JEE Chemistry Alcohols Phenols and Ethers MCQs Set 32

Answer: (c) CH₃CH₂C(CH₃)(OH)CH₂CH₃

Explanation:
1. Acid dehydration goes through a carbocation, so tertiary alcohols dehydrate most easily (3° > 2° > 1°).
2. Option (c), 3-methylpentan-3-ol, is the only tertiary alcohol.
3. Answer: (c)

Teacher's Note:
1. Link each reagent to the functional group it acts on, and remember the key named reactions of alcohols, phenols and ethers.

Answer: (c) 2,4,6-Tribromophenol

Explanation:
1. The OH group strongly activates the ring at the ortho and para positions.
2. In water, phenol is partly ionised and reacts so fast that all three positions are brominated, giving a white precipitate of 2,4,6-tribromophenol.
3. Answer: (c)

Teacher's Note:
1. Link each reagent to the functional group it acts on, and remember the key named reactions of alcohols, phenols and ethers.

Answer: (c) CH₃–CH=CH–CHO

Explanation:
1. PCC is a mild oxidant that stops at the aldehyde stage.
2. It oxidises the primary alcohol group to CHO and does not touch the C=C bond.
3. The product is but-2-enal.
4. Answer: (c)

Teacher's Note:
1. Link each reagent to the functional group it acts on, and remember the key named reactions of alcohols, phenols and ethers.

Answer: (b) o- and p-Nitrophenol

Explanation:
1. The OH group directs the electrophile to the ortho and para positions.
2. Dilute nitric acid gives a mixture of o-nitrophenol and p-nitrophenol; concentrated nitric acid would give picric acid.
3. Answer: (b)

Teacher's Note:
1. Link each reagent to the functional group it acts on, and remember the key named reactions of alcohols, phenols and ethers.

Answer: (a) 4-Hydroxybenzenesulphonic acid

Explanation:
1. Sulphonation of phenol is temperature dependent.
2. At low temperature the ortho product is formed (kinetic control).
3. At 100°C the more stable para isomer is the major product (thermodynamic control).
4. Answer: (a)

Teacher's Note:
1. Link each reagent to the functional group it acts on, and remember the key named reactions of alcohols, phenols and ethers.

Answer: (b) Iodoform test

Explanation:
1. Ethanol has a CH₃CH(OH)– group and gives yellow iodoform with I₂/NaOH.
2. Methanol does not.
3. HCl, the Lucas reagent and sodium react similarly with both (or not at all).
4. Answer: (b)

Teacher's Note:
1. Link each reagent to the functional group it acts on, and remember the key named reactions of alcohols, phenols and ethers.

Answer: (d) All of the above

Explanation:
1. Williamson synthesis: sodium ethoxide with ethyl iodide gives diethyl ether.
2. Ethanol heated with conc. H₂SO₄ at 140°C gives diethyl ether by dehydration.
3. Dry Ag₂O with an alkyl halide also gives ether.
4. All three are correct.
5. Answer: (d)

Teacher's Note:
1. Link each reagent to the functional group it acts on, and remember the key named reactions of alcohols, phenols and ethers.

Answer: (b) 95.6% C₂H₅OH

Explanation:
1. Fractional distillation of fermented liquor gives an azeotrope with about 95.6% ethanol and 4.4% water by mass.
2. This is rectified spirit.
3. Answer: (b)

Teacher's Note:
1. Link each reagent to the functional group it acts on, and remember the key named reactions of alcohols, phenols and ethers.

Answer: (d) Triphenyl phosphate

Explanation:
1. The C–OH bond of phenol is hard to break because of resonance.
2. PCl₅ reacts at the O–H bond instead and gives mainly triphenyl phosphate, with chlorobenzene as only a minor product.
3. Answer: (d)

Teacher's Note:
1. Link each reagent to the functional group it acts on, and remember the key named reactions of alcohols, phenols and ethers.

Answer: (b) Phenol and phthalic anhydride

Explanation:
1. Two molecules of phenol condense with phthalic anhydride in the presence of conc. H₂SO₄ to give phenolphthalein.
2. Answer: (b)

Teacher's Note:
1. Link each reagent to the functional group it acts on, and remember the key named reactions of alcohols, phenols and ethers.

Answer: (c) m-Chlorophenol

Explanation:
1. Phenols are more acidic than alcohols because the phenoxide ion is stabilised by resonance.
2. m-Chlorophenol is more acidic than phenol because the –I effect of Cl stabilises the phenoxide ion further.
3. Answer: (c)

Teacher's Note:
1. Link each reagent to the functional group it acts on, and remember the key named reactions of alcohols, phenols and ethers.

Answer: (c) CH₃CONH₂ + LiAlH₄

Explanation:
1. Diazotisation of a primary aliphatic amine gives the alcohol (a); acetaldehyde with a Grignard reagent gives propan-2-ol (b); ethyl chloride with aq. KOH gives ethanol (d).
2. LiAlH₄ reduces an amide to an amine (ethylamine), not to an alcohol.
3. Answer: (c)

Teacher's Note:
1. Link each reagent to the functional group it acts on, and remember the key named reactions of alcohols, phenols and ethers.

Answer: (b) +

Explanation:
1. HI cleaves the bond between oxygen and the alkyl (benzyl) group, because the aryl C–O bond is stronger.
2. The benzyl carbon forms a stable benzylic cation, so the reaction is fast.
3. The products are benzyl iodide and phenol.
4. Answer: (b)

Teacher's Note:
1. Link each reagent to the functional group it acts on, and remember the key named reactions of alcohols, phenols and ethers.