9 NEET UG practice questions on Phenols, part of Chemistry. Below are 9 of them in full, each with the answer and a written explanation.
Answer: Salicylaldehyde
When phenol is treated with chloroform (CHCl3) and aqueous sodium hydroxide, the Reimer–Tiemann reaction occurs, yielding salicylaldehyde (o-hydroxybenzaldehyde) as the major product. Salicylic acid is obtained via Kolbe's reaction, phenolphthalein by condensation with phthalic anhydride, and benzaldehyde from toluene oxidation.
Answer: o- and p-nitrophenol
The −OH group is strongly activating and ortho-para directing. With dilute HNO3, electrophilic substitution occurs mainly at ortho and para positions, yielding a mixture of o- and p-nitrophenol. m-Nitrophenol is a minor product; trinitrophenol requires concentrated acids; nitrobenzene results from benzene nitration.
Answer: p-Benzoquinone
Oxidation of phenol with a strong oxidizing agent like chromic acid converts the hydroxyl group into a carbonyl group, yielding p-benzoquinone. Benzene is a reduction product, benzoic acid comes from oxidation of toluene, and catechol is a dihydroxybenzene formed by hydroxylation, not direct oxidation of phenol.
Answer: Cumene hydroperoxide
In the cumene process, cumene (isopropylbenzene) is oxidized to cumene hydroperoxide, which on acid-catalyzed cleavage yields phenol and acetone. Benzoic acid is from toluene oxidation, chlorobenzene is a starting material for other phenol syntheses, and aniline is from nitrobenzene reduction.
Answer: p-Nitrophenol
The nitro group is strongly electron-withdrawing, stabilising the phenoxide ion through resonance and inductive effects, thereby increasing acidity. Methyl and methoxy groups are electron-donating, which reduce acidity. Hence, p-nitrophenol is the strongest acid among the given options.
Answer: Formation of salicylic acid
In Kolbe's reaction, sodium phenoxide is treated with carbon dioxide under pressure followed by acidification to give salicylic acid (o-hydroxybenzoic acid). Benzaldehyde is produced by Reimer–Tiemann reaction, phenyl acetate by acetylation, and aniline by reduction of nitrobenzene.
Answer: Phenol forms intermolecular hydrogen bonds
Phenol possesses a hydroxyl group that can form strong intermolecular hydrogen bonds, requiring more energy to break, resulting in a higher boiling point. While phenol has a slightly higher molecular weight, the primary factor is hydrogen bonding.
Answer: Formation of a coordination compound
Phenol reacts with FeCl3 to form a violet-coloured complex, a coordination compound where Fe3+ binds with oxygen atoms of phenoxide ions. This is a characteristic test for phenols. The colour is not due to oxidation, reduction, or dye formation.
Answer: Phenoxide ion is stabilized by resonance
The phenoxide ion (C6H5O−) is resonance-stabilized because the negative charge can be delocalized into the aromatic ring. In contrast, the ethoxide ion (C2H5O−) lacks such resonance stabilization, making phenol a stronger acid than ethanol.
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