# Question #20ab2

Sep 25, 2016

Alkanes have no functional group that can be effectively solvated by the water molecule. On the other hand, an aldehyde possesses a terminal carbonyl group $R C \left(= O\right) H$ that can be solvated by water to allow some solubility. On the other, other hand, short chain alcohols, methanol, and ethanol, are effectively half a water molecule, and the influence of the hydroxyl group dictates their miscibility with water.
From the earliest lessons in chemistry, we learn that $\text{like dissolves like}$. This is certainly illustrated by the water solubility of $\text{ethane}$, which is much less water soluble than $\text{acetaldehyde}$, which is much less water soluble than $\text{ethanol}$.
As the chain length of the alcohol grows, the solubility of $R O H$ will likewise DECREASE in water, as the interaction between the hydrocarbyl tails becomes significant. On the other hand, while $\text{ethanol}$ is miscible with hexanes, $\text{methanol}$ is immiscible with this solvent, and will form a layer below the hydrocarbon, just as water would. Can you account for these phenomena?