JEE Chemistry Alcohols Phenols and Ethers MCQs Set 22

Answer: (a) Glycol

Explanation:
1. Ethylene glycol lowers the freezing point of water in car radiators.

Teacher's Note:
1. Methanol is poisonous; denatured spirit is ethanol made unfit to drink.
2. Link every compound with its use: ethanol in tonics and power alcohol, glycerol in nitroglycerine, glycol as antifreeze, ether as anaesthetic.

Answer: (c) 2 and 4

Explanation:
1. Friedel-Crafts alkylation fails on rings deactivated by strong electron-withdrawing groups (nitro, carboxyl), so only styrene and phenol react.

Teacher's Note:
1. Nitro groups at ortho and para positions increase the acidity of phenol, and ortho-nitrophenol is steam volatile.
2. Draw the structures and decide which functional group controls the reaction before reading the options.

Answer: (c) \( \ce{R-CH2-CH2-OH} \)

Explanation:
1. The Grignard carbon attacks the less hindered ring carbon, giving a primary alcohol with two more carbons.

Teacher's Note:
1. Grignard reagents add to carbonyl groups and are destroyed by water, alcohols and acids.
2. In ether cleavage by HI or HBr, the alkyl-oxygen bond breaks; aryl-oxygen bonds do not.

Answer: (c) Vacuum distillation

Explanation:
1. Reduced pressure lowers the boiling point so glycerol distils without decomposing.

Teacher's Note:
1. Glycerol is propane-1,2,3-triol; it gives nitroglycerine, allyl iodide with HI, and acrolein on dehydration.
2. Draw the structures and decide which functional group controls the reaction before reading the options.

Answer: (a) 1° > 2° > 3°

Explanation:
1. Branching reduces surface area and van der Waals forces, so boiling points fall from primary to tertiary.

Teacher's Note:
1. Draw the structures and decide which functional group controls the reaction before reading the options.
2. In ether cleavage by HI or HBr, the alkyl-oxygen bond breaks; aryl-oxygen bonds do not.

Answer: (c) Methyl iodide + phenol

Explanation:
1. The alkyl-oxygen bond is cleaved: \( \ce{C6H5OCH3 + HI -> C6H5OH + CH3I} \).

Teacher's Note:
1. In ether cleavage by HI or HBr, the alkyl-oxygen bond breaks; aryl-oxygen bonds do not.
2. Draw the structures and decide which functional group controls the reaction before reading the options.

Answer: (c) Ethylene glycol

Explanation:
1. Cold alkaline \( \ce{KMnO4} \) hydroxylates the double bond (syn): ethane-1,2-diol.

Teacher's Note:
1. Draw the structures and decide which functional group controls the reaction before reading the options.
2. In ether cleavage by HI or HBr, the alkyl-oxygen bond breaks; aryl-oxygen bonds do not.

Answer: (c) Tertiary > primary

Explanation:
1. Ease of dehydration follows carbocation stability: 3° > 2° > 1°.

Teacher's Note:
1. Dehydration of alcohols follows carbocation stability, so tertiary alcohols dehydrate fastest; ethanol gives ether at 413 K and ethene at 443 K.
2. In ether cleavage by HI or HBr, the alkyl-oxygen bond breaks; aryl-oxygen bonds do not.

Answer: (c) \( \ce{B2H6} \) followed by \( \ce{H2O2} \)

Explanation:
1. Hydroboration-oxidation gives anti-Markovnikov hydration; the other methods give propan-2-ol.

Teacher's Note:
1. In ether cleavage by HI or HBr, the alkyl-oxygen bond breaks; aryl-oxygen bonds do not.
2. Draw the structures and decide which functional group controls the reaction before reading the options.

Answer: (d) All of these

Explanation:
1. All three methods give different results for the three classes.

Teacher's Note:
1. Draw the structures and decide which functional group controls the reaction before reading the options.
2. In ether cleavage by HI or HBr, the alkyl-oxygen bond breaks; aryl-oxygen bonds do not.

Answer: (b) Benzene

Explanation:
1. Vapour-phase oxidation of benzene gives phenol (and maleic anhydride at higher conversion).

Teacher's Note:
1. In ether cleavage by HI or HBr, the alkyl-oxygen bond breaks; aryl-oxygen bonds do not.
2. Draw the structures and decide which functional group controls the reaction before reading the options.

Answer: (b) \( \ce{C6H5COOH} \)

Explanation:
1. Chlorobenzene (Dow), diazonium chloride (hydrolysis) and sodium benzenesulphonate (alkali fusion) all give phenol or phenoxide; benzoic acid does not.

Teacher's Note:
1. Diazonium salts give phenol on warming with water and azo dyes by coupling with phenols and amines.
2. Draw the structures and decide which functional group controls the reaction before reading the options.

Answer: (a) \( \ce{C2H5-O-CH(CH3)-O-OH} \)

Explanation:
1. Auto-oxidation at the alpha carbon of diethyl ether gives its hydroperoxide.

Teacher's Note:
1. Ethers are cleaved by HI, form explosive peroxides in air, and act as Lewis bases forming etherates.
2. In ether cleavage by HI or HBr, the alkyl-oxygen bond breaks; aryl-oxygen bonds do not.

Answer: (d) \( \ce{CH3OC2H5} \), \( \ce{CH3OCH3} \) and \( \ce{C2H5OC2H5} \)

Explanation:
1. Random bimolecular dehydration gives the mixed ether and both symmetrical ethers.

Teacher's Note:
1. Dehydration of alcohols follows carbocation stability, so tertiary alcohols dehydrate fastest; ethanol gives ether at 413 K and ethene at 443 K.
2. Draw the structures and decide which functional group controls the reaction before reading the options.

Answer: (b) IV > III > I > II

Explanation:
1. Leaving ability follows the stability of the anion: triflate > mesylate > acetate > methoxide.

Teacher's Note:
1. In ether cleavage by HI or HBr, the alkyl-oxygen bond breaks; aryl-oxygen bonds do not.
2. Draw the structures and decide which functional group controls the reaction before reading the options.

Answer: (a) Cyclic ethers

Explanation:
1. An epoxide is a three-membered cyclic ether.

Teacher's Note:
1. Ethers are cleaved by HI, form explosive peroxides in air, and act as Lewis bases forming etherates.
2. Draw the structures and decide which functional group controls the reaction before reading the options.

Answer: (b) 1-Bromo-1-(4-hydroxyphenyl)propane

Explanation:
1. HBr adds to the side-chain C=C by Markovnikov addition through the benzylic carbocation; the ring OH is unaffected.

Teacher's Note:
1. In ether cleavage by HI or HBr, the alkyl-oxygen bond breaks; aryl-oxygen bonds do not.
2. Draw the structures and decide which functional group controls the reaction before reading the options.

Answer: (c) Anisole

Explanation:
1. Benzyl alcohol, acetophenone and toluene all have an oxidisable benzylic carbon that becomes COOH. In anisole the OCH3 group cannot be converted to COOH, so no benzoic acid forms.

Teacher's Note:
1. Draw the structures and decide which functional group controls the reaction before reading the options.
2. In ether cleavage by HI or HBr, the alkyl-oxygen bond breaks; aryl-oxygen bonds do not.

Answer: (c) A is true, but R is false.

Explanation:
1. Saponification gives sodium palmitate (soap), so the assertion is true.
2. Glycerol is a viscous liquid, so the reason is false.

Teacher's Note:
1. Glycerol is propane-1,2,3-triol; it gives nitroglycerine, allyl iodide with HI, and acrolein on dehydration.
2. Test statements about acidity or dehydration with the stability of the intermediate ion or carbocation.

Answer: (a) Both A and R are true, and R is the correct explanation of A.

Explanation:
1. The OH group donates its lone pair, giving an additional resonance structure with oxygen carrying the positive charge.
2. This extra stabilisation explains the higher reactivity.

Teacher's Note:
1. Decide separately whether the assertion and reason are true, then ask whether the reason really explains the assertion.
2. Test statements about acidity or dehydration with the stability of the intermediate ion or carbocation.

Answer: (c) A is true, but R is false.

Explanation:
1. Phenoxide has an electron-rich ring that attacks CO2, so the assertion is true.
2. Ethoxide is the stronger base because phenoxide's charge is delocalised, so the reason is false.

Teacher's Note:
1. Kolbe-Schmidt reaction: sodium phenoxide with CO2 under pressure gives salicylic acid after acidification.
2. Test statements about acidity or dehydration with the stability of the intermediate ion or carbocation.

Answer: (c) A is true, but R is false.

Explanation:
1. The reagent composition is correct.
2. Primary alcohols give no turbidity at room temperature, so the reason is false.

Teacher's Note:
1. In the Lucas test turbidity appears at once for tertiary, in about 5 minutes for secondary, and only on heating for primary alcohols.
2. Decide separately whether the assertion and reason are true, then ask whether the reason really explains the assertion.

Answer: (a) Both A and R are true, and R is the correct explanation of A.

Explanation:
1. Phenolic OH groups form coloured complexes with Fe(III); resorcinol has two such groups, so the reason explains the assertion.

Teacher's Note:
1. Test statements about acidity or dehydration with the stability of the intermediate ion or carbocation.
2. Decide separately whether the assertion and reason are true, then ask whether the reason really explains the assertion.

Answer: (b) Both A and R are true, but R is not the correct explanation of A.

Explanation:
1. Reduced pressure lowers the boiling point and avoids decomposition at 563 K, so the assertion is true.
2. The reason is also true but does not explain why vacuum is needed.

Teacher's Note:
1. Decide separately whether the assertion and reason are true, then ask whether the reason really explains the assertion.
2. Test statements about acidity or dehydration with the stability of the intermediate ion or carbocation.

Answer: (a) Both A and R are true, and R is the correct explanation of A.

Explanation:
1. Phenol dissolves in NaOH to form sodium phenoxide, while an alcohol does not; the difference in acidity explains the test.

Teacher's Note:
1. Acidity order: carboxylic acids > carbonic acid > phenol > water > alcohols; nitro groups increase and alkyl groups decrease the acidity of phenols.
2. Test statements about acidity or dehydration with the stability of the intermediate ion or carbocation.

Answer: (b) Both A and R are true, but R is not the correct explanation of A.

Explanation:
1. Zeolite catalysts such as ZSM-5 convert methanol to hydrocarbons, so the assertion is true.
2. The reason is true but pore structure is only part of the explanation (acid sites matter).

Teacher's Note:
1. Acidity order: carboxylic acids > carbonic acid > phenol > water > alcohols; nitro groups increase and alkyl groups decrease the acidity of phenols.
2. Decide separately whether the assertion and reason are true, then ask whether the reason really explains the assertion.

Answer: (a) Both A and R are true, and R is the correct explanation of A.

Explanation:
1. Cleavage proceeds through the more stable benzyl carbocation (SN1), giving benzyl iodide and methanol.

Teacher's Note:
1. Test statements about acidity or dehydration with the stability of the intermediate ion or carbocation.
2. Decide separately whether the assertion and reason are true, then ask whether the reason really explains the assertion.

Answer: (c) A is true, but R is false.

Explanation:
1. Acetic acid (pKa 4.76) is more acidic than phenol (10)
2. The reason is false: in acetate the charge is shared equally by two electronegative oxygens, which is better stabilisation than in phenoxide.

Teacher's Note:
1. Acidity order: carboxylic acids > carbonic acid > phenol > water > alcohols; nitro groups increase and alkyl groups decrease the acidity of phenols.
2. Decide separately whether the assertion and reason are true, then ask whether the reason really explains the assertion.