In
chemistry, methanium is a complex
positive ion with formula []
+, namely a molecule with one carbon atom covalent bond, bonded to three hydrogen atoms and one hydrogen molecule, bearing a +1 electric charge. It is a superacid and one of the
onium ion
In chemistry, an onium ion is a cation formally obtained by the protonation of mononuclear parent hydride of a pnictogen (group 15 of the periodic table), chalcogen (group 16), or halogen (group 17). The oldest-known onium ion, and the namesake ...
s, indeed the simplest
carbonium ion.
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
Victor Lvovich Talrose (russian: Виктор Львович Тальрозе, April 15, 1922 – June 22, 2004) was a Russian scientist and mass spectrometrist. He was known as the “Father of Russian Mass Spectrometry” and was the author of 44 ...
and his assistant Anna Konstantinovna Lyubimova.
methane
Methane ( , ) is a chemical compound with the chemical formula (one carbon atom bonded to four hydrogen atoms). It is a group-14 hydride, the simplest alkane, and the main constituent of natural gas. The relative abundance of methane on Ea ...
(), by analogy with the derivation of ammonium ion () from ammonia
Ammonia is an inorganic compound of nitrogen and hydrogen with the formula . A stable binary hydride, and the simplest pnictogen hydride, ammonia is a colourless gas with a distinct pungent smell. Biologically, it is a common nitrogenous wa ...
().
Structure
Fluxional methanium can be visualised as a carbenium ion with a molecule of hydrogen interacting with the empty orbital in a 3-center-2-electron bond
A three-center two-electron (3c–2e) bond is an electron-deficient chemical bond where three atoms share two electrons. The combination of three atomic orbitals form three molecular orbitals: one bonding, one ''non''-bonding, and one ''anti''-b ...
. 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 ion (a conformation change called ]pseudorotation
In chemistry, a pseudorotation is a set of intramolecular movements of attached groups (i.e., ligands) on a highly symmetric molecule, leading to a molecule indistinguishable from the initial one. The International Union of Pure and Applied Chem ...
, specifically the Berry mechanism
The Berry mechanism, or Berry pseudorotation mechanism, is a type of vibration causing molecules of certain geometries to isomerize by exchanging the two axial ligands (see Figure at right) for two of the equatorial ones. It is the most widely ac ...
). 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.[
]Infrared spectroscopy
Infrared spectroscopy (IR spectroscopy or vibrational spectroscopy) is the measurement of the interaction of infrared radiation with matter by absorption, emission, or reflection. It is used to study and identify chemical substances or function ...
has been used to obtain information about the different conformations of the methanium ion.[ The IR spectrum of plain methane has two C-H bands from symmetric and asymmetric stretching at around 3000 cm−1 and two bands around 1400 cm−1 from symmetrical and asymmetric bending vibrations. In the spectrum of three asymmetric stretching vibrations are present around 2800–3000 cm−1, a rocking vibration at 1300 cm−1, and a bending vibration at 1100 1300 cm−1.
]
Preparation
Methanium can be prepared from methane by the action of very strong acids, such as fluoroantimonic acid ( antimony pentafluoride in hydrogen fluoride HF).[
At about 270 Pa of pressure and ambient temperature, the methane ion will react with neutral methane to yield methanium and a ]methyl radical
Methyl (also systematically named trihydridocarbon) is an organic compound with the chemical formula (also written as •). It is a metastable colourless gas, which is mainly produced ''in situ'' as a precursor to other hydrocarbons in the petrol ...
:[
: + → +
The methanium ion can also be made in the gas phase via the reaction of methane and an H+ ion (i.e. a proton).
CH4 + H+(g) → CH5+
]
Stability and reactions
The cations obtained by reaction of methane with + HF , including methanium, are stabilized by interactions with the HF molecules.
At low pressures (around 1 mmHg) and ambient temperatures, methanium is unreactive towards neutral methane.[
]
See also
* Methenium
In organic chemistry, methenium (also called methylium, carbenium, methyl cation, or protonated methylene) is a cation with the formula . It can be viewed as a methylene radical (:) with an added proton (), or as a methyl radical (•) with on ...
* Ammonium
* Ethanium
References
[
V. L. Talrose and A. K. Lyubimova, Dokl. Akad. Nauk SSSR 86, 909-912 (1952) (In Russian: Тальрозе, В. Л., and А. К. Любимова. "Вторичные процессы в ионном источнике масс-спектрометра." ДАН СССР 86 (1952): 909-912)
]
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[ {{cite journal , last1 = Schreiner , first1 = Peter R. , last2 = Kim , first2 = Seung-Joon , last3 = Schaefer , first3 = Henry F. , last4 = von Ragué Schleyer , first4 = Paul , year = 1993 , title = {{chem, CH, 5, +: The never‐ending story or the final word? , journal = Journal of Chemical Physics , volume = 99 , issue = 5, pages = 3716–3720 , doi = 10.1063/1.466147 ]
Carbocations
Superacids