Molecular Orbital Theory of Periodic Systems

We have already seen (Chapters 8 and 13) that the orbital energies, degeneracies, and coefficients in benzene are to a great extent determined by symmetry. But these symmetry constraints can also be viewed as resulting from the cyclic periodicity of benzene, and this finite cyclic periodicity is, in essential ways, like the extended infinite periodicity of, say, regular polyacetylene or of graphite. It is reasonable, therefore, that some of the aspects of the energies and orbitals in these extended periodic stmctures are closely related to those in cyclic periodic systems. [Pg.526]

The concepts commonly used to describe periodic polymers, surfaces, or solids are closely related to those we have already developed for molecules, but their terminology and depiction are not familiar to most chemists. Our goal in this chapter is to develop an understanding of these concepts by progressing from more familiar cyclic systems, like benzene, to polymers, and to show how qualitative MO concepts apply to periodic systems in general. [Pg.526]

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