Methenium

In organic chemistry, methenium (also called methylium, carbenium,[1] methyl cation, or protonated methylene) is a cation with the formula CH+
3
. It can be viewed as a methylene radical (:CH
2
) with an added proton (H+
), or as a methyl radical (•CH
3
) with one electron removed. It is a carbocation and an enium ion, making it the simplest of the carbenium ions.[2]

Methenium
Methyl cation.svg
Names
IUPAC name
Carbanylium
Other names
Methyl cation; Methylium
Identifiers
3D model (JSmol)
ChEBI
UNII
Properties
CH3
Molar mass 15.035 g·mol−1
Related compounds
borane
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references

StructureEdit

Experiments and calculations generally agree that the methenium ion is planar, with threefold symmetry.[2] The carbon atom is a prototypical (and exact) example of sp2 hybridization.

Preparation and reactionsEdit

For mass spectrometry studies at low pressure, methenium can be obtained by ultraviolet photoionization of methyl radical,[2] or by collisions of monatomic cations such as C+
and Kr+
with neutral methane.[3] In such conditions, it will react with acetonitrile CH
3
CN
to form the ion (CH
3
)
2
CN+
.[4]

Upon capture of a low-energy electron (less than eV), it will spontaneously dissociate.[5]

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.[6]

ReferencesEdit

  1. ^ "Ions, Free Radicals, and Radical-Ion", Nomenclature of Organic Compounds, Advances in Chemistry, 126, AMERICAN CHEMICAL SOCIETY, June 1974, pp. 216–224, doi:10.1021/ba-1974-0126.ch028, ISBN 978-0841201910
  2. ^ a b c L. Golob, N. Jonathan, A. Morris, M. Okuda, K.J. Ross (1972), "The first ionization potential of the methyl radical as determined by photoelectron spectroscopy". Journal of Electron Spectroscopy and Related Phenomena, volume 1, issue 5, pp. 506–508 doi:10.1016/0368-2048(72)80022-7
  3. ^ R.B. Sharma, N.M. Semo, W.S. Koski (1987), "Dynamics of the reactions of methylium, methylene radical cation, and methyliumylidene with acetylene". Journal of Physical Chemistry, volume 91, issue 15, pp. 4127–4131 doi:10.1021/j100299a037
  4. ^ Murray J. McEwan, Arthur B. Denison, Wesley T. Huntress Jr., Vincent G. Anicich, J. Snodgrass, M.T. Bowers (1989), "Association reactions at low pressure. 2. The methylium/methyl cyanide system". Journal of Physical Chemistry, volume 93, issue 10, pp. 4064–4068. doi:10.1021/j100347a039
  5. ^ E.M. Bahati, M. Fogle, C.R. Vane, M.E. Bannister, R.D. Thomas and V. Zhaunerchyk (2009), "Electron-impact dissociation of CD+
    3
    and CH+
    3
    ions producing CD+
    2
    , CH+
    and C+
    fragment ions". Physical Review, volume 79, article 052703 doi:10.1103/PhysRevA.79.052703
  6. ^ 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. 0 (16): 920. doi:10.1039/c29690000920. ISSN 0577-6171.