Structural features and aqueous solubility

Interactions between nonpolar groups and water were discussed above, where the importance of both size and shape was indicated. Chain branching of hydrophobic groups influences aqueous solubility, as shown by the solubilities of a series of straight and branched-chain alcohols in Table 5.2. 

As boiling points of liquids and melting points of solids are indicators of molecular 

The influence of substituents on the solubility of molecules in water can be due to their effect on the properties of the solid or liquid (for example, on its molecular cohesion) or to the effect of the substituent on its interaction with water molecules. It is not easy to predict what effect a particular substituent will have on crystal properties, but as a guide to the solvent interactions, substituents can be classified as either hydrophobic or hydrophilic, depending on their polarity (see Table 5.4). The position of the substituent on the molecule can influence its effect, however. This can be seen in the aqueous solubilities of o-, m- and p-dihydroxy-benzenes as expected, all are much greater than that of benzene, but they are not the same, being 4, 9 and 0.6 mol dm, respectively. The relatively low solubility of the para compound is due to the greater stability of its crystalline state. The melting points of the derivatives indicate that is so, as they are 105°C, 111°C, and IZO C, respectively. In the case of the ortho 

Compound Solubility (mol kg- ) Surface area (nm2) Boiling point ( C) Predicted solubilities (mol kg- ) 

Compound Solubility Surface area (molality, m) (nm ) Boiling point PC) Structure 

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