Pentagonal carbon rings

One main reason for the great interest in the study of fuUerenes is certainly to be found in their particularly appealing geometrical form. The best known fullerene is the so-called buck-minsterfuUerene that contains 60 carbon atoms (Qo) and is composed of 12 pentagonal carbon rings located around the vertices of an icosahedron and 20 hexagonal carbon rings at the centers of icosahedral faces (Kroto et al. 1985). 

Under electron irradiation (or by other mechanisms) it is possible to generate carbon vacancies leading to the formation of extended defect domains (with the presence of pentagonal and heptagonal, and even four-membered carbon rings) showing semiconductor character. This is the mechanism of formation of semiconductor properties in quantum-dot carbon nanoparticles or graphene nanoribbon. The mechanism... 

Figure 8-57. Structure of fullerenes constructed from pentagonal and hexagonal carbon rings.

A 4-carbon ring would form a square, with the angles 90° a 5-carbon ring would form a pentagon with angles 108° a 6-carbon ring would form a hexa-... 

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