methanium
{{Short description|Ion of carbon with five hydrogens}}
{{distinguish|methenium}}
{{Chembox
| Name = Methanium
| OtherNames = carbonium (discouraged due to multiple definitions){{cite book |last1=Chemistry |first1=International Union of Pure and Applied |title=IUPAC Compendium of Chemical Terminology |chapter=carbonium ion |chapter-url=http://goldbook.iupac.org/C00839.html |year=2009 |publisher=IUPAC |access-date=27 November 2018 |language=en |doi=10.1351/goldbook.C00839|isbn=978-0-9678550-9-7 }}
| IUPACName = Methanium
| SystematicName =
| Section1 = {{Chembox Identifiers
| PubChem = 21881157
| SMILES = [C+H5]
| SMILES_Comment = true methanium
| SMILES1 = [CH3+].[HH]
| SMILES1_Comment = fluxional methanium
| InChI=1S/CH5/h1H5/q+1
| InChIKey=PXOFOHGGCICFQD-UHFFFAOYSA-N
| InChI_Comment = true methanium
| InChI1=1S/CH5/c1-2/h2H,1H3/q+1
| InChIKey1=AJLDAZFHECSILY-UHFFFAOYSA-N
| InChI1_Comment = fluxional methanium
}}
| Section2 = {{Chembox Properties
| Formula = {{chem2|CH5+}}
| C=1|H=5
| ConjugateBase = Methane
}}
| Section3 = {{Chembox Structure
| MolShape = trigonal bipyramidal
}}
| ImageFile = Chemdg methonium 1pos.svg
| ImageClass = skin-invert-image
| ImageAlt = A carbon atom, bearing a formal charge of +1, single-bonded to each of five hydrogen atoms
| ImageCaption = "True" methanium, the metastable transitional state {{chem2|[CH5]+}}
| ImageFile1 = Methonium.svg
| ImageClass1 = skin-invert-image
| ImageAlt1 = A carbon atom single-bonded to each of three hydrogen atoms and engaging in a three-center two-electron bond with two additional hydrogen atoms, the group as a whole bearing a +1 charge
| ImageCaption1 = Fluxional methanium, {{chem2|[CH3(H2)]+}}
}}
In chemistry, methanium is a complex positive ion with formula {{chem2|[CH5]+|auto=1}} (metastable transitional form, a carbon atom covalently bonded to five hydrogen atoms) or {{chem2|[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.
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.{{cite journal|last1=Nikolaev|first1=Eugene|title=Victor Talrose: an appreciation|journal=Journal of Mass Spectrometry|volume=33|issue=6|year=1998|pages=499–501|issn=1076-5174|doi=10.1002/(SICI)1096-9888(199806)33:6<499::AID-JMS684>3.0.CO;2-C|bibcode=1998JMSp...33..499N|doi-access=free}} It occurs as an intermediate species in chemical reactions.
The methanium ion is named after methane ({{chem2|CH4}}), by analogy with the derivation of ammonium ion ({{chem2|NH4+}}) from ammonia ({{chem2|NH3}}).
Structure
Fluxional methanium can be visualised as a {{chem2|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 {{chem2|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 {{chem2|H2}} molecule can continuously exchange positions with the three hydrogen atoms in the {{chem2|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.
Infrared spectroscopy 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 {{chem2|CH5+}} 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 {{chem2|SbF5}} in hydrogen fluoride HF).
At about 270 Pa of pressure and ambient temperature, the methane ion {{chem2|CH4+}} will react with neutral methane to yield methanium and a methyl radical:
:{{chem2|CH4+ + CH4 → CH5+ + CH3•}}
The methanium ion can also be made in the gas phase via the reaction of methane and an {{chem2|H+}} ion (i.e. a proton).{{cn|date=November 2022}}
:{{chem2|CH4 + H+(g) → CH5+}}
Stability and reactions
Further reading
- {{cite journal |author1= D. W. Boo |author2= Z. F. Liu |author3= A. G. Suits |author4= J. S. Tse |author5= Y. T. Lee |journal= Science |volume= 269 |pages= 57–9 |year= 1995 |doi= 10.1126/science.269.5220.57 |pmid= 17787703 |title= Dynamics of Carbonium Ions Solvated by Molecular Hydrogen: CH5+(H2)n (n= 1, 2, 3) |issue= 5220 |bibcode= 1995Sci...269...57B|s2cid= 2100896 }}
- {{cite journal |last1= Kramer |first1= G. M. |title= CH5+ Stability and Mass Spectrometry |journal= Science |volume= 286 |issue= 5442 |year= 1999 |pages= 1051a–1051 |issn= 0036-8075 |doi= 10.1126/science.286.5442.1051a |doi-access= free}}
- {{cite journal |last1= Marx |first1= D. |s2cid= 94058015 |title= MOLECULAR SPECTROSCOPY:CH5+: The Cheshire Cat Smiles |journal= Science |volume= 284 |issue= 5411 |year= 1999 |pages= 59–61 |issn= 0036-8075 |doi= 10.1126/science.284.5411.59 |bibcode= 1999Sci...284...59.}} In this unusual species
- {{cite journal |author1= Xiao-Gang Wang |author2= Tucker Carrington Jr |title= Calculated rotation-bending energy levels of CH5+ and a comparison with experiment |journal= Journal of Chemical Physics |year= 2016 |volume= 144 |issue= 20 |pages= 204304 |doi= 10.1063/1.4948549 |pmid= 27250303 |bibcode= 2016JChPh.144t4304W}}
- {{cite journal |author1= H. Schmiedt |author2= Per Jensen |author3= S. Schlemmer |title= Rotation-vibration motion of extremely flexible molecules - The molecular superrotor |journal= Chemical Physics Letters |year= 2017 |volume= 672 |pages= 34–46 |doi= 10.1016/j.cplett.2017.01.045 |bibcode= 2017CPL...672...34S|doi-access= free }}
See also
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)