Spherical aromaticity

In <a href="/facts/Organic_chemistry/djxhxaNg">organic chemistry</a>, spherical aromaticity is formally used to describe an unusually stable nature of some spherical compounds such as <a href="/facts/Fullerene/LPdnl8ox">fullerenes</a> and polyhedral <a href="/facts/Boranes/wu3RTzUS">boranes</a>.
In 2000, Andreas Hirsch and coworkers in <a href="/facts/Erlangen/rsTkdwDp">Erlangen</a>, <a href="/facts/Germany/paluuWBX">Germany</a>, formulated a rule to determine when a spherical compound would be <a href="/facts/Aromaticity/wK0DzRY6">aromatic</a>. They found that those with 2(n+1)2 π-<a href="/facts/Electrons/L0KBo5cW">electrons</a> could display aromatic properties, as spherical molcular orbitals are filled when there are 2(n+1)2 π-electrons for some positive integer n. For example, in <a href="/facts/Buckminsterfullerene/F0VebtPK">buckminsterfullerene</a> (C60) this happens for the species C6010+, which has 50 π-electrons: 50/2 = 25, which is a <a href="/facts/Square_number/jfakASPK">perfect square</a>.
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 2n2+2n+1 π-<a href="/facts/Electrons/L0KBo5cW">electrons</a> with <a href="/facts/Spin_(physics)/4Jvp7e8P">spin</a> 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 <a href="/facts/Baird%2527s_rule/CxEhdWJI">Baird's rule</a>. For example buckminsterfullerene with one additional electron, (C601–) is aromatic, with S = 11/2 and a bond-length alternation of 0.2 <a href="/facts/Picometre/Cb54mVBX">pm</a>.

Spherical aromaticity open-in-new

Spherical aromaticity