Carbonium ion

In chemistry, carbonium ion is any cation that has a pentavalent carbon atom,[1][2] The name carbonium may also be used for the simplest member of the class, properly called methanium (CH+
5), where the five valences are filled with hydrogen atoms.[3][4][5][6]

The next simplest carbonium ions after methanium have two carbon atoms. Ethynium, or protonated acetylene C
2H+
3, and ethenium C
2H+
5 are usually classified in other families. The ethanium ion C
2H+
7 has been studied as an extremely rarefied gas by infrared spectroscopy.[7] The isomers of octonium (protonated octane, C
8H+
19) have been studied.[8] The carbonium ion has a planar geometry.

In older literature the name "carbonium ion" was used for what is today called carbenium. The current definitions were proposed by the chemist George Andrew Olah in 1972[1] and are now widely accepted.

A stable carbonium ion is the complex pentakis(triphenylphosphinegold(I))methanium (Ph
3PAu)
5C+
, produced by Schmidbauer and others.[9]

Preparation

Carbonium ions can be obtained by treating alkanes with very strong acids.[10] Industrially, they are formed in the refining of petroleum during primary thermal cracking.[11]

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See also
  • Fluxional molecules
  • More carbonium ions called non-classical ions are found in certain norbornyl systems
  • Onium compounds
  • Carbenium ion

References
  1. George Andrew Olah (1972). "Stable carbocations. CXVIII. General concept and structure of carbocations based on differentiation of trivalent (classical) carbenium ions from three-center bound penta- or tetracoordinated (nonclassical) carbonium ions. Role of carbocations in electrophilic reactions". J. Am. Chem. Soc. 94 (3): 808–820. doi:10.1021/ja00758a020.
  2. IUPAC, Compendium of Chemical Terminology, 2nd ed. (the "Gold Book") (1997). Online corrected version:  (2006–) "Carbonium ion". doi:10.1351/goldbook.C00839
  3. Boo, Doo Wan; Lee, Yuan T (1995). "Infrared spectroscopy of the molecular hydrogen solvated carbonium ions, CH+
    5    (H
    2    )
    n     (n = 1–6)"    . The Journal of Chemical Physics. 103 (2): 520. Bibcode:1995JChPh.103..520B. doi:10.1063/1.470138.
  4. Asvany, O.; Kumar P, P.; Redlich, B.; Hegemann, I.; Schlemmer, S.; Marx, D. (2005). "Understanding the Infrared Spectrum of Bare CH5+". Science. 309 (5738): 1219–1222. Bibcode:2005Sci...309.1219A. doi:10.1126/science.1113729. PMID 15994376.
  5. 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.
  6. 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.
  7. Yeh, L. I; Price, J. M; Lee, Yuan T (1989). "Infrared spectroscopy of the pentacoordinated carbonium ion C
    2    H+
    7    ". Journal of the American Chemical Society. 111 (15): 5597. doi:10.1021/ja00197a015.
  8. Seitz, Christa; East, Allan L. L (2002). "Isomers of Protonated Octane, C
    8    H+
    19    ". The Journal of Physical Chemistry A. 106 (47): 11653. Bibcode:2002JPCA..10611653S. doi:10.1021/jp021724v.
  9. George A. Olah (1998). Onium Ions. John Wiley & Sons. ISBN 9780471148777.
  10. Sommer, J; Jost, R (2000). "Carbenium and carbonium ions in liquid- and solid-superacid-catalyzed activation of small alkanes". Pure and Applied Chemistry. 72 (12): 2309. doi:10.1351/pac200072122309.
  11. Office of Energy Efficiency and Renewable Energy, U.S. DOE (2006). "Energy Bandwidth for Petroleum Refining Processes"
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