Why -OH groups readily soluble in water? If the hydrogen bonds are relatively strong, shouldn't they be less soluble?
The OH^- ion is polarized. Water molecules are polarized. Like dissolves like.
The solubility of -OH groups in water can be attributed to the polar nature of both the -OH group and water molecules. The -OH group contains an electronegative oxygen atom bonded to a hydrogen atom. Because oxygen is more electronegative than hydrogen, it pulls the shared electrons closer to itself, resulting in a partial negative charge (δ-) on the oxygen atom and a partial positive charge (δ+) on the hydrogen atom.
Water molecules also have a similar arrangement of electronegative oxygen atoms bonded to hydrogen atoms, resulting in partial negative charges on the oxygen atoms and partial positive charges on the hydrogen atoms. This creates an opportunity for hydrogen bonding to occur between water molecules and the -OH group.
Hydrogen bonding is a strong dipole-dipole interaction where the δ+ hydrogen atom of one molecule is attracted to the δ- oxygen atom of another molecule. In the case of -OH groups, the hydrogen bonding occurs between the hydrogen atom of the -OH group and the oxygen atoms of neighboring water molecules.
When an -OH group dissolves in water, the polar water molecules surround the -OH group, with the partially negative oxygen atoms in water forming hydrogen bonds with the partially positive hydrogen atom of the -OH group. This allows water molecules to effectively "shield" the charged -OH group, preventing it from rejoining and forming solid aggregates. Instead, the interactions between water molecules and -OH groups throughout the solution help stabilize the solvated -OH ions, resulting in their high solubility in water.
In summary, the solubility of -OH groups in water is primarily due to the ability of water molecules to form hydrogen bonds with the -OH group's hydrogen atom, allowing for effective "dissolution" and solvation of the -OH ions within the water system.