Non-classical Cation
   HOME

TheInfoList



OR:

In
chemistry Chemistry is the scientific study of the properties and behavior of matter. It is a physical science within the natural sciences that studies the chemical elements that make up matter and chemical compound, compounds made of atoms, molecules a ...
, 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 In organic chemistry, the term 2-norbornyl cation (or 2-bicyclo .2.1eptyl cation) describes a carbonium ionic derivative of norbornane. A salt of the 2-norbornyl cation was crystallized and characterized by X-ray crystallography confirmed the n ...
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 Nuclear magnetic resonance spectroscopy, most commonly known as NMR spectroscopy or magnetic resonance spectroscopy (MRS), is a spectroscopic technique based on re-orientation of atomic nuclei with non-zero nuclear spins in an external magnetic f ...
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. Siehl , H. U. ''The Conundrum of the (C4H7) Cation: Bicyclobutonium and Related Carbocations'' Adv. Phys. Org. Chem. , 2018, 52, 1-4

/ref>


Further reading

*Brown, H. C. (with commentary by P. v. R. Schleyer) ''The Nonclassical Ion Problem''; Plenum Press:  New York /Springer 197

*Moss, R.A. ''The 2-norbornyl cation: a retrospective'' J. Phys. Org. Chem. 2014 , 27, 374-37


See also

*
2-Norbornyl cation In organic chemistry, the term 2-norbornyl cation (or 2-bicyclo .2.1eptyl cation) describes a carbonium ionic derivative of norbornane. A salt of the 2-norbornyl cation was crystallized and characterized by X-ray crystallography confirmed the n ...
* Neighbouring group participation *
Carbocation Carbocation is a general term for ions with a positively charged carbon atom. In the present-day definition given by the IUPAC, a carbocation is any even-electron cation with significant partial positive charge on a carbon atom. They are further ...
*
Steric effects Steric effects arise from the spatial arrangement of atoms. When atoms come close together there is generally a rise in the energy of the molecule. Steric effects are nonbonding interactions that influence the shape (conformational isomerism, co ...
*
Solvation Solvations describes the interaction of a solvent with dissolved molecules. Both ionized and uncharged molecules interact strongly with a solvent, and the strength and nature of this interaction influence many properties of the solute, includi ...


References

{{reflist Carbocations Ions Organic chemistry