INDEX charge transfer complexes

Brown (1959) has presented a charge transfer model of the transition state for electrophilic reactions which differs appreciably from that proposed by Fukui and his collaborators and leads to the definition of a new reactivity index termed the Z value . The model is based on a more conventional formulation of the charge transfer mechanism, which avoids the complete transfer of electrons associated with v = 0,1,2 in Fukui s model. There is no dependence on the formation of a pseudo tt orbital in the transition state, nor is hyperconjugation invoked. A wave function for a charge transfer complex is written as a linear combination of a wave function < o describing the unperturbed ground state of the molecule under attack, and a function which differs from (Pq in the replacement... 

Here, Ae is the charge transferred from one reactant to the other, t and r2 are the radii of the two (spherical) reactants, r12 is, as before, the center-to-center distance, often approximated18 as the sum of + r2, and Ds and Dop are the static and optical (square of refractive index) dielectric constants of the solvent, respectively. This model for /lout treats both the reactants as hard spheres (i.e., the hard sphere model). For other shapes, more complex models are needed, which are rarely used by reaction chemists.21... 

I. Quantum biochemistry by A. Puixman and B. Pullman. II. Mechanisms of energy transfer by Th. FOrster. III. Char transfer in biology a) Donor-acceptor complexes in solution, (b) Transfer of charge in the organic solid state by F. J. Bullock. IV. Active transport and ion accumulation by P. Mitchell. Subject index. 

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