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Methenium
Ion

In organic chemistry, methenium (also called methylium, carbenium, methyl cation, or protonated methylene) is a cation with the formula CH+3. It can be viewed as a methylene radical (:CH2) with an added proton (H+), or as a methyl radical (•CH3) with one electron removed. It is a carbocation and an enium ion, making it the simplest of the carbenium ions.

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Structure

Experiments and calculations generally agree that the methenium ion is planar, with threefold symmetry.3 The carbon atom is a prototypical (and exact) example of sp2 hybridization.

Preparation and reactions

For mass spectrometry studies at low pressure, methenium can be obtained by ultraviolet photoionization of methyl radical,4 or by collisions of monatomic cations such as C+ and Kr+ with neutral methane.5 In such conditions, it will react with acetonitrile CH3CN to form the ion (CH3)2CN+.6

Upon capture of a low-energy electron (less than 1 eV), it will spontaneously dissociate.7

It is seldom encountered as an intermediate in the condensed phase. It is proposed as a reactive intermediate that forms upon protonation or hydride abstraction of methane with FSO3H-SbF5. The methenium ion is very reactive, even towards alkanes.8

Detection

Main article: List of interstellar and circumstellar molecules

Origins of life

Main article: Abiogenesis

In June 2023, astronomers detected, for the first time outside the Solar System, methyl cation, CH3+ (and/or carbon cation, C+), the known basic ingredients of life, in interstellar space.910

See also

References

  1. "Ions, Free Radicals, and Radical-Ion", Nomenclature of Organic Compounds, Advances in Chemistry, vol. 126, AMERICAN CHEMICAL SOCIETY, June 1974, pp. 216–224, doi:10.1021/ba-1974-0126.ch028, ISBN 978-0841201910 978-0841201910 ↩

  2. Golob, L.; Jonathan, N.; Morris, A.; Okuda, M.; Ross, K.J. (1972). "The first ionization potential of the methyl radical as determined by photoelectron spectroscopy". Journal of Electron Spectroscopy and Related Phenomena. 1 (5). Elsevier BV: 506–508. doi:10.1016/0368-2048(72)80022-7. ISSN 0368-2048. /wiki/Doi_(identifier) ↩

  3. Golob, L.; Jonathan, N.; Morris, A.; Okuda, M.; Ross, K.J. (1972). "The first ionization potential of the methyl radical as determined by photoelectron spectroscopy". Journal of Electron Spectroscopy and Related Phenomena. 1 (5). Elsevier BV: 506–508. doi:10.1016/0368-2048(72)80022-7. ISSN 0368-2048. /wiki/Doi_(identifier) ↩

  4. Golob, L.; Jonathan, N.; Morris, A.; Okuda, M.; Ross, K.J. (1972). "The first ionization potential of the methyl radical as determined by photoelectron spectroscopy". Journal of Electron Spectroscopy and Related Phenomena. 1 (5). Elsevier BV: 506–508. doi:10.1016/0368-2048(72)80022-7. ISSN 0368-2048. /wiki/Doi_(identifier) ↩

  5. Sharma, R. B.; Semo, N. M.; Koski, W. S. (1987). "Dynamics of the reactions of methylium, methylene radical cation, and methyliumylidene with acetylene". The Journal of Physical Chemistry. 91 (15). American Chemical Society (ACS): 4127–4131. doi:10.1021/j100299a037. ISSN 0022-3654. /wiki/Doi_(identifier) ↩

  6. McEwan, Murray J.; Denison, Arthur B.; Huntress, Wesley T.; Anicich, Vincent G.; Snodgrass, J.; Bowers, M. T. (1989). "Association reactions at low pressure. 2. The methylium/methyl cyanide system". The Journal of Physical Chemistry. 93 (10). American Chemical Society (ACS): 4064–4068. doi:10.1021/j100347a039. ISSN 0022-3654. /wiki/Doi_(identifier) ↩

  7. Bahati, E. M.; Fogle, M.; Vane, C. R.; Bannister, M. E.; Thomas, R. D.; Zhaunerchyk, V. (2009-05-11). "Electron-impact dissociation of CD+3 and CH+3 ions producing CD+2, CH+ and C+ fragment ions". Physical Review A. 79 (5). American Physical Society (APS): 052703. doi:10.1103/physreva.79.052703. ISSN 1050-2947. /wiki/Doi_(identifier) ↩

  8. Hogeveen, H.; Lukas, J.; Roobeek, C. F. (1969). "Trapping of the methyl cation by carbon monoxide; formation of acetic acid from methane". Journal of the Chemical Society D: Chemical Communications (16): 920. doi:10.1039/c29690000920. ISSN 0577-6171. /wiki/Doi_(identifier) ↩

  9. Sauers, Elisha (27 June 2023). "Webb telescope just found something unprecedented in the Orion Nebula - Astronomers are excited about the detection of a special molecule in space". Mashable. Archived from the original on 27 June 2023. Retrieved 27 June 2023. https://mashable.com/article/james-webb-space-telescope-orion-nebula ↩

  10. Berné, Olivier; et al. (26 June 2023). "Formation of the Methyl Cation by Photochemistry in a Protoplanetary Disk". Nature. 621 (7977): 56–59. arXiv:2401.03296. doi:10.1038/s41586-023-06307-x. hdl:1887/3716674. PMID 37364766. S2CID 259260435. Archived from the original on 27 June 2023. Retrieved 27 June 2023. https://www.nature.com/articles/s41586-023-06307-x ↩