Quantitative antihydrophobic effect

Breslow R, Zhu Z. Quantitative antihydrophobic effects as probes for transition state structures. J Am Chem Soc 1995 117 9923-9924. 

Quantitative antihydrophobic effects in water and the geometries of transition states... 

R. Breslow, S. Halfon, Quantitative effects of antihydrophobic agents on binding constants and solubihties in water, Proc. Natl. Acad. Sci. USA, 1992, 89, 6916-6918. 

Throughout this account we have been using antihydrophobic additives such as guanidinium cation or alcohols to show that there was some hydrophobic overlap in the transition states of various reactions. We realized that this could be made quantitative - the magnitude of the effect of the antihydrophobic additive on a rate could be related to the amount of hydrophobic surface that becomes hidden from the water in the transition state. This work was reviewed recently. 

From the slope of the plot, we could see that about 40% of one face of each phenyl group is inaccessible to water solvent in the transition state. We will return to such quantitative calculations later. In that paper, we also examined the effect of antihydrophobic additives on the rates of some displacement reactions, such as the reaction of N-methylaniline with the sodium salt of p-carboxybenzyl chloride (the carboxylate group was added to achieve water solubility). We must return later to such displacement reactions to see how much the additives affect the solvation of charges in these cases. 

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