Sandorfy C model

Figure 11.6. Molecular orbital representations of the HOMO and LUMO of a linear polysilane based on the Sandorfy C model.

In the Sandorfy C model, the degree of delocalization can be appreciated by consideration of the ratio of the resonance integrals p for geminal (same atom)... 

When the parent neutral molecule has well-conjugated electronic orbitals without any interactions with orbitals in other symmetries, we note that the observed absorption transition for the radical cation and anion should be identical. This nature is widely known as the Pairing Theorem ". Concerning the (T-conjugation of the polysilane main chain, this theorem should be closely related to the Sandorfy C and H orbital models la, 15,19). In the case that this theorem is approximately valid, the electronic property of the main chain can be explained by the model C, which is a more simple approximation than the other. 

T. Di Paolo, C. Bourderon, and C. Sandorfy, Model calculations on the influence of mechanical and electrical anharmonicity on infrared intensities Relation to hydrogen bonding. Can. 

A red shift in the absorption maxima and a gradual increase in the molar absorption coefficients (e) can be observed with increasing chain length. This is due to the a-conjugation along the silicon main chain depending on substituent and conformational effects that can be explained by molecular orbital theory (MO). The LCAO, Sandorfy model C and FE (free electron) methods have been used. 

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