Methanium
In chemistry, methanium is a positive ion with formula CH+
5, namely a molecule with one carbon atom bonded to five hydrogen atoms and bearing a +1 electric charge. It is a superacid and one of the onium ions, indeed the simplest carbonium ion.
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 (CH
4), by analogy with the derivation of ammonium ion (NH+
4) from ammonia (NH
3).
Methanium can be visualised as a CH3+carbenium ion with a molecule of hydrogen interacting with the empty orbital in a 3-center-2-electron bond. The bonding electron pair in the H2 molecule is shared between the two hydrogen and one carbon atoms making up the 3-center-2-electron bond.
The two hydrogen atoms in the H2 molecule can continuously exchange positions with the three hydrogen atoms in the CH3+ ion (a conformation change called pseudorotation, specifically the Berry mechanism). The methanium ion is therefore considered a fluxional molecule. The energy barrier for the exchange is quite low and occurs even at very low temperatures.
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