Side-chain interactions equilibrium constant

STEREOCHEMICAL TERMINOLOGY, lUPAC RECOMMENDATIONS Apical and equatorial ligand interchange, PSEUDOROTATION APICOPHILIOITY APOACTIVATOR Apolar side-chain interactions, HYDROPHOBIC EFFECT Apparent equilibrium constant,... 

The best-known equation of the type mentioned is, of course, Hammett s equation. It correlates, with considerable precision, rate and equilibrium constants for a large number of reactions occurring in the side chains of m- and p-substituted aromatic compounds, but fails badly for electrophilic substitution into the aromatic ring (except at wi-positions) and for certain reactions in side chains in which there is considerable mesomeric interaction between the side chain and the ring during the course of reaction. This failure arises because Hammett s original model reaction (the ionization of substituted benzoic acids) does not take account of the direct resonance interactions between a substituent and the site of reaction. This sort of interaction in the electrophilic substitutions of anisole is depicted in the following resonance structures, which show the transition state to be stabilized by direct resonance with the substituent ... 

In the case of low molecular weight model substances or when only one of the reacting macromolecules is the polymer, the constant K2 is very low, i.e. the reaction (3) is practically displaced to the left-hand side. In the reactions between polymer electrolytes the constant K2 is high due to cooperative interactions of connect functional groups on polymer chains. This leads to a shift of equilibrium (3) to the right-hand side, i.e. to complex formation is favored. 

The model network employed is described in detail in Gao and Weiner [2] and [3], Briefly put, the model chains are freely jointed, and the covalent bonds are represented by a linear, stiff spring of equilibrium length a the noncovalent interaction is the repulsive portion of a Lennard-Jones potential which approximates a hard-sphere interaction of diameter a. The network corresponds to the familiar three-chain model of rubber elasticity (see Treloar [10]). In the reference state, three chains, one in each coordinate direction, have their end atoms fixed in the center of the faces of a cube of side L periodic boundary conditions are employed to remove surface effects as is customary in molecular dynamics simulations. The system is siibjected to a uniaxial deformation at constant volume so that the cube side in the x direction has length XL while the other two sides have lengtn... 

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