Question

An organic compound with the molecular formula \(\text{C}_7\text{H}_8\text{O}\) is completely insoluble in water but dissolves readily in an aqueous \(\text{NaOH}\) solution. When treated with bromine water, it forms a white precipitate. Identify the compound.

• A. Benzyl alcohol
• B. Anisole
• C. $o$-Cresol
• D. Methoxybenzene

Hint:

Organic molecules that dissolve cleanly in aqueous \(\text{NaOH}\) but fail to react or evolve gas in weaker \(\text{NaHCO}_3\) contain a phenolic hydroxyl group.

Answer 1

The Correct Option is C

Concept: We can determine structural properties based on characteristic solubility trends:
• Phenols are acidic enough to react with strong bases like \(\text{NaOH}\), forming water-soluble sodium phenoxide salts. Alcohols and ethers do not react.
• The strongly activating hydroxyl group on the ring drives extremely rapid electrophilic substitution reactions.

Step 1: Narrow down functional classes based on basic solubility.
The formula \(\text{C}_7\text{H}_8\text{O}\) matches structural isomers like benzyl alcohol, anisole, and cresols. Because this compound reacts and dissolves in \(\text{NaOH}\), it must be a phenol variant ($o$-cresol).

Step 2: Verify electrophilic addition behavior.
Treating $o$-cresol with bromine water causes rapid ring bromination at available ortho and para positions, generating a characteristic halogenated white precipitate.