Spurious Cooperativity in Some Alkylated Succinic Acids

Spurious Cooperativity in Some Alkylated Succinic Acids 

As we have noted in previous subsections, at present it is not possible to reproduce the experimental values of fcj, kj, and g(l, 1) for these compounds. The main difficulty is to account for the solvent effects, which cannot be ignored in these molecules. In spite of this limitation we shall see below that the phenomenon of spurious cooperativity can explain the two major observations first, the decrease in g(l, 1) by five to six orders of magnimde upon increasing the alkyl substituent in the racemic series, and second, that these changes occur only in the racemic and not in the meso form. 

The model used for the a-a dialkyl succinic acid is essentially an extension of the model used in the previous subsection. Here, instead of the two hydrogens on the C -carbones we have one alkyl group R on each of the C carbones, as shown in Fig. 4.30. 

Thermodynamic Dissociation Constants for Alkylated Succinic Acids in 50% Aqueous Ethanol 

The essential simplification of the model is to replace the alkyl substituents, from mediyl to tert-butyl, by Lennard-Jones spheres of increasing diameters. In this model we cannot calculate the exact values of k and 2 (in fact, these cannot be calculated even if we had the true rotational potential the main missing information is the solvation Gibbs energies of the molecules involved). Nevertheless, we can demonstrate with this simplified model the two major experimental findings regarding the proton-proton correlation in these series of molecules, as shown in Table 4.6. 

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