The heats of solution from the pure liquid state to dilute solution in water have been measured for three series of substituted n-alkanes, the n-alkyl methyl sulphoxides, the di-n-alkyl sulphoxides and the α,ω-alkane diols. The effect of a methylene group on the heat of solution depends on its proximity to the polar group. For a methylene group removed from the influence of a polar group the heat of solution is 500 ± 100 cal mole–1.