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 matter, organic materials, i.e., matter in its various forms that contain ...

, spherical aromaticity is formally used to describe an unusually stable nature of some spherical compounds such as

fullerene A fullerene is an allotropes of carbon, allotrope of carbon whose molecules consist 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 six atoms. The molecules may ...

s and polyhedral

boranes A borane is a compound with the formula although examples include multi-boron derivatives. A large family of boron hydride clusters is also known. In addition to some applications in organic chemistry, the boranes have attracted much attention ...

. In 2000, Andreas Hirsch and coworkers in

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, formulated a rule to determine when a spherical compound would be

aromatic In organic chemistry, aromaticity is a chemical property describing the way in which a conjugated system, conjugated ring of unsaturated bonds, lone pairs, or empty orbitals exhibits a stabilization stronger than would be expected from conjugati ...

. They found that those with 2(''n''+1)² π-

electrons The electron (, or in nuclear reactions) is a subatomic particle with a negative one elementary charge, elementary electric charge. It is a fundamental particle that comprises the ordinary matter that makes up the universe, along with up qua ...

could display aromatic properties, as spherical molecular orbitals are filled when there are 2(''n''+1)² π-electrons for some positive integer ''n''. For example, in

buckminsterfullerene Buckminsterfullerene is a type of fullerene with the formula . It has a cage-like fused-ring structure ( truncated icosahedron) made of twenty hexagons and twelve pentagons, and resembles a football. Each of its 60 carbon atoms is bonded to i ...

(C₆₀) this happens for the species C₆₀¹⁰⁺, which has 50 π-electrons: 50/2 = 25, which is a perfect square. In 2011, Jordi Poater and Miquel Solà expanded Hirsch's rule to open-shell spherical compounds, which have unfilled outer shells but are still aromatic. They found that spherical compounds with 2''n''²+2''n''+1 π-

with

spin Spin or spinning most often refers to: * Spin (physics) or particle spin, a fundamental property of elementary particles * Spin quantum number, a number which defines the value of a particle's spin * Spinning (textiles), the creation of yarn or thr ...

S = (n + 1/2) would also display aromatic properties, sometimes more aromatic than comparable closed-shell species. This corresponds to the outer shell being half-filled,. and is similar to

Baird's rule In organic chemistry, Baird's rule estimates whether the lowest triplet state of planar, cyclic structures will have aromatic properties or not. The quantum mechanical basis for its formulation was first worked out by physical chemist N. Colin ...

. For example buckminsterfullerene with one additional electron, (C₆₀^1–) is aromatic, with S = 11/2 and a bond-length alternation of 0.2 pm.

References

External links

Spherical Aromaticity: Recent Work on Fullerenes, Polyhedral Boranes, and Related Structures
{{Chemical bonds Physical organic chemistry Supramolecular chemistry

See also

References

External links