Linear solvation energy relationships. 41. Important differences between aqueous solubility relationships for aliphatic and aromatic solutes

Aqueous solubility relationships of aromatic and aliphatic solutes differ from one another in two important regards: (a) Solubilities of aliphatic solutes do and those of aromatic solutes do not show important dependences on solute dipolarity/polarizability (as measured by the solvatochromic parameter, π*), and (b) dependences on the solute hydrogen bond acceptor basicity parameter, β, are about one-fourth smaller for aromatic than for aliphatic solutes. Solubilities of 70 liquid and solid aromatic solutes containing up to three fused rings are well correlated by the equation: log S_w = 0.57 - 5.58V_I/100 + 3.85β - 0.0110(mp - 25); r = 0.9917, sd = 0.216. V_I is the computer calculated intrinsic (van der Waals) molar volume. Liquid aliphatic solutes follow a rather different relationship: log S_w = 0.05 - 5.85V_I/199 + 1.09π* + 5.23β n = 115, r = 0.9944, sd = 0.153. The differences between aliphatic and aromatic solutes may be due, in part, to "vertical stacking" in aromatic liquids.