Methanium

In chemistry, methanium is a complex positive ion with formula [CH5]+ (metastable transitional form, a carbon atom covalently bonded to five hydrogen atoms) or [CH3(H2)]+ (fluxional form, namely a molecule with one carbon atom covalently bonded to three hydrogen atoms and one dihydrogen molecule), bearing a +1 electric charge. It is a superacid and one of the onium ions, indeed the simplest carbonium ion.

Not to be confused with methenium.
Methanium

"True" methanium, the metastable transitional state [CH5]+

Fluxional methanium, [CH3(H2)]+
Names
IUPAC name
Methanium
Other names
carbonium (discouraged due to multiple definitions)
Identifiers
3D model (JSmol)
  • true methanium: InChI=1S/CH5/h1H5/q+1
    Key: PXOFOHGGCICFQD-UHFFFAOYSA-N
  • fluxional methanium: InChI=1S/CH5/c1-2/h2H,1H3/q+1
    Key: AJLDAZFHECSILY-UHFFFAOYSA-N
  • true methanium: [C+H5]
  • fluxional methanium: [CH3+].[HH]
Properties
CH+5
Molar mass 17.051 g·mol−1
Conjugate base Methane
Structure
trigonal bipyramidal
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references

It is highly unstable and highly reactive even upon having a complete octet, thus granting its superacidic properties.

Methanium can be produced in the laboratory as a rarefied gas or as a dilute species in superacids. It was prepared for the first time in 1950 and published in 1952 by Victor Talrose and his assistant Anna Konstantinovna Lyubimova. It occurs as an intermediate species in chemical reactions.

The methanium ion is named after methane (CH4), by analogy with the derivation of ammonium ion (NH+4) from ammonia (NH3).

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