Spherical Homoaromaticity
Zhongfang Chen, Haijun Jiao, Andreas Hirsch, Paul von Ragué Schleyer · Angewandte Chemie International Edition · 2002
The 2(N+1)2 electron-counting rule for spherical aromaticity can also be applied to spherical homoaromatic systems: The adamantane-, cubane-, and dodecahedrane-based species containing two or eight delocalized electrons were designed by bridging the sp2 carbon atoms of highly symmetrical (Td, Th) carbon polyhedrane units. Their aromatic character was demonstrated by the highly negative nucleus-independent chemical shift (NICS) values at the cage centers, for example C20H12 (see picture) has an NICS value of −36.4 ppm.