JEE Chemistry Aldehydes Ketones and Carboxylic Acids MCQs Set 37

Multiple Choice Questions (MCQs) for JEE Chemistry: Aldehydes Ketones and Carboxylic Acids

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Multiple Choice Questions

Question 1: RCH2OH → RCHO. Which of the following oxidising agents is the most suitable for this reaction?
(a) PCC
(b) K2Cr2O7
(c) KMnO4
(d) All of these
Show Answer & Explanation

Answer: (a) PCC

Explanation:
1. Pyridinium chlorochromate (PCC) in dichloromethane stops at the aldehyde stage.
2. K2Cr2O7 and KMnO4 are strong oxidants and carry the aldehyde on to the carboxylic acid.
3. Answer: (a)

Teacher's Note:
1. Recall the reagent's role: nucleophilic addition-elimination for NH2-type reagents, enolate chemistry for aldol, and the reactivity order acid chloride > anhydride > ester > amide.

Question 2: Which of the following is correct?
(a) CH3COCl > (CH3CO)2O > CH3COOC2H5 > CH3CONH2 (reactivity towards hydrolysis)
(b) C6H5CHO > CH3CHO > CH3COCH3 (reactivity towards cyanohydrin formation)
(c) C6H5OCH3 > C6H5OH > C6H5Cl > C6H5NO2 (reactivity towards electrophilic substitution)
(d) n-Butanol > butan-2-ol > tert-butanol (reactivity towards the Lucas reagent)
Show Answer & Explanation

Answer: (a) CH3COCl > (CH3CO)2O > CH3COOC2H5 > CH3CONH2 (reactivity towards hydrolysis)

Explanation:
1. (a) follows the order of leaving group ability: Cl⁻ > RCOO⁻ > RO⁻ > NH2⁻.
2. (b) is wrong: benzaldehyde is less reactive than acetaldehyde because of resonance with the ring.
3. (c) is wrong: OH activates the ring more than OCH3 in this comparison.
4. (d) is wrong: the Lucas order is 3° > 2° > 1°.
5. Answer: (a)

Teacher's Note:
1. Recall the reagent's role: nucleophilic addition-elimination for NH2-type reagents, enolate chemistry for aldol, and the reactivity order acid chloride > anhydride > ester > amide.

Question 3: Benzaldehyde and acetaldehyde can be distinguished by:
(a) Hinsberg reagent
(b) Tollens' reagent
(c) Baeyer's reagent
(d) Iodoform test
Show Answer & Explanation

Answer: (d) Iodoform test

Explanation:
1. Only acetaldehyde, with its CH3CO– group, gives the yellow precipitate of iodoform.
2. Tollens' reagent and Baeyer's reagent react with both, and Hinsberg's reagent is for amines.
3. Answer: (d)

Teacher's Note:
1. Recall the reagent's role: nucleophilic addition-elimination for NH2-type reagents, enolate chemistry for aldol, and the reactivity order acid chloride > anhydride > ester > amide.

Question 4: The reaction of benzoyl chloride with H2 + Pd/BaSO4 is known as:
(a) Etard reaction
(b) Rosenmund's reduction
(c) Friedel-Crafts reaction
(d) Clemmensen's reduction
Show Answer & Explanation

Answer: (b) Rosenmund's reduction

Explanation:
1. Catalytic hydrogenation of an acid chloride over poisoned Pd/BaSO4 gives the aldehyde (benzaldehyde) and HCl.
2. This is the Rosenmund reduction.
3. Answer: (b)

Teacher's Note:
1. Recall the reagent's role: nucleophilic addition-elimination for NH2-type reagents, enolate chemistry for aldol, and the reactivity order acid chloride > anhydride > ester > amide.

Question 5: Which of the following reactions is not correct according to the major product?
(a) Phthalaldehyde + conc. NaOH → 2-(hydroxymethyl)benzoate
(b) 2-Fluorobutane + alc. KOH, heat → but-2-ene
(c) Anisole + HI → phenol + CH3I
(d) Chloral + NaOH → CHCl3 + HCOONa
Show Answer & Explanation

Answer: (b) 2-Fluorobutane + alc. KOH, heat → but-2-ene

Explanation:
1. (a) is an intramolecular Cannizzaro reaction and (c), (d) are correct.
2. In 2-fluorobutane fluoride is a poor leaving group, so elimination follows the Hofmann rule and gives but-1-ene as the major product.
3. The product but-2-ene is therefore not correct for (b).
4. Answer: (b)

Teacher's Note:
1. Recall the reagent's role: nucleophilic addition-elimination for NH2-type reagents, enolate chemistry for aldol, and the reactivity order acid chloride > anhydride > ester > amide.

Question 6: In which reaction is a racemic mixture obtained as a product?
(a) PhCHO + HCN
(b) (S)-2-Methylbutan-1-ol + SOCl2/pyridine
(c) (R)-2-Chlorobutane + C3H7ONa/ROH, heat
(d) None of these
Show Answer & Explanation

Answer: (a) PhCHO + HCN

Explanation:
1. Cyanide attacks the planar carbonyl carbon from either face with equal probability, giving both enantiomers of the cyanohydrin.
2. In (b) the stereocentre is not touched, and (c) is an SN2 reaction that proceeds with inversion to one enantiomer (with some elimination).
3. Only (a) gives a racemic mixture.
4. Answer: (a)

Teacher's Note:
1. Recall the reagent's role: nucleophilic addition-elimination for NH2-type reagents, enolate chemistry for aldol, and the reactivity order acid chloride > anhydride > ester > amide.

Question 7: Glyoxal (OHC–CHO) on treatment with NaOH gives as the major product:
(a) Ethylene glycol
(b) Sodium oxalate
(c) Sodium glycolate (HOCH2COONa)
(d) HOCH2CHO
Show Answer & Explanation

Answer: (c) Sodium glycolate (HOCH2COONa)

Explanation:
1. Glyoxal has no alpha-hydrogens, and both CHO groups are in one molecule.
2. It undergoes an intramolecular Cannizzaro reaction: one CHO is oxidised to COO⁻ and the other reduced to CH2OH.
3. The product is sodium glycolate.
4. Answer: (c)

Teacher's Note:
1. Recall the reagent's role: nucleophilic addition-elimination for NH2-type reagents, enolate chemistry for aldol, and the reactivity order acid chloride > anhydride > ester > amide.

Question 8: Which of the following does not give the aldol reaction with dil. NaOH?
(a) CH3CHO
(b) CD3CHO
(c) CH3COCH3
(d) PhCHO
Show Answer & Explanation

Answer: (d) PhCHO

Explanation:
1. The aldol reaction needs an alpha-hydrogen (or alpha-deuterium, which is also removed as D⁺).
2. Benzaldehyde has no alpha-hydrogen, so it gives no aldol.
3. Answer: (d)

Teacher's Note:
1. Recall the reagent's role: nucleophilic addition-elimination for NH2-type reagents, enolate chemistry for aldol, and the reactivity order acid chloride > anhydride > ester > amide.

Question 9: Which of the following contains the most acidic hydrogen?
(a) CH3CHO
(b) CH3COCH2COCH3
(c) CH3COCH2COOCH3
(d) CH3COCH3
Show Answer & Explanation

Answer: (b) CH3COCH2COCH3

Explanation:
1. The hydrogens on the CH2 between two C=O groups are acidic because the carbanion is delocalised over two carbonyls.
2. Acetylacetone (pKa about 9) is more acidic than the ester analogue (about 11), because an ester C=O is a weaker acceptor.
3. The simple aldehyde and ketone have pKa about 17–19.
4. Answer: (b)

Teacher's Note:
1. Recall the reagent's role: nucleophilic addition-elimination for NH2-type reagents, enolate chemistry for aldol, and the reactivity order acid chloride > anhydride > ester > amide.

Question 10: CH3CHO can react with:
(a) NH2–NH2
(b) NH2–NH–CO–NH2
(c) Ph–NH–NH2
(d) All of these
Show Answer & Explanation

Answer: (d) All of these

Explanation:
1. Acetaldehyde undergoes nucleophilic addition-elimination with ammonia derivatives.
2. With hydrazine it gives a hydrazone, with semicarbazide a semicarbazone, and with phenylhydrazine a phenylhydrazone.
3. Answer: (d)

Teacher's Note:
1. Recall the reagent's role: nucleophilic addition-elimination for NH2-type reagents, enolate chemistry for aldol, and the reactivity order acid chloride > anhydride > ester > amide.

Question 11: Which gives an aldehyde on hydration by H2SO4 and HgSO4?
(a) Propyne
(b) Pent-2-yne
(c) Phenylacetylene
(d) Ethyne
Show Answer & Explanation

Answer: (d) Ethyne

Explanation:
1. Markovnikov hydration of a terminal alkyne gives a ketone, and of an internal alkyne a ketone (or ketone mixture).
2. Only ethyne gives an aldehyde (acetaldehyde), because its hydration product, vinyl alcohol, tautomerises to CH3CHO.
3. Answer: (d)

Teacher's Note:
1. Recall the reagent's role: nucleophilic addition-elimination for NH2-type reagents, enolate chemistry for aldol, and the reactivity order acid chloride > anhydride > ester > amide.

Question 12: CH3–CH=CH–CH2–CH2–CN is treated with (1) DIBAL-H and (2) H2O. The product is:
(a) CH3(CH2)4CN
(b) CH3(CH2)5NH2
(c) CH3–CH=CH–CH2–CH2–CHO
(d) CH3(CH2)3CH2CHO
Show Answer & Explanation

Answer: (c) CH3–CH=CH–CH2–CH2–CHO

Explanation:
1. DIBAL-H reduces a nitrile to an imine, which hydrolyses to an aldehyde.
2. It does not reduce an isolated C=C bond.
3. The product is hex-4-enal.
4. Answer: (c)

Teacher's Note:
1. Recall the reagent's role: nucleophilic addition-elimination for NH2-type reagents, enolate chemistry for aldol, and the reactivity order acid chloride > anhydride > ester > amide.

Question 13: In which reaction is ethyl phenyl ketone obtained?
(a) C6H5CN + EtMgBr, then H3O⁺
(b) CH3CH2COCl + Ph2Cd
(c) Benzene + CH3CH2COCl, anhydrous AlCl3
(d) All of them
Show Answer & Explanation

Answer: (d) All of them

Explanation:
1. Ethyl phenyl ketone is propiophenone, C6H5COCH2CH3.
2. A Grignard reagent adds to a nitrile to give a ketone after hydrolysis, a diaryl cadmium reagent converts an acid chloride to a ketone, and Friedel-Crafts acylation gives the ketone.
3. All three routes give it.
4. Answer: (d)

Teacher's Note:
1. Recall the reagent's role: nucleophilic addition-elimination for NH2-type reagents, enolate chemistry for aldol, and the reactivity order acid chloride > anhydride > ester > amide.

Question 14: Ph–CO–CH3 + NaOCl gives A + a salt, and A + CH3COCH3 gives B. B is:
(a)
(b)
(c)
Show Answer & Explanation

Answer: (a)

Explanation:
1. NaOCl brings about the haloform reaction: acetophenone gives chloroform (A) and sodium benzoate (the salt).
2. Chloroform adds to acetone (base catalysed) to give chlorobutanol (chloretone), (CH3)2C(OH)CCl3.
3. Answer: (a)

Teacher's Note:
1. Recall the reagent's role: nucleophilic addition-elimination for NH2-type reagents, enolate chemistry for aldol, and the reactivity order acid chloride > anhydride > ester > amide.

Question 15: CH3CH=CH–CO–CH3 + NH2OH/H⁺ gives as the major product:
(a) CH3CH(NH2)CH(OH)COCH3
(b) CH3CH(OH)CH(NH2)COCH3
(c) CH3CH=CH–C(CH3)=NOH
(d) CH3CH(OH)CH2COCH3
Show Answer & Explanation

Answer: (c) CH3CH=CH–C(CH3)=NOH

Explanation:
1. Hydroxylamine attacks the C=O group (1,2-addition) and loses water to give an oxime.
2. The C=C bond is untouched under acidic conditions.
3. The product is the ketoxime CH3CH=CH–C(CH3)=NOH.
4. Answer: (c)

Teacher's Note:
1. Recall the reagent's role: nucleophilic addition-elimination for NH2-type reagents, enolate chemistry for aldol, and the reactivity order acid chloride > anhydride > ester > amide.

Question 16: Phthalic acid + NH3 (strong heating) gives A. A is:
(a) Phthalamide
(b) 2-Carbamoylbenzoic acid
(c) Phthalimide
(d) Phthalic anhydride
Show Answer & Explanation

Answer: (c) Phthalimide

Explanation:
1. Phthalic acid and ammonia first form the ammonium salt.
2. Strong heating then removes two molecules of water to give the cyclic imide, phthalimide.
3. Answer: (c)

Teacher's Note:
1. Recall the reagent's role: nucleophilic addition-elimination for NH2-type reagents, enolate chemistry for aldol, and the reactivity order acid chloride > anhydride > ester > amide.

Question 17: CH3CH2COOH + Cl2/red P gives A, A with NaOH/CaO (heat) gives B, and B with alc. KOH (heat) gives C. C is:
(a) CH3CH(OH)CH3
(b) CH3CH=CH2
(c) CH3CH2COOR
(d) CH2=CH2
Show Answer & Explanation

Answer: (d) CH2=CH2

Explanation:
1. HVZ reaction gives 2-chloropropanoic acid (A).
2. Soda lime decarboxylates it to chloroethane, CH3CH2Cl (B).
3. Alcoholic KOH removes HCl to give ethene (C).
4. Answer: (d)

Teacher's Note:
1. Recall the reagent's role: nucleophilic addition-elimination for NH2-type reagents, enolate chemistry for aldol, and the reactivity order acid chloride > anhydride > ester > amide.

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