In
organic chemistry
Organic chemistry is a subdiscipline within chemistry involving the science, scientific study of the structure, properties, and reactions of organic compounds and organic materials, i.e., matter in its various forms that contain carbon atoms.Clay ...
, spherical aromaticity is formally used to describe an unusually stable nature of some spherical compounds such as
fullerene
A fullerene is an allotrope of carbon whose molecule consists of carbon atoms connected by single and double bonds so as to form a closed or partially closed mesh, with fused rings of five to seven atoms. The molecule may be a hollow sphere, ...
s, polyhedral
boranes
Boranes is the name given to compounds with the formula BxHy and related anions. Many such boranes are known. Most common are those with 1 to 12 boron atoms. Although they have few practical applications, the boranes exhibit structures and bon ...
.
In 2000, Andreas Hirsch and coworkers in
Erlangen
Erlangen (; East Franconian: ''Erlang'', Bavarian: ''Erlanga'') is a Middle Franconian city in Bavaria, Germany. It is the seat of the administrative district Erlangen-Höchstadt (former administrative district Erlangen), and with 116,062 inhabi ...
,
Germany
Germany, officially the Federal Republic of Germany (FRG),, is a country in Central Europe. It is the most populous member state of the European Union. Germany lies between the Baltic and North Sea to the north and the Alps to the sou ...
, formulated a rule to determine when a
fullerene
A fullerene is an allotrope of carbon whose molecule consists of carbon atoms connected by single and double bonds so as to form a closed or partially closed mesh, with fused rings of five to seven atoms. The molecule may be a hollow sphere, ...
would be
aromatic
In chemistry, aromaticity is a chemical property of cyclic (ring-shaped), ''typically'' planar (flat) molecular structures with pi bonds in resonance (those containing delocalized electrons) that gives increased stability compared to sat ...
. They found that if there were 2(''n''+1)
2 π-
electrons
The electron (, or in nuclear reactions) is a subatomic particle with a negative one elementary electric charge. Electrons belong to the first generation of the lepton particle family,
and are generally thought to be elementary partic ...
, then the fullerene would display aromatic properties. This follows from the fact that an aromatic fullerene must have full
icosahedral (or other appropriate) symmetry, so the molecular orbitals must be entirely filled. This is possible only if there are exactly 2(''n''+1)
2 electrons, where ''n'' is a nonnegative integer. In particular, for example,
buckminsterfullerene
Buckminsterfullerene is a type of fullerene with the formula C60. It has a cage-like fused-ring structure (truncated icosahedron) made of twenty hexagons and twelve pentagons, and resembles a soccer ball. Each of its 60 carbon atoms is bonded ...
, with 60 π-electrons, is non-aromatic, since 60/2 = 30, which is not a
perfect square
''Perfect Square'' is a 2004 concert film of the alternative rock Musical ensemble, band R.E.M. (band), R.E.M., filmed on July 19, 2003, at the bowling green, Bowling Green in Wiesbaden, Germany. It was released by Warner Reprise Video on March 9, ...
.
In 2011, Jordi Poater and Miquel Solà, expanded the rule to determine when an open-shell
fullerene
A fullerene is an allotrope of carbon whose molecule consists of carbon atoms connected by single and double bonds so as to form a closed or partially closed mesh, with fused rings of five to seven atoms. The molecule may be a hollow sphere, ...
species would be aromatic. They found that if there were 2''n''
2+2''n''+1 π-
electrons
The electron (, or in nuclear reactions) is a subatomic particle with a negative one elementary electric charge. Electrons belong to the first generation of the lepton particle family,
and are generally thought to be elementary partic ...
, then the fullerene would display aromatic properties. This follows from the fact that a spherical species having a same-spin half-filled last energy level with the whole inner levels being fully filled is also aromatic.
[.] It is similar to
Baird's rule.
See also
*
Fullerene chemistry
*
Carborane
*
Boranes
Boranes is the name given to compounds with the formula BxHy and related anions. Many such boranes are known. Most common are those with 1 to 12 boron atoms. Although they have few practical applications, the boranes exhibit structures and bon ...
References
External links
Spherical Aromaticity: Recent Work on Fullerenes, Polyhedral Boranes, and Related Structures
{{Chemical bonds
Physical organic chemistry
Supramolecular chemistry