Ethenium

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title: "Ethenium" type: doc version: 1 created: 2026-02-28 author: "Wikipedia contributors" status: active scope: public tags: ["carbocations", "physical-chemistry"] topic_path: "science/chemistry" source: "https://en.wikipedia.org/wiki/Ethenium" license: "CC BY-SA 4.0" wikipedia_page_id: 0 wikipedia_revision_id: 0

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In chemistry, ethenium, protonated ethylene or ethyl cation is a positive ion with the formula . It can be viewed as a molecule of ethylene () with one added proton (), or a molecule of ethane () minus one hydride ion (). It is a carbocation; more specifically, a nonclassical carbocation.

Preparation

Ethenium has been observed in rarefied gases subjected to radiation. Another preparation method is to react certain proton donors such as , , , and with ethane at ambient temperature and pressures below 1 mmHg. (Other donors such as and form ethanium preferably to ethenium.)

At room temperature and in a rarefied methane atmosphere, ethanium slowly dissociates to ethenium and . The reaction is much faster at 90 °C.

Stability and reactions

Contrary to some earlier reports, ethenium was found to be largely unreactive towards neutral methane at ambient temperature and low pressure (on the order of 1 mmHg), even though the reaction yielding sec- and is believed to be exothermic.

Structure

The structure of ethenium's ground state was in dispute for many years, but it was eventually agreed to be a non-classical structure, with the two carbon atoms and one of the hydrogen atoms forming a three-center two-electron bond. Calculations have shown that higher homologues, like the propyl and *n-*butyl cations also have bridged structures. Generally speaking, bridging appears to be a common means by which primary carbocations (carbocations with one alkyl group) achieve additional stabilization. Consequently, true primary carbocations (with a classical structure) may be rare or nonexistent.

References

References

  1. Margaret French and Paul Kebarle (1975), "Pyrolysis of {{chem. C. 2. H. 7. + and other ion-molecule reactions in methane containing traces of ethane". Canadian Journal of Chemistry, volume 53, pages 2268-2274. {{doi. 10.1139/v75-318
  2. G. I. Mackay, H. I. Schiff, D. K. Bohme (1981), "A room-temperature study of the kinetics and energetics for the protonation of ethane" Canadian Journal of Chemistry, volume 59, issue 12,pages 1771-1778. {{doi. 10.1139/v81-265
  3. F. H. Field , M. S. B. Munson (1965), "Reactions of gaseous ions. XIV. Mass spectrometric studies of methane at pressures to 2 Torr". Journal of the American Chemical Society, volume 87, issue 15, pages 3289–3294 {{doi. 10.1021/ja01093a001

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carbocationsphysical-chemistry