How does water interact with non-polar molecules?
• The problem here is that in order to dissolve in water a non-polar molecule must disrupt a series of H-bonds and no new bonds of equal strength are substituted. • Thus water tends to exclude non-polar substances. When we forcefully disperse a non-polar substance into water then the water must form a cage around the molecule to maximize H-bonds for each water molecule. [text Figure 2-7a] • Now an additional problem arises-the waters hydrating the non-polar group are “locked” in place – they can’t easily flip about because there is no interior bond for substitution! • Thus the entropy of these water molecules is greatly reduced. So the insolubility of non-polar groups in water has both enthalpic and entropic factors! • Note that many non-polar molecules may dissolve in water by the formation of micelles as in text Figure 2-7b. Finally, recall that water is a good nucleophile and so will participate in many chemical reactions-readily hydrolyzes esters, amides, anhydrides etc.
