Delocalization electrons responsibilities

Experimental pK data suggest that eyano substitution can exert substantial long-range effeets on phenol aeidity, but the reason for these effeets is not obvious. If ion-dipole interaetions were to blame, the effeet would fall off with increasing ion (0 ) - dipole (CN) separation. If electron delocalization were responsible, then the effeet would be aeeompanied by eharge transfer between the ionie site (O ) and other atoms in the moleeule. 

In band theory the electrons responsible for conduction are not linked to any particular atom. They can move easily throughout the crystal and are said to be free or very nearly so. The wave functions of these electrons are considered to extend throughout the whole of the crystal and are delocalized. The outer electrons in a solid, that is, the electrons that are of greatest importance from the point of view of both chemical and electronic properties, occupy bands of allowed energies. Between these bands are regions that cannot be occupied, called band gaps. 

Metals have a sea of delocalized electrons that are not bound to specific nuclei, and these are responsible for both their high electrical and heat conductivities. Organic compounds do not ordinarily have such delocalized electrons, and are poor electrical and heat conductors. In fact, they are used to coat electrical wires as insulators. If polymers can be made to conduct, then they could be of a great deal of utility, as they are light, can be processed at low temperatures and pressures, and the raw material does not depend on metal mining. However, the possibility of a conducting polymer did not arise till very recent times. 

Charge delocalization pathways were gauged and compared on the basis of the magnitude of A8 C values. Some representative examples are shown in Fig. 8. It was concluded that the carboxonium group is a robust electron-withdrawing substituent whose electronic response is sensitive to steric factors. In this way, it could be used to modulate charge delocalization into PAHs and their carbocations, as a function of substitution position. 

Conjugated conducting polymers consist of a backbone of resonance-stabilized aromatic molecules. Most frequently, the charged and typically planar oxidized form possesses a delocalized -electron band structure and is doped with counteranions (p-doping). The band gap (defined as the onset of the tt-tt transition) between the valence band and the conduction band is considered responsible for the intrinsic optical properties. Investigations of the mechanism have revealed that the charge transport is based on the formation of radical cations delocalized over several monomer units, called polarons [27]. 

The TT-electron states are true many-body states because electron correlations due to natural repulsive Coulomb interactions tend to localize the otherwise delocalized electrons. Electron correlations play an important role in the nonlinear optical responses of conjugated organic structures (1-3,16,17,26), and their description of 3 and Y i l differs markedly from inde-... 

In metals, the bonding is predominantly metallic, where delocalized electrons provide the glue that holds the positive ion cores together. This delocalization of the bonding electrons has far-reaching ramifications since it is responsible for properties most associated with metals ductility, thermal and electrical conductivity, reflectivity, and other distinctive properties. 

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