Substituent effects on intermolecular hydrogen bonding from a lattice gas theory for lower critical solution points: Comparison with experiments on aqueous solutions of alkylpyridines

The lattice-gas models of reentrant phase transitions in binary mixtures with hydrogen bonding, introduced and studied by Walker, Vause, and Goldstein, are shown to be sensitive to subtle changes in the molecular properties of the mixture components. Specifically, the phase equilibria in aqueous mixtures of alkylpyridines (methyl, dimethyl, and ethyl) are matched with the theoretical parameters describing the strength and orientational specificity of the intermolecular hydrogen bonding. The parametric trends are found to agree with those expected from consideration of the electronic and steric effects of ortho-, meta-, and para-alkyl substitution in aromatic compounds. These trends also correlate well with other thermodynamic and kinetic data on these alkylpyridines. Critical exponent renormalization in these systems is also discussed.