Examine the structures of phenol and naphthol shown here and explain why phenol is so much more soluble in water at 25 °C (87 g/L) compared to naphthol (0.74 g/L).

Verified step by step guidance

Phenol (C6H5OH) and naphthol (C10H7OH) are both aromatic compounds with a hydroxyl group (-OH) attached to their benzene rings.

The solubility of a compound in water is influenced by its ability to form hydrogen bonds with water molecules.

Phenol has a single benzene ring, which allows the hydroxyl group to interact more effectively with water, forming hydrogen bonds.

Naphthol, on the other hand, has two fused benzene rings, which makes the molecule bulkier and reduces the accessibility of the hydroxyl group to water molecules, thus limiting hydrogen bonding.

The increased hydrogen bonding capability of phenol compared to naphthol results in its higher solubility in water.

Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Hydrogen Bonding

Hydrogen bonding is a strong type of dipole-dipole interaction that occurs when hydrogen is bonded to highly electronegative atoms like oxygen. In phenol, the hydroxyl (-OH) group can form hydrogen bonds with water molecules, enhancing its solubility. Naphthol, while also containing a hydroxyl group, has a larger hydrophobic aromatic ring that limits its ability to interact with water through hydrogen bonding.

Hydrophobic vs. Hydrophilic Interactions

Hydrophobic interactions refer to the tendency of nonpolar substances to aggregate in aqueous solutions, while hydrophilic interactions involve polar substances that can interact favorably with water. Phenol is more hydrophilic due to its smaller size and ability to form more hydrogen bonds with water, whereas naphthol's larger hydrophobic structure reduces its overall solubility in water.

Molecular Size and Structure

The size and structure of a molecule significantly influence its solubility in water. Phenol has a simpler structure with a smaller molecular size compared to naphthol, which has an additional methyl group that increases its hydrophobic character. This structural difference means that phenol can interact more effectively with water, leading to higher solubility.