Charge transfer , molecular orbital

Forty-nine classes describing the H, C, N, O, and S atoms in different molecules interacting with water have been developed. These classes can be transferred to other molecules, provided that each atom in the solute and its nearest neighbors have previously been studied (Bolis and dementi, 1977). Net charge and molecular orbital valency state energy are used to assign atoms with the same atomic number to different classes (Carozzo et al., 1978 Corongiu et al., 1979). 

The last system investigated by the deformation-potential method is a member of the large family of charge-transfer molecular crystals containing as anion the tetracyanoquinodimethane (TCNQ) molecule. The K TCNQ" salt as well as the other TCNQ crystals consist of columns of stacked TCNQ molecules coordinated by similar columns of the cations. The energy band structures of the stack have been calculated earlier with the help of Pariser-Parr-Pople parametrization of the unrestricted Hartree-Fock crystal-orbital method The last two columns of Table 9.10 show that this material behaves again as a normal... 

The charge transfer term arises from the transfer of charge (i.e. electrons) from occupied molecular orbitals on one molecule to unoccupied orbitals on the other molecule. This contribution is calculated as the difference between the energy of the supermolecule XY when this charge transfer is specifically allowed to occur, and an analogous calculation in which it is not. 

Carrier generators in molecular conductors have been associated for a long time to a partial charge transfer between the HOMO (or LUMO) electronic band and other chemical species. These systems are known as two-component molecular conductors. Tetrathiofulvalene derivatives are versatile systems for the formation of molecular organic conductors due to their electron donor capacity by transferring one u-electron from the HOMO orbital, and to their planar shape that promotes their stacking as a consequence of the n-n orbital overlap. The electronic properties of these salts are essentially determined by the packing pattern of the donor molecules which, in turn, depends on the counter-ion. 

Semi-empirical molecular orbital calculations have been carried out on the model phosphorane HaPiCHa. Besides the expected transfer of charge, the inclusion of the phosphorus 2>d orbitals showed a significant hyperconjugative interaction between the CHg orbitals and a 2>d orbital of appropriate symmetry on phosphorus. Calculations on cyclopropylidene-phosphorane revealed a similar interaction between the Walsh orbitals of the ring and an in-plane phosphorus 2>d orbital. 

Charge-Transfer Spectra and Molecular Orbital Calculations. 

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