmel|first2=D.|last3=Heinemann|first3=F. W.|last4=Schleyer|first4=P. v R.|last5=Meyer|first5=K.|last6=Krossing|first6=I.|date=2013-07-05|title=Crystal Structure Determination of the Nonclassical 2-Norbornyl Cation|journal=Science|language=en|volume=341|issue=6141|pages=62–64|doi=10.1126/science.1238849|issn=0036-8075|pmid=23828938|bibcode=2013Sci...341...62S|s2cid=206549219 }}</ref> ]]

Carbonium ions can be thought of as protonated or alkylated alkanes, bearing the general formula CR<sub>5</sub><sup>+</sup> (R = alkyl or H).  A typical example is the [[Methanium|methanium ion]], CH<sub>5</sub><sup>+</sup>, which is formed by protonation of methane using a [[superacid]].  By necessity of having five bonds on carbon but only four valence electron pairs available for bonding, they feature delocalized 3c-2e σ bonding and are thus regarded as type of non-classical carbocation.  Like carbenium ions, carbonium ions are often invoked as intermediates in the upgrading of hydrocarbons in refineries.  They are generally fleeting intermediates with [[Fluxional molecule|fluxional structures]] that are challenging to observe and interpret spectroscopically.  They can undergo decomposition by expulsion of a proton or alkyl group, or by loss of H<sub>2</sub> to give a carbenium ion.