When benzoyl chloride is treated with H2 in the presence of Pd-BaSO4, benzaldehyde is formed. This reaction is called

This is the Rosenmund reduction.Acid chlorides are reduced to aldehydes by hydrogen over palladium on barium sulphate. The BaSO4 (often with a little quinoline or sulphur) partly poisons the catalyst, so the reduction stops at the aldehyde instead of going on to the alcohol: C6H5COCl + H2 → C6H5CHO + HCl.Clemmensen (zinc amalgam and HCl) and Wolff-Kishner (hydrazine and base) reductions convert a carbonyl group to CH2. The Cannizzaro reaction is the disproportionation of an aldehyde without alpha-hydrogens, and the Williamson reaction makes ethers.

Benzaldehyde reacts with HNO3/H2SO4 at 273-283 K to give

The product is m-nitrobenzaldehyde.The -CHO group withdraws electrons from the ring and is a meta director. Under the mild nitrating conditions (273-283 K) the aldehyde group is not oxidised, so nitration simply puts a -NO2 group at the meta position.Ortho products are not favoured by a meta-directing group, and the benzoic acid options would need the -CHO group to be oxidised, which these conditions do not do.

Aldehydes and Ketones Questions and Answers

Q: When C6H5CHO reacts with the mixture of HNO3 and H2SO4 at 273-283K gives

The product is m-Nitrobenzaldehyde.The aldehyde group withdraws electrons from the ring by resonance, deactivating it and directing an incoming electrophile to the meta position. Nitration with \(HNO_{3}/H_{2}SO_{4}\) at 273-283 K therefore gives 3-nitrobenzaldehyde.Ortho and para products dominate only with activating groups such as -OH or \(-CH_{3}\). Toluene and nitrobenzene would need removal of the CHO group, which nitration does not do.

Q: The aldehyde that does not respond to Fehling's test is

The aldehyde that does not respond to Fehling's test is phenylmethanal (benzaldehyde).Fehling's solution contains Cu2+ in alkaline tartrate. Aliphatic aldehydes reduce it to a red precipitate of Cu2O. Aromatic aldehydes such as benzaldehyde do not give this test, although they do reduce Tollens' reagent.Methanal, ethanal, propanal and butanal are all aliphatic aldehydes and give the red precipitate, so they are not the answer.

Q: Clemmensen reduction involves the formation of an alkane from a ketone on treatment with

Clemmensen reduction uses Zn amalgam and concentrated HCl.Heating an aldehyde or ketone with zinc amalgam and concentrated hydrochloric acid reduces the C=O group to CH2, giving the alkane: for example propanone gives propane.Hydrazine followed by heating with KOH in glycol is the Wolff-Kishner reduction, which achieves the same change under basic conditions. LiAlH4 and H2/Ni reduce ketones only to secondary alcohols, and H2 with Pd/BaSO4 is the Rosenmund catalyst for reducing acid chlorides to aldehydes.

Q: Which of the following undergoes haloform reaction?

The compound that gives the haloform reaction is propanone.The haloform reaction is given by methyl ketones and other compounds with a CH3CO- group (or CH3CH(OH)- that is oxidised to it). Propanone, CH3COCH3, has this group and gives iodoform with iodine and alkali.Benzophenone, methanal, propanal (CH3CH2CHO) and 2,2-dimethylpropanal have no CH3CO- group, so none of them gives the test. Ethanal is the only aldehyde that does.

Q: An organic compound with molecular formula,C5H10O, does not reduce Tollen's reagent but forms an addition compound with sodium hydrogen sulphite and gives positive iodoform test. On vigorous oxidation, it gives ethanoic and propanoic acids. The compound is

The compound is pentan-2-one.Each clue narrows it down. C5H10O with no Tollens' reaction is a ketone, not an aldehyde, so pentanal is out. Forming a bisulphite adduct and giving the iodoform test both point to a methyl ketone, CH3CO-R.Pentan-2-one, CH3COCH2CH2CH3, fits, and vigorous oxidation cleaves it beside the carbonyl to give ethanoic acid and propanoic acid.Pentan-3-one has no CH3CO group and fails the iodoform test. Ethoxyethane and pentanol are not carbonyl compounds (and ethoxyethane is C4H10O).

Q: In aldol condensation reaction, 1, 3-diphenylprop-2-en-1--one is obtained as major product in the reaction between

The reactants are benzaldehyde and acetophenone.1,3-Diphenylprop-2-en-1-one is C6H5CO-CH=CH-C6H5 (chalcone). It forms by a crossed aldol (Claisen-Schmidt) condensation: the enolate of acetophenone, C6H5COCH3, adds to benzaldehyde, which has no alpha-hydrogen, and the product loses water to give the conjugated enone.Benzophenone has no alpha-hydrogens, so with benzaldehyde neither partner can form an enolate. Propan-2-one or butan-2-one with benzaldehyde give products with methyl or ethyl groups, not a second phenyl ring, and acetophenone with propan-2-one gives no benzylidene unit.

Q: Which of the following is a commercial method of manufacture of benzaldehyde?

The commercial method is side chain chlorination of toluene followed by hydrolysis.Chlorinating toluene in the side chain gives benzal chloride, C6H5CHCl2, which is hydrolysed to benzaldehyde. This is the method used industrially.The other routes are laboratory methods: the Rosenmund reduction of benzoyl chloride, the Etard reaction with chromyl chloride, oxidation with chromic oxide in acetic anhydride (CrO3, though the option prints Cr2O3), and the Gattermann-Koch reaction with CO and HCl.

Q: Which is the reagent used for the following conversion?

The reagent is [Ag(NH3)2]+, Tollens' reagent.The conversion oxidises the aldehyde group to a carboxylate while leaving the ring ketone untouched. Tollens' reagent is a mild oxidising agent that oxidises aldehydes to carboxylate ions (and deposits a silver mirror) but does not attack ketones, so it is selective.NaBH4 reduces carbonyl groups; NaCN/HCl adds HCN to them; SOCl2 converts acids or alcohols to chlorides; and ozonolysis cleaves C=C double bonds. None oxidises CHO to COO-.

31.

When C₆H₅CHO reacts with the mixture of HNO₃ and H₂SO₄ at 273-283K gives

A.o- Nitrobenzaldehyde
B.m-Nitrobenzaldehyde
C.p-Nitrobenzaldehyde
D.Toluene
E.Nitrobenzene

Exam Year(s)

KEAM - 2025,

Answer: B

The product is m-Nitrobenzaldehyde.

The aldehyde group withdraws electrons from the ring by resonance, deactivating it and directing an incoming electrophile to the meta position. Nitration with \(HNO_{3}/H_{2}SO_{4}\) at 273-283 K therefore gives 3-nitrobenzaldehyde.

Ortho and para products dominate only with activating groups such as -OH or \(-CH_{3}\). Toluene and nitrobenzene would need removal of the CHO group, which nitration does not do.

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32.

When benzoyl chloride is treated with H₂ in the presence of Pd-BaSO₄, benzaldehyde is formed. This reaction is called

A.Clemmensen reduction
B.Wolff-Kischner reduction
C.Rosenmund reduction
D.Cannizaro reaction
E.Williamson reaction

Exam Year(s)

KEAM - 2026,

Answer: C

This is the Rosenmund reduction.

Acid chlorides are reduced to aldehydes by hydrogen over palladium on barium sulphate. The BaSO₄ (often with a little quinoline or sulphur) partly poisons the catalyst, so the reduction stops at the aldehyde instead of going on to the alcohol: C₆H₅COCl + H₂ → C₆H₅CHO + HCl.

Clemmensen (zinc amalgam and HCl) and Wolff-Kishner (hydrazine and base) reductions convert a carbonyl group to CH₂. The Cannizzaro reaction is the disproportionation of an aldehyde without alpha-hydrogens, and the Williamson reaction makes ethers.

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33.

The aldehyde that does not respond to Fehling's test is

A.methanal
B.ethanal
C.propanal
D.butanal
E.phenylmethanal

Exam Year(s)

KEAM - 2026,

Answer: E

The aldehyde that does not respond to Fehling's test is phenylmethanal (benzaldehyde).

Fehling's solution contains Cu²⁺ in alkaline tartrate. Aliphatic aldehydes reduce it to a red precipitate of Cu₂O. Aromatic aldehydes such as benzaldehyde do not give this test, although they do reduce Tollens' reagent.

Methanal, ethanal, propanal and butanal are all aliphatic aldehydes and give the red precipitate, so they are not the answer.

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34.

Clemmensen reduction involves the formation of an alkane from a ketone on treatment with

A.\(\text{H}_{2}\) in the presence of Ni catalyst
B.Zn amalgam and concentrated HCl
C.\(\text{LiAlH}_{4}\)
D.\(\text{N}_{2}\text{H}_{4}\) followed by heating with KOH in glycol
E.\(\text{H}_{2}\) in the presence of Pd/BaSO4

Exam Year(s)

KEAM - 2026,

Answer: B

Clemmensen reduction uses Zn amalgam and concentrated HCl.

Heating an aldehyde or ketone with zinc amalgam and concentrated hydrochloric acid reduces the C=O group to CH₂, giving the alkane: for example propanone gives propane.

Hydrazine followed by heating with KOH in glycol is the Wolff-Kishner reduction, which achieves the same change under basic conditions. LiAlH₄ and H₂/Ni reduce ketones only to secondary alcohols, and H₂ with Pd/BaSO₄ is the Rosenmund catalyst for reducing acid chlorides to aldehydes.

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35.

Which of the following undergoes haloform reaction?

A.Benzophenone
B.2, 2-Dimethylpropanal
C.Methanal
D.Propanone
E.Propanal

Exam Year(s)

KEAM - 2026,

Answer: D

The compound that gives the haloform reaction is propanone.

The haloform reaction is given by methyl ketones and other compounds with a CH₃CO- group (or CH₃CH(OH)- that is oxidised to it). Propanone, CH₃COCH₃, has this group and gives iodoform with iodine and alkali.

Benzophenone, methanal, propanal (CH₃CH₂CHO) and 2,2-dimethylpropanal have no CH₃CO- group, so none of them gives the test. Ethanal is the only aldehyde that does.

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36.

Benzaldehyde reacts with HNO₃/H₂SO₄ at 273-283 K to give

A.benzoic acid
B.m-nitrobenzoic acid
C.m-nitrobenzaldehyde
D.o-nitrobenzaldehyde
E.o-nitrobenzoic acid

Exam Year(s)

KEAM - 2026,

Answer: C

The product is m-nitrobenzaldehyde.

The -CHO group withdraws electrons from the ring and is a meta director. Under the mild nitrating conditions (273-283 K) the aldehyde group is not oxidised, so nitration simply puts a -NO₂ group at the meta position.

Ortho products are not favoured by a meta-directing group, and the benzoic acid options would need the -CHO group to be oxidised, which these conditions do not do.

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37.

An organic compound with molecular formula,C₅H₁₀O, does not reduce Tollen's reagent but forms an addition compound with sodium hydrogen sulphite and gives positive iodoform test. On vigorous oxidation, it gives ethanoic and propanoic acids. The compound is

A.pentan-3-one
B.pentanal
C.pentan-2-one
D.ethoxy ethane
E.pentanol

Exam Year(s)

KEAM - 2026,

Answer: C

The compound is pentan-2-one.

Each clue narrows it down. C₅H₁₀O with no Tollens' reaction is a ketone, not an aldehyde, so pentanal is out. Forming a bisulphite adduct and giving the iodoform test both point to a methyl ketone, CH₃CO-R.

Pentan-2-one, CH₃COCH₂CH₂CH₃, fits, and vigorous oxidation cleaves it beside the carbonyl to give ethanoic acid and propanoic acid.

Pentan-3-one has no CH₃CO group and fails the iodoform test. Ethoxyethane and pentanol are not carbonyl compounds (and ethoxyethane is C₄H₁₀O).

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38.

In aldol condensation reaction, 1, 3-diphenylprop-2-en-1--one is obtained as major product in the reaction between

A.benzaldehyde and benzophenone
B.benzaldehyde and acetophenone
C.propan-2-one and benzaldehyde
D.acetophenone and propan-2-one
E.benzaldehye and butan-2-one

Exam Year(s)

KEAM - 2026,

Answer: B

The reactants are benzaldehyde and acetophenone.

1,3-Diphenylprop-2-en-1-one is C₆H₅CO-CH=CH-C₆H₅ (chalcone). It forms by a crossed aldol (Claisen-Schmidt) condensation: the enolate of acetophenone, C₆H₅COCH₃, adds to benzaldehyde, which has no alpha-hydrogen, and the product loses water to give the conjugated enone.

Benzophenone has no alpha-hydrogens, so with benzaldehyde neither partner can form an enolate. Propan-2-one or butan-2-one with benzaldehyde give products with methyl or ethyl groups, not a second phenyl ring, and acetophenone with propan-2-one gives no benzylidene unit.

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39.

Which of the following is a commercial method of manufacture of benzaldehyde?

A.Hydrogenation of benzoylchloride with Pd/\(\mathrm{BaSO_4}\) as catalyst.
B.Oxidation of toluene with chromyl chloride followed by hydrolysis
C.Toluene is treated with \(\mathrm{Cr_2O_3}\) in acetic anhydride followed by hydrolysis
D.Side chain chlorination of toluene followed by hydrolysis.
E.Benzene is treated with CO and HClin the presence of anhydrous \(\mathrm{AlCl_3}\).

Exam Year(s)

KEAM - 2026,

Answer: D

The commercial method is side chain chlorination of toluene followed by hydrolysis.

Chlorinating toluene in the side chain gives benzal chloride, C₆H₅CHCl₂, which is hydrolysed to benzaldehyde. This is the method used industrially.

The other routes are laboratory methods: the Rosenmund reduction of benzoyl chloride, the Etard reaction with chromyl chloride, oxidation with chromic oxide in acetic anhydride (CrO₃, though the option prints Cr₂O₃), and the Gattermann-Koch reaction with CO and HCl.

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40.

Which is the reagent used for the following conversion?

A cyclohexanone ring with a CHO group opposite the C=O is converted by an arrow into the same ring with COO minus in place of CHO

A.NaCN/HCl
B.\(\mathrm{NaBH_{4}}\)
C.\(\mathrm{SOCl_{2}}\)
D.\(\mathrm{O_{3}/Zn{-}H_{2}O}\)
E.\(\mathrm{[Ag(NH_{3})_{2}]^{+}}\)

Exam Year(s)

KEAM - 2026,

Answer: E

The reagent is [Ag(NH₃)₂]⁺, Tollens' reagent.

The conversion oxidises the aldehyde group to a carboxylate while leaving the ring ketone untouched. Tollens' reagent is a mild oxidising agent that oxidises aldehydes to carboxylate ions (and deposits a silver mirror) but does not attack ketones, so it is selective.

NaBH₄ reduces carbonyl groups; NaCN/HCl adds HCN to them; SOCl₂ converts acids or alcohols to chlorides; and ozonolysis cleaves C=C double bonds. None oxidises CHO to COO^-.

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