Methanium

Ion of carbon with five hydrogens

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)[1]

Identifiers

3D model (JSmol)

* true methanium: Interactive image
* fluxional methanium: Interactive image

PubChem CID

* 21881157

InChI

* 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

SMILES

* true methanium: [C+H5]

* fluxional methanium: [CH3+].[HH]

Properties

Chemical formula

| CH+5
Molar mass | 17.051 g·mol−1
Conjugate base | Methane
Structure

Molecular shape

| trigonal bipyramidal

Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).

Infobox references

Chemical compound

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.

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.[2][3] 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).

## Structure

[edit]

Fluxional methanium can be visualised as a CH+3 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.[4]

The two hydrogen atoms in the H2 molecule can continuously exchange positions with the three hydrogen atoms in the CH+3 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.[5][6]

Infrared spectroscopy has been used to obtain information about the different conformations of the methanium ion.[7][8][9] 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 CH+5 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

[edit]

Methanium can be prepared from methane by the action of very strong acids, such as fluoroantimonic acid (antimony pentafluoride SbF5 in hydrogen fluoride HF).[10]

At about 270 Pa of pressure and ambient temperature, the methane ion CH+4 will react with neutral methane to yield methanium and a methyl radical:[11]

CH+4 \+ CH4 → CH+5 \+ CH3•

The methanium ion can also be made in the gas phase via the reaction of methane and an H+ ion (i.e. a proton).[citation needed]

CH4 \+ H+(g) → CH+5

## Stability and reactions

[edit]

The cations obtained by reaction of methane with SbF5 \+ 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.[11]

## Further reading

[edit]

* D. W. Boo; Z. F. Liu; A. G. Suits; J. S. Tse; Y. T. Lee (1995). "Dynamics of Carbonium Ions Solvated by Molecular Hydrogen: CH5+(H2)n (n= 1, 2, 3)". Science. 269 (5220): 57–9\. Bibcode:1995Sci...269...57B. doi:10.1126/science.269.5220.57. PMID 17787703. S2CID 2100896.
* Kramer, G. M. (1999). "CH5+ Stability and Mass Spectrometry". Science. 286 (5442): 1051a–1051. doi:10.1126/science.286.5442.1051a. ISSN 0036-8075.
* Marx, D. (1999). "MOLECULAR SPECTROSCOPY:CH5+: The Cheshire Cat Smiles". Science. 284 (5411): 59–61\. Bibcode:1999Sci...284...59.. doi:10.1126/science.284.5411.59. ISSN 0036-8075. S2CID 94058015.
* Xiao-Gang Wang; Tucker Carrington Jr (2016). "Calculated rotation-bending energy levels of CH5+ and a comparison with experiment". Journal of Chemical Physics. 144 (20): 204304. Bibcode:2016JChPh.144t4304W. doi:10.1063/1.4948549. PMID 27250303.
* H. Schmiedt; Per Jensen; S. Schlemmer (2017). "Rotation-vibration motion of extremely flexible molecules - The molecular superrotor". Chemical Physics Letters. 672: 34–46\. Bibcode:2017CPL...672...34S. doi:10.1016/j.cplett.2017.01.045.

## See also

[edit]

* Methenium
* Ammonium
* Ethanium

## References

[edit]

1. ^ Chemistry, International Union of Pure and Applied (2009). "carbonium ion". IUPAC Compendium of Chemical Terminology. IUPAC. doi:10.1351/goldbook.C00839. ISBN 978-0-9678550-9-7. Retrieved 27 November 2018.
2. ^ 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)
3. ^ Nikolaev, Eugene (1998). "Victor Talrose: an appreciation". Journal of Mass Spectrometry. 33 (6): 499–501\. Bibcode:1998JMSp...33..499N. doi:10.1002/(SICI)1096-9888(199806)33:6<499::AID-JMS684>3.0.CO;2-C. ISSN 1076-5174.
4. ^ Rasul, Golam; Prakash, G.K. Surya; Olah, George A. (2011). "Comparative study of the hypercoordinate carbonium ions and their boron analogs: A challenge for spectroscopists". Chemical Physics Letters. 517 (1–3): 1–8\. Bibcode:2011CPL...517....1R. doi:10.1016/j.cplett.2011.10.020.1–3&rft.pages=1-8&rft.date=2011&rft_id=info:doi/10.1016/j.cplett.2011.10.020&rft_id=info:bibcode/2011CPL...517....1R&rft.aulast=Rasul&rft.aufirst=Golam&rft.au=Prakash,+G.K.+Surya&rft.au=Olah,+George+A.&rfr_id=info:sid/en.wikipedia.org:Methanium" class="Z3988">
5. ^ Schreiner, Peter R.; Kim, Seung-Joon; Schaefer, Henry F.; von Ragué Schleyer, Paul (1993). "CH+
5: The never-ending story or the final word?". Journal of Chemical Physics. 99 (5): 3716–3720\. doi:10.1063/1.466147.CH+5:+The+never-ending+story+or+the+final+word?&rft.volume=99&rft.issue=5&rft.pages=3716-3720&rft.date=1993&rft_id=info:doi/10.1063/1.466147&rft.aulast=Schreiner&rft.aufirst=Peter+R.&rft.au=Kim,+Seung-Joon&rft.au=Schaefer,+Henry+F.&rft.au=von+Ragué+Schleyer,+Paul&rfr_id=info:sid/en.wikipedia.org:Methanium" class="Z3988">
6. ^ Müller, Hendrik; Kutzelnigg, Werner; Noga, Jozef; Klopper, Wim (1997). "CH5+: The story goes on. An explicitly correlated coupled-cluster study". Journal of Chemical Physics. 106 (5): 1863. Bibcode:1997JChPh.106.1863M. doi:10.1063/1.473340.
7. ^ White, Edmund T.; Tang, Jian; Oka, Takeshi (1999). "CH+
5: The infrared spectrum observed". Science. 284 (5411): 135–7\. Bibcode:1999Sci...284..135W. doi:10.1126/science.284.5411.135. PMID 10102811.CH+5:+The+infrared+spectrum+observed&rft.volume=284&rft.issue=5411&rft.pages=135-7&rft.date=1999&rft_id=info:pmid/10102811&rft_id=info:doi/10.1126/science.284.5411.135&rft_id=info:bibcode/1999Sci...284..135W&rft.aulast=White&rft.aufirst=Edmund+T.&rft.au=Tang,+Jian&rft.au=Oka,+Takeshi&rfr_id=info:sid/en.wikipedia.org:Methanium" class="Z3988">
8. ^ Oskar Asvany, Padma Kumar P; Redlich, Britta; Hegemann, Ilka; Schlemmer, Stephan; Marx, Dominik (2005). "Understanding the infrared spectrum of bare CH+
5". Science. 309 (5738): 1219–1222\. Bibcode:2005Sci...309.1219A. doi:10.1126/science.1113729. PMID 15994376. S2CID 28745636.CH+5.&rft.volume=309&rft.issue=5738&rft.pages=1219-1222&rft.date=2005&rft_id=info:doi/10.1126/science.1113729&rft_id=https://api.semanticscholar.org/CorpusID:28745636#id-name=S2CID&rft_id=info:pmid/15994376&rft_id=info:bibcode/2005Sci...309.1219A&rft.aulast=Oskar+Asvany&rft.aufirst=Padma+Kumar+P&rft.au=Redlich,+Britta&rft.au=Hegemann,+Ilka&rft.au=Schlemmer,+Stephan&rft.au=Marx,+Dominik&rft_id=https://doi.org/10.1126%2Fscience.1113729&rfr_id=info:sid/en.wikipedia.org:Methanium" class="Z3988">
9. ^ Huang, Xinchuan; McCoy, Anne B.; Bowman, Joel M.; Johnson, Lindsay M.; Savage, Chandra; Dong, Feng; Nesbitt, David J. (2006). "Quantum deconstruction of the infrared spectrum of CH+
5". Science. 311 (5757): 60–63\. Bibcode:2006Sci...311...60H. doi:10.1126/science.1121166. PMID 16400143. S2CID 26158108.CH+5.&rft.volume=311&rft.issue=5757&rft.pages=60-63&rft.date=2006&rft_id=info:doi/10.1126/science.1121166&rft_id=https://api.semanticscholar.org/CorpusID:26158108#id-name=S2CID&rft_id=info:pmid/16400143&rft_id=info:bibcode/2006Sci...311...60H&rft.aulast=Huang&rft.aufirst=Xinchuan&rft.au=McCoy,+Anne+B.&rft.au=Bowman,+Joel+M.&rft.au=Johnson,+Lindsay+M.&rft.au=Savage,+Chandra&rft.au=Dong,+Feng&rft.au=Nesbitt,+David+J.&rft_id=https://zenodo.org/record/1230864&rfr_id=info:sid/en.wikipedia.org:Methanium" class="Z3988">
10. ^ Sommer, J.; Jost, R. (2000). "Carbenium and carbonium ions in liquid- and solid-superacid-catalyzed activation of small alkanes" (PDF). Pure and Applied Chemistry. 72 (12): 2309–2318\. doi:10.1351/pac200072122309. S2CID 46627813.
11. ^ a b Field, F. H.; Munson, M. S. B. (1965). "Reactions of gaseous ions. XIV. Mass spectrometric studies of methane at pressures to 2 Torr". Journal of the American Chemical Society. 87 (15): 3289–3294\. doi:10.1021/ja01093a001.

*[CID]: Compound ID