Nonclassical ion

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Type of molecule in organic chemistry

title: "Nonclassical ion" type: doc version: 1 created: 2026-02-28 author: "Wikipedia contributors" status: active scope: public tags: ["carbocations", "ions", "organic-chemistry"] description: "Type of molecule in organic chemistry" topic_path: "science/chemistry" source: "https://en.wikipedia.org/wiki/Nonclassical_ion" license: "CC BY-SA 4.0" wikipedia_page_id: 0 wikipedia_revision_id: 0

::summary Type of molecule in organic chemistry ::

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In chemistry, a nonclassical ion usually refers to carbonium ions, a family of organic cations. They are characterized by delocalized three-center, two-electron bonds. The more stable members are often bi- or polycyclic.

Examples

Historically, nonclassical ions were invoked to explain unusually fast solvolyses of steroidal, norbornyl, and cyclopropyl halides. Explanations for these rates was once controversial.

The 2-norbornyl cation is one of the best characterized carbonium ions: : In fact, it has emerged as the prototype for non-classical ions. As indicated first by low-temperature NMR spectroscopy and confirmed by X-ray crystallography, it has a symmetric structure with an RCH2+ group bonded to an alkene group, stabilized by a bicyclic structure.

Solvolyses of cyclopropylcarbinyl, cyclobutyl, and homoallyl esters are also characterized by very large rates, and have been shown to occur via a common nonclassical ion structure in the form of a bicyclobutonium ion.

References

References

  1. (2013-07-05). "Crystal Structure Determination of the Nonclassical 2-Norbornyl Cation". Science.
  2. Thomas H. Lowery. (1981). "Mechanism and Theory in Organic Chemistry, Second Edition". Harper and Rowe.
  3. Anslyn, E.V., Dougherty, D.A ''Modern Physical Organic Chemistry'' University Science Books '''2005'''[http://www.uscibooks.com/adfm_new.pdf]
  4. Sykes P. ''A guide book to mechanism in organic chemistry'' 6th Ed., New Delhi: Orient Longman, 1986, p. 111 ff [http://about.mdma.ch/picproxie_docs/000536454-Guidebook_to_Mechanism_in_Organic_Chemistry.pdf]
  5. Capon, B., McManus, S. P. ''Neighboring Group Participation'' Vol. 1, Plenum, New York, 1976 [https://link.springer.com/content/pdf/bfm%3A978-1-4684-0826-3%2F1.pdf]
  6. Schneider, H.-J. ''The Controversy about Nonclassical Ions – Abandoned too Early?'' J. Phys. Org. Chem. '''2018''',[https://onlinelibrary.wiley.com/doi/10.1002/poc.3846]
  7. Saunders, M., Laidig, K.E., Wiberg, K.B., Schleyer ''Structures, energies, and modes of interconversion of {{chem2. C4H7+ ions'' J. Am. Chem. Soc., 1988, 110, 7652–7659 [https://pubs.acs.org/doi/pdf/10.1021/ja00231a012]
  8. Siehl, H. U. ''The Conundrum of the (C4H7) Cation: Bicyclobutonium and Related Carbocations'' Adv. Phys. Org. Chem., 2018, 52, 1-47 [https://www.elsevier.com/books/advances-in-physical-organic-chemistry/williams/978-0-12-815211-9]

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