In
chemistry
Chemistry is the science, scientific study of the properties and behavior of matter. It is a natural science that covers the Chemical element, elements that make up matter to the chemical compound, compounds made of atoms, molecules and ions ...
, a carbonium ion is any
cation
An ion () is an atom or molecule with a net electrical charge.
The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by convent ...
that has a
pentavalent
In chemistry, the valence (US spelling) or valency (British spelling) of an element is the measure of its combining capacity with other atoms when it forms chemical compounds or molecules.
Description
The combining capacity, or affinity of a ...
carbon
Carbon () is a chemical element with the symbol C and atomic number 6. It is nonmetallic and tetravalent
In chemistry, the valence (US spelling) or valency (British spelling) of an element is the measure of its combining capacity with o ...
atom.
The name carbonium may also be used for the simplest member of the class, properly called
methanium
In chemistry, methanium is a complex positive ion with formula []+, namely a molecule with one carbon atom covalent bond, bonded to three hydrogen atoms and one hydrogen molecule, bearing a +1 electric charge. It is a superacid and one of the ...
(), where the five valences are filled with
hydrogen
Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-toxic, an ...
atoms.
The next simplest carbonium ions after methanium have two carbon atoms.
Ethynium, or protonated
acetylene
Acetylene (systematic name: ethyne) is the chemical compound with the formula and structure . It is a hydrocarbon and the simplest alkyne. This colorless gas is widely used as a fuel and a chemical building block. It is unstable in its pure ...
, and
ethenium
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; ...
are usually classified in other families. The
ethanium
In chemistry, ethanium or protonated ethane is a highly reactive positive ion with formula . It can be described as a molecule of ethane () with one extra proton (hydrogen nucleus), that gives it a +1 electric charge.
Ethanium is one of the s ...
ion has been studied as an extremely rarefied gas by infrared spectroscopy.
The isomers of octonium (protonated octane, ) have been studied. The carbonium ion has a planar geometry.
In older literature, the name "carbonium ion" was used for what is today called
carbenium
A carbenium ion is a positive ion with the structure RR′R″C+, that is, a chemical species with a trivalent carbon that bears a +1 formal charge.
In older literature the name carbonium ion was used for this class, but now it refers exclusivel ...
. The current definitions were proposed by the chemist
George Andrew Olah
George Andrew Olah (born Oláh András György; May 22, 1927 – March 8, 2017) was a Hungarian-American chemist. His research involved the generation and reactivity of carbocations via superacids. For this research, Olah was awarded a Nobel Pr ...
in 1972
and are now widely accepted.
A stable carbonium ion is the complex pentakis(triphenylphosphinegold(I))methanium , produced by Schmidbauer and others.
Preparation
Carbonium ions can be obtained by treating
alkane
In organic chemistry, an alkane, or paraffin (a historical trivial name that also has other meanings), is an acyclic saturated hydrocarbon. In other words, an alkane consists of hydrogen and carbon atoms arranged in a tree structure in which ...
s with very strong acids.
Industrially, they are formed in the refining of petroleum during primary thermal
cracking (Haag-Dessau mechanism).
[Office of Energy Efficiency and Renewable Energy, U.S. DOE (2006)]
"Energy Bandwidth for Petroleum Refining Processes"
/ref>
See also
*Fluxional molecules
In chemistry and molecular physics, fluxional (or non-rigid) molecules are molecules that undergo dynamics such that some or all of their atoms interchange between symmetry-equivalent positions. Because virtually all molecules are fluxional in so ...
*More carbonium ions called non-classical ion
Nonclassical carbocations are stabilized by charge delocalization from contributions of neighbouring or bonds, which can form bridged intermediates or transition states. Nonclassical ions have been extensively studied with the 2-norbornyl sys ...
s are found in certain norbornyl systems
*Onium compounds
In chemistry, an onium ion is a cation formally obtained by the protonation of mononuclear parent hydride of a pnictogen (group 15 of the periodic table), chalcogen (group 16), or halogen (group 17). The oldest-known onium ion, and the namesake ...
*Carbenium ion
A carbenium ion is a positive ion with the structure RR′R″C+, that is, a chemical species with a trivalent carbon that bears a +1 formal charge.
In older literature the name carbonium ion was used for this class, but now it refers exclusivel ...
References
{{Reflist
Reactive intermediates
Carbocations