How many MCQs come from Aldehydes and Ketones in MDCAT?

Aldehydes and Ketones typically contribute 2–3 MCQs in MDCAT Chemistry. The chapter is high-yield because the distinguishing tests (Tollens, Fehling, iodoform) and the reactivity order of aldehydes versus ketones are frequently repeated.

Aldehydes and Ketones MDCAT Notes, MCQs & Past Papers – Nomenclature, Nucleophilic Addition, Tests

Q: What is the difference between an aldehyde and a ketone?

In an aldehyde, the carbonyl carbon is bonded to at least one hydrogen atom (general formula R-CHO). In a ketone, the carbonyl carbon is bonded to two carbon groups (general formula R-CO-R'). Aldehydes end in '-al', ketones in '-one'. Aldehydes are more reactive than ketones toward nucleophilic addition.

Q: Why are aldehydes more reactive than ketones?

Aldehydes are more reactive for two reasons: (1) Electronic - ketones have two electron-donating alkyl groups that reduce the positive character (δ+) of the carbonyl carbon. (2) Steric - the two alkyl groups in ketones cause more hindrance for approaching nucleophiles, while aldehydes have only one small hydrogen.

Q: What is the Tollens' test used for?

Tollens' test (silver mirror test) distinguishes aldehydes from ketones. Aldehydes reduce Tollens' reagent (ammoniacal silver nitrate) to metallic silver, forming a silver mirror on the test tube walls. Ketones do not react. The aldehyde is oxidized to a carboxylate salt.

Q: What is the 2,4-DNP test?

The 2,4-DNP (2,4-dinitrophenylhydrazine, Brady's reagent) test confirms the presence of a carbonyl group (aldehyde or ketone). Both aldehydes and ketones react with 2,4-DNPH to form a yellow or orange precipitate (a 2,4-dinitrophenylhydrazone). It does NOT distinguish aldehydes from ketones.

Q: What is the Iodoform test?

The iodoform test uses I₂ and NaOH to detect methyl ketones (R-CO-CH₃) and certain alcohols/aldehydes with a CH₃-CH(OH)- or CH₃-CO- group (like ethanol, acetaldehyde, and 2-propanol). A yellow precipitate of iodoform (CHI₃) forms. It distinguishes methyl ketones from other ketones.

Q: What is Cannizzaro's reaction?

Cannizzaro's reaction is the disproportionation of aldehydes lacking α-hydrogens (e.g., formaldehyde, benzaldehyde) in concentrated base. One molecule of aldehyde is oxidized to a carboxylate salt, while another is reduced to a primary alcohol. Example: 2HCHO + NaOH → CH₃OH + HCOONa.

Q: What is Aldol condensation?

Aldol condensation is a base-catalyzed reaction between two carbonyl compounds that have α-hydrogens. One molecule forms an enolate ion, which attacks the carbonyl of the other, giving a β-hydroxy aldehyde or ketone (aldol). This often undergoes dehydration to form an α,β-unsaturated carbonyl compound.

Q: What is Clemmensen reduction?

Clemmensen reduction uses zinc amalgam and concentrated HCl (Zn-Hg/HCl) to reduce the carbonyl group (C=O) of aldehydes and ketones to a methylene group (-CH₂-). It works under acidic conditions, so it may not suit acid-sensitive substrates.

⚗️ Chemistry · Aldehydes & Ketones

📅 Updated Jan 2026 ⏱️ 30 min read 🎯 High-yield

Aldehydes & Ketones — Nucleophilic Addition, Reduction & Tests

Complete MDCAT Chemistry chapter on aldehydes and ketones: nomenclature, preparation, reactivity differences, nucleophilic addition (cyanohydrin, acetal, Grignard), reduction, oxidation, and distinguishing tests (Tollens, Fehling, 2,4-DNP, iodoform). Includes 200 solved MCQs with explanations and year-wise past papers.

⚡Quick Answers to Common Searches

Direct, snippet-optimized answers to the top questions students search about aldehydes and ketones.

What is an aldehyde?

An aldehyde has a carbonyl carbon bonded to at least one hydrogen (R–CHO). IUPAC suffix: -al. Example: methanal (HCHO), ethanal (CH₃CHO).

What is a ketone?

A ketone has a carbonyl carbon bonded to two carbon groups (R–CO–R'). IUPAC suffix: -one. Example: propanone (CH₃COCH₃).

Aldehyde vs ketone?

Aldehydes: carbonyl bonded to ≥1 H, more reactive. Ketones: carbonyl bonded to 2 C-groups, less reactive (electronic + steric reasons).

Why are aldehydes more reactive?

Two reasons: (1) ketones have two electron-donating alkyl groups (reduce δ+ on carbonyl C); (2) ketones have more steric hindrance for incoming nucleophiles.

What is nucleophilic addition?

Characteristic reaction of C=O. Nucleophile attacks the electrophilic carbonyl carbon → tetrahedral alkoxide intermediate → protonation. Examples: HCN, Grignard, NaHSO₃.

Tollens' test?

Ammoniacal AgNO₃. Aldehydes give a silver mirror (Ag⁺ → Ag). Ketones do NOT react. Classic distinguishing test.

Fehling's test?

Cu²⁺ in alkaline tartrate. Aliphatic aldehydes give brick-red Cu₂O precipitate. Ketones and aromatic aldehydes (e.g., benzaldehyde) give no reaction.

2,4-DNP test?

2,4-DNP (Brady's reagent) gives yellow/orange ppt with both aldehydes and ketones. Confirms C=O presence but does NOT distinguish between the two.

Iodoform test?

I₂ + NaOH gives yellow CHI₃ precipitate with methyl ketones (CH₃CO–R) and acetaldehyde (CH₃CHO). Distinguishes methyl ketones from others.

Cannizzaro's reaction?

Disproportionation of aldehydes without α-H (HCHO, ArCHO) in concentrated base. One molecule oxidized to acid, another reduced to alcohol.

Aldol condensation?

Base-catalyzed reaction between carbonyls with α-H. One forms an enolate, attacks the other → β-hydroxy carbonyl (aldol) → often dehydrates to α,β-unsaturated carbonyl.

Clemmensen reduction?

Zn-Hg / HCl converts C=O → CH₂ (methylene). Works in acid. Not suitable for acid-sensitive groups.

Wolff-Kishner reduction?

NH₂NH₂ / KOH converts C=O → CH₂. Works in base. Preferred for acid-sensitive substrates.

Grignard reactions?

+ HCHO → 1° alcohol; + other aldehydes → 2° alcohol; + ketones → 3° alcohol; + CO₂ → carboxylic acid.

Formalin?

Formalin = ~40% formaldehyde in water, with methanol as stabilizer. Used as disinfectant and biological preservative.

❓People Also Ask — Aldehydes & Ketones

Questions students most frequently search about this chapter. Answers are direct and exam-focused.

QWhat is the difference between an aldehyde and a ketone?

In an aldehyde, the carbonyl carbon is bonded to at least one hydrogen (R-CHO). In a ketone, the carbonyl carbon is bonded to two carbon groups (R-CO-R'). Aldehydes end in "-al", ketones in "-one". Aldehydes are more reactive toward nucleophilic addition.

QWhy are aldehydes more reactive than ketones?

Aldehydes are more reactive because: (1) Electronic — ketones have two electron-donating alkyl groups that reduce the δ+ character of the carbonyl carbon. (2) Steric — two alkyl groups in ketones cause more hindrance for approaching nucleophiles.

QWhat is nucleophilic addition?

It's the characteristic reaction of the carbonyl group. A nucleophile attacks the electrophilic carbon, the C=O π-bond breaks, giving a tetrahedral sp³ alkoxide intermediate that is protonated. Examples: HCN (cyanohydrin), NaHSO₃, Grignard, alcohol (acetal).

QWhat is the Tollens' test used for?

Tollens' test (silver mirror) distinguishes aldehydes from ketones. Aldehydes reduce ammoniacal silver nitrate to metallic silver (silver mirror). Ketones do not react.

QWhat is the Fehling's test used for?

Fehling's test distinguishes aliphatic aldehydes from ketones and aromatic aldehydes. Fehling's solution (Cu²⁺ in alkaline tartrate) is reduced by aliphatic aldehydes to a brick-red Cu₂O precipitate. Ketones and aromatic aldehydes (like benzaldehyde) give a negative test.

QWhat is the 2,4-DNP test?

The 2,4-DNP (Brady's reagent) test confirms the presence of a carbonyl group. Both aldehydes and ketones give a yellow/orange precipitate (2,4-dinitrophenylhydrazone). It does NOT distinguish aldehydes from ketones.

QWhat is the Iodoform test?

The iodoform test uses I₂ and NaOH to detect methyl ketones (R-CO-CH₃) and acetaldehyde. A yellow precipitate of iodoform (CHI₃) forms. It distinguishes methyl ketones from other ketones.

QWhat is Cannizzaro's reaction?

Disproportionation of aldehydes lacking α-hydrogens (formaldehyde, benzaldehyde) in concentrated base. One molecule oxidizes to carboxylate salt, another reduces to primary alcohol. Example: 2HCHO + NaOH → CH₃OH + HCOONa.

QWhat is Aldol condensation?

Base-catalyzed reaction between two carbonyls that have α-hydrogens. One forms an enolate ion, attacks the other's carbonyl → β-hydroxy aldehyde/ketone (aldol). Often dehydrates to form α,β-unsaturated carbonyl.

QWhat is Clemmensen reduction?

Clemmensen reduction uses Zn-Hg/HCl to reduce C=O → CH₂. It works under acidic conditions, so acid-sensitive groups may not survive.

QWhat is Wolff-Kishner reduction?

Wolff-Kishner reduction uses NH₂NH₂ and KOH to reduce C=O → CH₂. It works under basic conditions, so preferred for acid-sensitive compounds.

QHow can aldehydes be prepared?

(1) Controlled oxidation of primary alcohols; (2) ozonolysis of alkenes; (3) hydration of terminal alkynes (gives aldehyde only for ethyne); (4) Rosenmund reduction of acyl chlorides; (5) dry distillation of calcium formate with calcium acetate.

QHow can ketones be prepared?

(1) Oxidation of secondary alcohols; (2) dry distillation of calcium carboxylates (except formate); (3) hydration of alkynes other than ethyne; (4) Friedel-Crafts acylation; (5) Grignard addition to nitriles followed by hydrolysis.

QWhat are the products of Grignard reagent with different carbonyls?

RMgX + formaldehyde → primary alcohol. + other aldehydes → secondary alcohol. + ketones → tertiary alcohol. + CO₂ → carboxylic acid.

QWhy is Fehling's test negative for aromatic aldehydes?

Aromatic aldehydes like benzaldehyde are not oxidized by Fehling's solution (weaker oxidizing agent) due to resonance stabilization of the aromatic ring. They DO react with Tollens' reagent (stronger oxidant).

QWhat is the Cannizzaro reaction of benzaldehyde?

Benzaldehyde (no α-H) undergoes disproportionation: 2PhCHO + NaOH → PhCH₂OH (benzyl alcohol) + PhCOONa (sodium benzoate).

QWhat is the Rosemund reduction?

Rosenmund reduction: RCOCl + H₂ (Pd/BaSO₄ poisoned) → RCHO + HCl. The poisoned catalyst (BaSO₄ + quinoline) prevents over-reduction to alcohol.

QWhat is Popoff's rule?

Popoff's rule states that during oxidation of unsymmetrical ketones, the carbonyl group stays with the smaller alkyl group. Example: butanone → ethanoic acid + propanoic acid.

QHow many MCQs from Aldehydes & Ketones in MDCAT?

Aldehydes and Ketones typically contribute 2–3 MCQs. High-yield because distinguishing tests (Tollens, Fehling, iodoform) are frequently repeated.

QWhat is formalin?

Formalin is ~40% formaldehyde in water, with methanol as stabilizer. Used as disinfectant and biological preservative.

📋Syllabus & Learning Outcomes

According to PMDC/PMC MDCAT syllabus, Aldehydes and Ketones cover:

Explain nomenclature and structure of aldehydes and ketones.
Discuss the preparation of aldehydes and ketones.
Describe reactivity of aldehydes and ketones and their comparison.
Describe acid and base catalyzed nucleophilic addition reactions of aldehydes and ketones.
Discuss the chemistry of aldehydes and ketones by their reduction to alcohols.
Describe oxidation reactions of aldehydes and ketones.

📝Full Notes — Aldehydes & Ketones

1. Nomenclature & Structure

Functional group: Carbonyl group (>C=O).
Aldehyde: Carbonyl carbon bonded to at least one H; suffix -al. e.g., methanal (HCHO), ethanal (CH₃CHO).
Ketone: Carbonyl carbon bonded to two alkyl/aryl groups; suffix -one. e.g., propanone (CH₃COCH₃), butan-2-one.
Carbonyl carbon is sp² hybridised, trigonal planar (~120°).
Polar bond (O δ⁻, C δ⁺) → reactivity with nucleophiles.

2. Preparation of Aldehydes & Ketones

Oxidation of alcohols:
- 1° alcohol → aldehyde (controlled oxidation, e.g., PCC) → carboxylic acid.
- 2° alcohol → ketone (e.g., K₂Cr₂O₇/H⁺).
Ozonolysis of alkenes: Alkene + O₃ → carbonyl compounds (Zn/H₂O workup).
Hydration of alkynes: Alkyne + H₂O, HgSO₄/H₂SO₄ → enol → tautomerises to carbonyl; terminal alkyne → methyl ketone.
Friedel-Crafts acylation: Aromatic + acyl chloride (AlCl₃) → aryl ketone.
Rosenmund reduction: Acyl chloride + H₂, Pd/BaSO₄ → aldehyde.

3. Reactivity of Aldehydes vs Ketones

Both undergo nucleophilic addition (Nu⁻ attacks electrophilic carbonyl C).
Aldehydes are more reactive than ketones because:
- Steric: Aldehyde has one small H (less hindrance).
- Electronic: Ketone has two electron-donating alkyl groups, stabilising the δ⁺ carbon and making it less electrophilic.
Formaldehyde is the most reactive aldehyde (two H atoms).

4. Acid & Base Catalyzed Nucleophilic Addition

Base-catalyzed: Strong nucleophile attacks carbonyl directly; then protonation. e.g., NaCN addition → cyanohydrin.
Acid-catalyzed: Carbonyl oxygen is protonated first → increases electrophilicity of C; then weaker nucleophile (H₂O, ROH) attacks. e.g., acetal formation.
Key reactions:
- + HCN → cyanohydrin (base-catalyzed).
- + NaHSO₃ → bisulfite adduct (crystalline derivative).
- + Alcohol (dry HCl) → hemiacetal → acetal (aldehyde); hemiketal → ketal (ketone).
- + Ammonia derivatives (NH₂-G): e.g., NH₂OH → oxime, NH₂-NH₂ → hydrazone, 2,4-DNP → yellow/orange ppt (test for carbonyl).
- + Grignard reagent → alcohol (formaldehyde → 1°, other aldehydes → 2°, ketones → 3°).

5. Reduction to Alcohols

Catalytic hydrogenation: H₂, Ni/Pt/Pd → aldehyde → 1° alcohol; ketone → 2° alcohol.
Metal hydrides: NaBH₄ (selective, reduces only aldehydes/ketones) or LiAlH₄ (stronger, also reduces acids/esters).
Aldehyde + NaBH₄ → 1° alcohol; ketone + NaBH₄ → 2° alcohol.
Trap: LiAlH₄ also reduces C=C conjugated with C=O, but NaBH₄ does not.

6. Oxidation Reactions

Aldehydes: Easily oxidised to carboxylic acids.
- Mild oxidants: Tollens' reagent (Ag⁺/NH₃ → Ag mirror), Fehling's solution (Cu²⁺ → Cu₂O red ppt), Benedict's solution.
- These are tests for aldehydes (ketones give negative result).
- Strong oxidants: KMnO₄, K₂Cr₂O₇/H⁺ also oxidise aldehydes to acids.
Ketones: Resistant to mild oxidants; vigorous oxidation cleaves the carbon chain (gives mixture of carboxylic acids).
Key distinction: Aldehydes give positive Tollens/Fehling test; ketones do not.

High-Yield Points & Common Traps

Aldehyde suffix -al, ketone -one; both have carbonyl >C=O.
Aldehydes more reactive than ketones (steric + electronic reasons).
Nucleophilic addition mechanism; acid vs base catalysis.
NaBH₄ reduces only aldehydes/ketones; LiAlH₄ is stronger.
2,4-DNP test: yellow/orange precipitate = carbonyl present.
Tollens' test (silver mirror) and Fehling's test (red ppt) distinguish aldehydes from ketones.
Oxidation: aldehyde → carboxylic acid; ketones resist mild oxidation.
Ozonolysis of alkenes → carbonyl compounds.
Grignard + formaldehyde → 1° alcohol; + other aldehydes → 2° alcohol; + ketone → 3° alcohol.
Traps: "Ketones give positive Tollens' test" → False. "Ketones are more reactive than aldehydes" → False. "NaBH₄ reduces carboxylic acids" → False.

✅Practice MCQs — Test 1

🧪 Basic Concepts

50 MCQs

1The hybridization of the carbonyl carbon in aldehydes and ketones is:

A. sp
B. sp²
C. sp³
D. dsp²

Answer: B. sp²

The carbonyl carbon is sp² hybridized, forming three σ bonds (one to oxygen, two to other atoms) and one π bond.

2The IUPAC name of the simplest ketone is:

A. Ethanal
B. Propanal
C. Propanone
D. Butanone

Answer: C. Propanone

Propanone (acetone, CH₃COCH₃) is the simplest ketone with three carbons.

3In the carbonyl group (>C=O), the bond angle is approximately:

A. 109.5°
B. 120°
C. 180°
D. 90°

Answer: B. 120°

The carbonyl carbon is sp² hybridized, giving a trigonal planar geometry with bond angles of about 120°.

4Formaldehyde is also known as:

A. Ethanal
B. Methanal
C. Propionaldehyde
D. Butanal

Answer: B. Methanal

Formaldehyde is the common name for methanal (HCHO).

5Which of the following represents the general formula for a saturated aliphatic ketone?

A. CₙH₂ₙ₊₂O
B. CₙH₂ₙO
C. CₙH₂ₙ₋₂O
D. CₙH₂ₙ₊₁O

Answer: B. CₙH₂ₙO

Saturated ketones have one degree of unsaturation (C=O) so formula CₙH₂ₙO.

6The oxidation of a primary alcohol with acidified K₂Cr₂O₇ primarily yields:

A. A ketone
B. An aldehyde
C. An ester
D. An ether

Answer: B. An aldehyde

Primary alcohols are first oxidized to aldehydes; further oxidation gives carboxylic acids. Distillation can isolate the aldehyde.

7Ketones are produced by the oxidation of:

A. Primary alcohols
B. Secondary alcohols
C. Tertiary alcohols
D. Phenols

Answer: B. Secondary alcohols

Secondary alcohols (R₂CHOH) oxidize to ketones (R₂C=O).

8Calcium acetate on dry distillation gives:

A. Formaldehyde
B. Acetaldehyde
C. Acetone
D. Propionaldehyde

Answer: C. Acetone

Calcium acetate → acetone (CH₃COCH₃) + CaCO₃.

9Hydration of ethyne (C₂H₂) in the presence of HgSO₄/H₂SO₄ produces:

A. Methanal
B. Ethanal
C. Propanone
D. Ethanol

Answer: B. Ethanal

Hg²⁺/H⁺ catalyzes Markovnikov addition of water to ethyne, giving vinyl alcohol which tautomerizes to acetaldehyde.

10The industrial preparation of formaldehyde involves the oxidation of methanol over which catalyst?

A. Ni at 300°C
B. Fe₂O₃ + MoO₃ at 500°C
C. Al₂O₃
D. V₂O₅

Answer: B

Methanol vapor and air over iron-molybdenum oxide catalyst at ~500°C gives formaldehyde.

11The Carbonyl group is polar because:

A. Oxygen is more electronegative than Carbon
B. Carbon is more electronegative than Oxygen
C. It contains a double bond
D. It is sp² hybridized

Answer: A

Oxygen (3.44) is more electronegative than carbon (2.55), creating a dipole with carbon δ⁺ and oxygen δ⁻.

12Which of the following is most reactive towards nucleophilic addition?

A. Formaldehyde
B. Acetaldehyde
C. Acetone
D. Diethyl ketone

Answer: A. Formaldehyde

Formaldehyde has no alkyl groups to donate electrons (no +I effect) and is least sterically hindered, making it most reactive.

13Ketones are less reactive than aldehydes because of:

A. Inductive effect of two alkyl groups
B. Steric hindrance
C. Presence of alpha-hydrogens
D. Both A and B

Answer: D

Alkyl groups donate electrons (+I effect) reducing the electrophilicity of the carbonyl carbon, and also cause steric hindrance.

14In the carbonyl group, the carbon atom acts as:

A. A nucleophile
B. An electrophile
C. A free radical
D. A base

Answer: B. An electrophile

The carbon is partially positive (δ⁺) and is attacked by nucleophiles.

15The nucleophile in a reaction attacks which part of the carbonyl group?

A. Oxygen atom
B. Carbon atom
C. Lone pair on oxygen
D. Pi-bond directly

Answer: B. Carbon atom

Nucleophiles attack the electrophilic carbon atom.

16Formaldehyde is a gas at room temperature, while higher aldehydes are liquids or solids. This is due to:

A. Hydrogen bonding
B. Van der Waals forces
C. Dipole-dipole interactions
D. Ion-dipole forces

Answer: A

Aldehydes cannot form strong intermolecular H-bonds (no O-H bond), so London forces dominate. Formaldehyde has low molecular mass, thus gas.

17Which of the following will have the highest boiling point?

A. Propanal
B. Propanone
C. n-Butane
D. Propan-1-ol

Answer: D. Propan-1-ol

Propan-1-ol has O-H group, allowing strong intermolecular hydrogen bonding, giving highest boiling point.

18The boiling points of aldehydes and ketones are higher than those of alkanes but lower than alcohols because:

A. They form intermolecular H-bonds
B. They have dipole-dipole interactions
C. They are non-polar
D. They have ionic character

Answer: B

Aldehydes and ketones have polar C=O, leading to dipole-dipole interactions, but no O-H, so weaker than alcohols.

19Acetone and Propanal are:

A. Chain isomers
B. Position isomers
C. Functional group isomers
D. Metamers

Answer: C

Both have formula C₃H₆O; acetone is a ketone, propanal is an aldehyde → functional group isomers.

20Which of the following does not have an α-hydrogen?

A. Ethanal
B. Propanone
C. Benzaldehyde
D. Butanal

Answer: C. Benzaldehyde

Benzaldehyde (C₆H₅CHO) has no α-hydrogen because the aldehyde carbon is directly attached to the benzene ring.

21The reaction of an aldehyde with HCN follows which mechanism?

A. Electrophilic addition
B. Nucleophilic substitution
C. Nucleophilic addition
D. Free radical addition

Answer: C

CN⁻ attacks the carbonyl carbon, followed by protonation → cyanohydrin (nucleophilic addition).

22In base-catalyzed nucleophilic addition, the catalyst increases the reactivity of:

A. The carbonyl group
B. The nucleophile
C. The electrophile
D. The solvent

Answer: B

Base deprotonates the nucleophile (e.g., H₂O → OH⁻), making it a stronger nucleophile.

23In acid-catalyzed nucleophilic addition, the catalyst (H⁺) increases the reactivity of:

A. The nucleophile
B. The carbonyl carbon (by protonating oxygen)
C. The leaving group
D. The alkyl group

Answer: B

Protonation of the carbonyl oxygen increases the positive charge on carbon, making it more electrophilic.

24The addition of Sodium Bisulfite (NaHSO₃) to aldehydes and methyl ketones is used for:

A. Oxidation
B. Reduction
C. Purification and separation
D. Substitution

Answer: C

Bisulfite adducts are crystalline and can be regenerated, used for purification.

25Reaction of acetaldehyde with ethylmagnesium bromide followed by hydrolysis yields:

A. Ethanol
B. 1-Butanol
C. 2-Butanol
D. 2-Methyl-2-propanol

Answer: C. 2-Butanol

CH₃CHO + C₂H₅MgBr → CH₃CH(OH)C₂H₅ (2-butanol, secondary).

26Formaldehyde reacts with Grignard reagent to produce:

A. Primary alcohol
B. Secondary alcohol
C. Tertiary alcohol
D. Ketone

Answer: A. Primary alcohol

HCHO + RMgX → RCH₂OH (primary alcohol after hydrolysis).

27Addition of ammonia derivatives (G-NH₂) to carbonyl compounds is usually:

A. Purely addition
B. Addition followed by elimination of water
C. Purely substitution
D. Polymerization

Answer: B

Nucleophilic addition forms a carbinolamine, then dehydration gives imine (Schiff base), oxime, hydrazone, etc.

28Acetaldehyde reacts with hydroxylamine (NH₂OH) to form:

A. An oxime
B. A hydrazone
C. A phenylhydrazone
D. A semi-carbazone

Answer: A. An oxime

Acetaldehyde oxime: CH₃CH=NOH.

29The reaction of acetone with 2,4-dinitrophenylhydrazine (2,4-DNPH) yields a precipitate of:

A. Yellow or Orange color
B. White color
C. Blue color
D. No precipitate

Answer: A

2,4-DNPH gives yellow/orange precipitates (hydrazones) with almost all aldehydes and ketones.

30Which of the following gives a silver mirror with Tollen's reagent?

A. Acetone
B. Acetaldehyde
C. Diethyl ketone
D. Ethyl methyl ketone

Answer: B. Acetaldehyde

Tollen's reagent (ammoniacal AgNO₃) oxidizes aldehydes to acids, depositing metallic silver. Ketones do not react.

31Fehling's solution is used to detect the presence of:

A. Ketones
B. Aldehydes
C. Alcohols
D. Ethers

Answer: B. Aldehydes

Fehling's solution (Cu²⁺ in alkaline tartrate) oxidizes aliphatic aldehydes, giving brick-red Cu₂O precipitate.

32A positive Benedict's test is indicated by the formation of a:

A. Silver mirror
B. Red precipitate of Cu₂O
C. White precipitate
D. Yellow precipitate

Answer: B

Benedict's test is similar to Fehling's; reducing sugars and aldehydes give Cu₂O (red).

33Ketones are resistant to oxidation because:

A. They have no α-hydrogen
B. They lack a hydrogen atom attached to the carbonyl carbon
C. They are too bulky
D. They are more acidic

Answer: B

Oxidation requires a hydrogen on the carbonyl carbon (aldehydes have one; ketones have none).

34Oxidation of symmetrical ketones with strong oxidizing agents (KMnO₄/H⁺) results in:

A. Only one type of carboxylic acid
B. Mixture of carboxylic acids with shorter chains
C. An aldehyde
D. An alcohol

Answer: B

Symmetrical ketones (R-CO-R) give two molecules of the same carboxylic acid (RCOOH).

35The Iodoform test is given by:

A. All aldehydes
B. All ketones
C. Methyl ketones and Acetaldehyde
D. Only Formaldehyde

Answer: C

Compounds with CH₃CO- group (methyl ketones) or CH₃CH(OH)- group (e.g., ethanol, 2-propanol) give iodoform test.

36Which of the following will not give a positive Iodoform test?

A. Ethanol
B. Acetone
C. Pentan-3-one
D. Acetaldehyde

Answer: C

Pentan-3-one (CH₃CH₂COCH₂CH₃) has no methyl group adjacent to the carbonyl, so no iodoform.

37Reduction of aldehydes with LiAlH₄ or NaBH₄ produces:

A. Primary alcohols
B. Secondary alcohols
C. Tertiary alcohols
D. Alkanes

Answer: A. Primary alcohols

RCHO → RCH₂OH.

38Reduction of ketones with NaBH₄ produces:

A. Primary alcohols
B. Secondary alcohols
C. Tertiary alcohols
D. Alkanes

Answer: B. Secondary alcohols

R₂C=O → R₂CHOH.

39The Clemmensen reduction (Zn-Hg/HCl) converts a carbonyl group into a:

A. -CH₂- group (Alkane)
B. -CHOH- group (Alcohol)
C. -COOH group (Acid)
D. -CH₃ group

Answer: A

C=O → CH₂ under acidic reducing conditions.

40Wolff-Kishner reduction (NH₂-NH₂ / KOH) is used to reduce carbonyl compounds into:

A. Alcohols
B. Alkanes
C. Ethers
D. Amines

Answer: B. Alkanes

C=O → CH₂ under basic conditions via hydrazone intermediate.

41Aldehydes can be distinguished from ketones by using:

A. HCN
B. NaHSO₃
C. Tollen's reagent
D. 2,4-DNPH

Answer: C

Tollen's reagent reacts with aldehydes (silver mirror) but not with ketones. 2,4-DNPH reacts with both.

42The reaction of an aldehyde with an alcohol in the presence of dry HCl gas forms:

A. An acetal
B. An ester
C. An ether
D. A ketone

Answer: A. An acetal

RCHO + 2 R'OH → RCH(OR')₂ (acetal) + H₂O.

43Cannizzaro's reaction is given by:

A. Aldehydes with α-hydrogen
B. Aldehydes without α-hydrogen
C. All ketones
D. All alcohols

Answer: B

Aldehydes lacking α-hydrogens (e.g., HCHO, ArCHO) undergo disproportionation in concentrated base.

44Which of the following undergoes Cannizzaro's reaction?

A. Acetaldehyde
B. Formaldehyde
C. Propionaldehyde
D. Acetone

Answer: B. Formaldehyde

Formaldehyde has no α-hydrogen, so it undergoes Cannizzaro to give methanol and formate.

45Aldol condensation requires the presence of:

A. At least one α-hydrogen
B. No α-hydrogen
C. A strong oxidizing agent
D. A silver catalyst

Answer: A

The enolate formation requires α-hydrogens on at least one of the carbonyl compounds.

46The product of Aldol condensation of acetaldehyde is:

A. 3-Hydroxybutanal
B. 2-Hydroxybutanal
C. Butan-2-ol
D. Ethanol and Acetic acid

Answer: A

Two molecules of acetaldehyde condense to form 3-hydroxybutanal (aldol).

47Formalin is a solution of:

A. 10% formaldehyde
B. 40% formaldehyde
C. 90% formaldehyde
D. 100% formaldehyde

Answer: B. 40% formaldehyde

Formalin is about 40% formaldehyde in water (with some methanol to prevent polymerization).

48Acetone is used as:

A. A nail polish remover
B. A preservative for biological specimens
C. An anesthetic
D. A beverage

Answer: A

Acetone is a common solvent in nail polish removers and industrial applications.

49According to Popoff's rule, during oxidation of unsymmetrical ketones:

A. The carbonyl group stays with the smaller alkyl group
B. The carbonyl group stays with the larger alkyl group
C. The molecule does not break
D. Only CO₂ is formed

Answer: A

In unsymmetrical ketones, the carbonyl group remains attached to the smaller alkyl group upon cleavage.

50Paraldehyde is a trimer of:

A. Formaldehyde
B. Acetaldehyde
C. Acetone
D. Propanal

Answer: B. Acetaldehyde

Three molecules of acetaldehyde polymerize to form paraldehyde (cyclic trimer).

✅Practice MCQs — Test 2

🧪 Advanced Concepts

50 MCQs

1Which of the following describes the nature of the C=O bond most accurately?

A. A σ-bond formed by sp²-sp² overlap and a π-bond by p-p overlap
B. A σ-bond formed by sp³-sp² overlap and a π-bond by p-p overlap
C. Two π-bonds formed by lateral overlap
D. A σ-bond formed by sp²-p overlap

Answer: A

Carbonyl carbon is sp² hybridized; σ bond is sp² (C) with sp² or sp³ of other atom; π bond is p-p lateral overlap.

2Arrange the following in decreasing order of reactivity towards nucleophilic addition: I. HCHO, II. CH₃CHO, III. CH₃COCH₃, IV. C₆H₅CHO

A. I > II > IV > III
B. I > II > III > IV
C. IV > III > II > I
D. II > I > III > IV

Answer: A

Electron-withdrawing groups increase reactivity; electron-donating decrease. Order: HCHO > CH₃CHO > C₆H₅CHO > (CH₃)₂CO.

3In the acid-catalyzed addition of a nucleophile to a carbonyl group, the first step is:

A. Attack of the nucleophile on the carbonyl carbon
B. Protonation of the carbonyl oxygen to increase electrophilicity of carbon
C. Deprotonation of the nucleophile
D. Breaking of the C=O π-bond

Answer: B

Protonation of oxygen makes the carbon more δ⁺, facilitating nucleophilic attack.

4Which of the following will yield Benzaldehyde upon Rosenmund Reduction?

A. Benzoyl chloride + H₂ / Pd-BaSO₄
B. Benzyl alcohol + KMnO₄
C. Chlorobenzene + NaOH
D. Benzene + CO / HCl

Answer: A

Rosenmund reduction: RCOCl + H₂ → RCHO + HCl, using poisoned Pd/BaSO₄.

5Dry distillation of a mixture of Calcium Formate and Calcium Acetate yields primarily:

A. Methanal
B. Ethanal
C. Propanone
D. A mixture of all three, but Ethanal is the cross-product

Answer: B. Ethanal

(HCOO)₂Ca + (CH₃COO)₂Ca → 2CH₃CHO + 2CaCO₃ (cross product).

6Stephen's Reduction involves the conversion of Nitriles (R-CN) to Aldehydes using:

A. SnCl₂ / HCl followed by hydrolysis
B. LiAlH₄
C. H₂ / Ni
D. NaBH₄

Answer: A

R-CN + SnCl₂/HCl → iminium salt → hydrolysis gives RCHO.

7The transition state of a nucleophilic attack on a carbonyl carbon changes the geometry from:

A. Trigonal planar to Tetrahedral
B. Tetrahedral to Trigonal planar
C. Linear to Bent
D. Trigonal planar to Trigonal bipyramidal

Answer: A

The carbonyl carbon goes from sp² (trigonal planar) to sp³ (tetrahedral) in the tetrahedral intermediate.

8Which of the following has the highest dipole moment?

A. Propanone
B. Propanal
C. Diethyl ether
D. n-Butane

Answer: A

Propanone has the most polar C=O bond; the dipole is not cancelled by symmetry.

9Ozonolysis of 2-Methyl-2-butene produces:

A. Two moles of Acetaldehyde
B. Propanone and Acetaldehyde
C. Propanone and Formaldehyde
D. Butanone and Methanal

Answer: B

2-Methyl-2-butene (CH₃)₂C=CHCH₃ ozonolysis gives acetone (CH₃)₂C=O and acetaldehyde CH₃CHO.

10The formation of a Cyanohydrin from a ketone is a reversible reaction. To shift the equilibrium to the right, we use:

A. High concentration of H₂SO₄
B. A base to maintain a steady concentration of CN⁻ ions
C. Low temperature and high pressure
D. An oxidizing agent

Answer: B

Base generates CN⁻, and since HCN is weak acid, adding base favors CN⁻ and shifts equilibrium to product.

11In the base-catalyzed Aldol condensation, the reactive intermediate is:

A. A carbocation
B. An enolate ion (carbanion)
C. A free radical
D. An oxonium ion

Answer: B

Base abstracts α-hydrogen to form enolate, which attacks another carbonyl.

12Which of the following will NOT undergo Aldol condensation?

A. Propanal
B. 2,2-Dimethylpropanal
C. 2-Methylpropanal
D. Acetone

Answer: B

2,2-Dimethylpropanal (pivalaldehyde) has no α-hydrogens, so cannot form enolate.

13The major product of the reaction between Benzaldehyde and Acetophenone in the presence of dilute NaOH (Claisen-Schmidt reaction) is:

A. Benzyl alcohol
B. 1,3-Diphenyl-2-propene-1-one (Chalcone)
C. Benzoic acid
D. Sodium benzoate

Answer: B

Cross-aldol followed by dehydration gives α,β-unsaturated ketone (chalcone).

14In Cannizzaro's reaction, the disproportionation involves:

A. Simultaneous oxidation and reduction of the same aldehyde
B. Oxidation of aldehyde and reduction of ketone
C. Oxidation of alcohol to aldehyde
D. Formation of a trimer

Answer: A

One molecule of aldehyde is reduced to alcohol, another oxidized to acid.

15What is the product of the reaction of Acetaldehyde with an excess of Ethanol in the presence of dry HCl?

A. Hemi-acetal
B. 1,1-Diethoxyethane (Acetal)
C. Ethyl acetate
D. Diethyl ether

Answer: B

Acetaldehyde reacts with 2 equivalents of ethanol to form acetal (diethyl acetal).

16Which amine derivative reacts with Acetone to form a product that can be used for the identification of the carbonyl group via melting point analysis?

A. NH₃
B. 2,4-Dinitrophenylhydrazine
C. Hydrazine
D. Ethylamine

Answer: B

2,4-DNPH gives crystalline derivatives with sharp melting points, used for identification.

17The reaction: R-CHO + NH₂-NH-CONH₂ → Product. The product is a:

A. Hydrazone
B. Semicarbazone
C. Oxime
D. Imine

Answer: B. Semicarbazone

Semicarbazide (NH₂NHCONH₂) gives semicarbazones with aldehydes/ketones.

18In the formation of an Oxime, the pH is carefully controlled (approx. 4.5). Why?

A. To keep the amine in its protonated form
B. To prevent the protonation of the carbonyl oxygen
C. To balance the nucleophilicity of the amine and the electrophilicity of the carbonyl
D. To speed up the elimination of CO₂

Answer: C

At pH ~4.5, the concentration of free NH₂ is sufficient for nucleophilic attack, but not too high to cause side reactions.

19Acetone reacts with Iodine in the presence of NaOH to give Iodoform and:

A. Sodium acetate
B. Sodium propionate
C. Sodium formate
D. Methanol

Answer: A. Sodium acetate

CH₃COCH₃ + 3I₂ + 4NaOH → CHI₃ + CH₃COONa + 3NaI + 3H₂O.

20Clemmensen reduction of 2-Pentanone yields:

A. n-Pentane
B. Pentan-2-ol
C. Pentan-1-ol
D. Propanoic acid

Answer: A. n-Pentane

2-Pentanone reduced to n-pentane.

21Wolff-Kishner reduction is preferred over Clemmensen reduction for compounds that are:

A. Acid-sensitive
B. Base-sensitive
C. Highly volatile
D. Saturated

Answer: A

Clemmensen uses strong acid (HCl), so acid-sensitive groups may be affected; Wolff-Kishner uses base, so better for acid-sensitive compounds.

22The oxidation of Pentan-2-one with K₂Cr₂O₇/H₂SO₄ follows Popoff's rule. The products are:

A. Ethanoic acid and Propanoic acid
B. Methanoic acid and Butanoic acid
C. Two moles of Propanoic acid
D. Ethanoic acid and Butanoic acid

Answer: A

Pentan-2-one (CH₃COCH₂CH₂CH₃) cleaves to give acetic acid (C2) and propionic acid (C3).

23Reduction of Acetone with Magnesium amalgam and water (Mg-Hg/H₂O) yields:

A. Isopropanol
B. Pinacol (2,3-dimethyl-2,3-butanediol)
C. Propane
D. Propene

Answer: B

Mg-Hg reductive coupling gives pinacol (pinacol formation).

24Which of the following reagents is used to distinguish between Pentan-2-one and Pentan-3-one?

A. 2,4-DNPH
B. NaHSO₃
C. I₂ / NaOH
D. Tollen's reagent

Answer: C

Pentan-2-one is a methyl ketone, gives iodoform test; pentan-3-one does not.

25Formaldehyde on treatment with Conc. NaOH gives Methanol and Sodium Formate. This is an example of:

A. Nucleophilic substitution
B. Internal redox (Disproportionation)
C. Electrophilic addition
D. Molecular rearrangement

Answer: B

Cannizzaro reaction is a disproportionation (internal redox).

26In the reaction of a ketone with PCl₅, the Oxygen is replaced by two Chlorine atoms to form:

A. Gem-dichloride
B. Vic-dichloride
C. Alkyl chloride
D. Acyl chloride

Answer: A. Gem-dichloride

R₂C=O + PCl₅ → R₂CCl₂ + POCl₃.

27Which of the following is used as a hypnotic drug under the name 'Chloral Hydrate'?

A. CCl₃CHO·H₂O
B. CHCl₃
C. CH₃CHO·H₂O
D. CCl₄

Answer: A

Chloral (CCl₃CHO) forms a stable hydrate, used as a sedative.

28Acetaldehyde on polymerization in the presence of Conc. H₂SO₄ at room temperature forms:

A. Paraldehyde
B. Metaldehyde
C. Formalin
D. Bakelite

Answer: A. Paraldehyde

At room temperature, acetaldehyde gives paraldehyde (cyclic trimer). At low temperature, metaldehyde (tetramer).

29Which of the following will react with NaHSO₃ but not with Tollen's reagent?

A. Ethanal
B. Acetone
C. Benzaldehyde
D. Formaldehyde

Answer: B. Acetone

NaHSO₃ adds to aldehydes and methyl ketones; Tollen's reacts only with aldehydes. Acetone (methyl ketone) gives NaHSO₃ adduct but no Tollen's.

30The boiling point of Propanal (59°C) is higher than that of n-Butane (0°C) because of:

A. Hydrogen bonding
B. Permanent dipole-dipole attractions
C. Higher molecular weight
D. Resonance stabilization

Answer: B

Propanal has a polar C=O, giving dipole-dipole interactions; n-butane has only London forces.

31Sodium borohydride (NaBH₄) is a selective reducing agent. It reduces:

A. >C=O but not -COOH or -COOR
B. -COOH but not >C=O
C. C=C double bonds
D. Both A and C

Answer: A

NaBH₄ reduces aldehydes and ketones, but not esters or carboxylic acids under normal conditions.

32The product formed when Propanone reacts with Iodine and NaOH is CHI₃. What is the other organic product?

A. Sodium acetate
B. Sodium propionate
C. Sodium formate
D. Iodo-acetone

Answer: A. Sodium acetate

Acetone gives sodium acetate (CH₃COONa).

33During the Aldol condensation of two different aldehydes (Cross-Aldol), how many total possible products can be formed?

A. 2
B. 4
C. 1
D. 3

Answer: B. 4

If both have α-hydrogens, four products: two self-condensation and two cross-condensation (but often one cross product is major).

34Which of the following test results is WRONG for Benzaldehyde?

A. Positive Tollen's test
B. Positive Fehling's test
C. Positive 2,4-DNPH test
D. Positive Cannizzaro reaction

Answer: B

Benzaldehyde does not reduce Fehling's solution (aromatic aldehydes are not oxidized by Fehling's).

35The reaction of Acetaldehyde with HCN followed by acid hydrolysis yields:

A. Lactic acid (2-hydroxypropanoic acid)
B. Glycolic acid
C. Tartaric acid
D. Propanoic acid

Answer: A

Cyanohydrin hydrolysis gives α-hydroxy acid.

36Which of the following is most acidic?

A. CH₃CHO
B. CH₃COCH₃
C. CH₂(CHO)₂ (Malonaldehyde)
D. HCHO

Answer: C

Malonaldehyde has two aldehyde groups, and the α-hydrogens are flanked by two electron-withdrawing groups, making them more acidic.

37In the Wittig reaction, a carbonyl compound is converted into:

A. An alcohol
B. An alkene
C. An alkane
D. An acid

Answer: B. An alkene

Wittig reaction: carbonyl + phosphonium ylide → alkene + phosphine oxide.

38Formaldehyde reacts with Ammonia (NH₃) to form:

A. Formaldehyde ammonia (Hexamethylenetetramine / Urotropine)
B. Acetaldehyde ammonia
C. Formamide
D. Methylamine

Answer: A

6 HCHO + 4 NH₃ → (CH₂)₆N₄ + 6 H₂O (hexamine).

39Which of the following is a trimer of Methanal?

A. Paraformaldehyde
B. Trioxane (Metaformaldehyde)
C. Paraldehyde
D. Metaldehyde

Answer: B. Trioxane

Trioxane is the cyclic trimer of formaldehyde.

40Bakelite is formed by the condensation of Formaldehyde with:

A. Phenol
B. Urea
C. Melamine
D. Benzene

Answer: A. Phenol

Phenol + formaldehyde gives Bakelite.

41The IUPAC name of the compound CH₃-CH(OH)-CH₂-CHO is:

A. 3-Hydroxybutanal
B. 2-Hydroxybutanal
C. 3-Hydroxybutane
D. Aldol

Answer: A

Four-carbon chain with aldehyde at C1 and OH at C3 → 3-hydroxybutanal.

42Which of the following reagents is used in the Clemmensen reduction?

A. NH₂NH₂ / KOH
B. Zn(Hg) / Conc. HCl
C. LiAlH₄
D. H₂ / Ni

Answer: B

Zn-Hg/HCl.

43Which of the following will give a positive Iodoform test and also react with Tollen's reagent?

A. Acetone
B. Acetaldehyde
C. Ethanol
D. Formaldehyde

Answer: B

Acetaldehyde has CH₃CO- group (iodoform) and aldehyde (Tollen's).

44Acetaldehyde reacts with PCl₅ to give:

A. Ethyl chloride
B. Ethylene dichloride
C. Ethylidene chloride (1,1-dichloroethane)
D. Chloroform

Answer: C

CH₃CHO + PCl₅ → CH₃CHCl₂ + POCl₃.

45The reaction of Acetone with CH₃MgI followed by hydrolysis gives:

A. Isopropyl alcohol
B. n-Propyl alcohol
C. tert-Butyl alcohol
D. sec-Butyl alcohol

Answer: C. tert-Butyl alcohol

Acetone + RMgX → tertiary alcohol after hydrolysis.

46In Popoff's Rule, the carbonyl group of an unsymmetrical ketone stays with the:

A. Smaller alkyl group
B. Larger alkyl group
C. Group containing a branch
D. Does not depend on the group size

Answer: A

Popoff's rule: the carbonyl stays with the smaller alkyl group.

47Fehling's solution 'A' consists of:

A. Aqueous copper sulfate
B. Alkaline sodium potassium tartrate (Rochelle salt)
C. Silver nitrate in ammonia
D. Sodium carbonate

Answer: A

Fehling's A is CuSO₄ solution; Fehling's B is alkaline Rochelle salt.

48Which of the following is used in the silvering of mirrors?

A. Methanal
B. Ethanal
C. Propanone
D. Both A and B (Methanal is preferred industrially)

Answer: D

Both formaldehyde and acetaldehyde reduce Tollen's reagent; formaldehyde is often used industrially.

49Chloral hydrate is used as:

A. A sedative/hypnotic
B. An antiseptic
C. A fungicide
D. An explosive

Answer: A

Chloral hydrate (CCl₃CH(OH)₂) is a sedative.

50The reduction of an aldehyde with NaBH₄ is an example of:

A. Nucleophilic addition
B. Electrophilic addition
C. Free radical reaction
D. Hydride transfer (a form of nucleophilic addition)

Answer: D

Hydride (H⁻) acts as a nucleophile, adding to the carbonyl carbon.

✅Practice MCQs — Test 3

🧪 Exam-Level Questions

50 MCQs

1Which of the following compounds exhibits the highest percentage of enol content at equilibrium?

A. Propanone
B. Acetaldehyde
C. Pentane-2,4-dione (Acetylacetone)
D. Cyclohexanone

Answer: C

Acetylacetone has about 76% enol due to intramolecular H-bonding and conjugation.

2The C=O stretching frequency in the IR spectrum of aldehydes and ketones typically falls in the range of 1680-1750 cm⁻¹. Conjugation of the carbonyl group with a carbon-carbon double bond will:

A. Increase the stretching frequency
B. Decrease the stretching frequency
C. Have no effect on the stretching frequency
D. Shift the absorption to the UV region

Answer: B

Conjugation reduces the C=O bond order, lowering the stretching frequency.

3Arrange the following compounds in decreasing order of their electrophilic character at the carbonyl carbon: I. Formaldehyde, II. Acetaldehyde, III. Acetone, IV. Di-tert-butyl ketone

A. I > II > III > IV
B. IV > III > II > I
C. I > III > II > IV
D. II > I > III > IV

Answer: A

Electron-donating alkyl groups decrease electrophilicity; steric hindrance also matters.

4When Acetone is treated with an excess of D₂O in the presence of a catalytic amount of OD⁻, what is the final product?

A. CD₃-CO-CH₃
B. CH₃-CD₂-CH₃
C. CD₃-CO-CD₃
D. No reaction occurs

Answer: C

Base-catalyzed enolization exchanges all α-hydrogens with deuterium.

5In the structure of Benzaldehyde, the carbonyl group is:

A. Activating and ortho/para-directing
B. Deactivating and ortho/para-directing
C. Activating and meta-directing
D. Deactivating and meta-directing

Answer: D

The -CHO group is electron-withdrawing by both -I and -M effects, deactivating and meta-directing.

6The stability of the hydrate (gem-diol) of Chloral (CCl₃CHO·H₂O) is exceptionally high compared to the hydrate of acetaldehyde. This is primarily due to:

A. Inductive effect of chlorine atoms increasing the electrophilicity of the carbonyl carbon
B. Strong intermolecular hydrogen bonding
C. Strong intramolecular hydrogen bonding between -OH and -Cl groups
D. Steric hindrance preventing dehydration

Answer: A

Electron-withdrawing CCl₃ group makes carbonyl more electrophilic, shifting equilibrium toward hydrate.

7Which of the following molecules has a net dipole moment of zero?

A. Formaldehyde
B. Acetone
C. p-Benzoquinone
D. Cyclohexanone

Answer: C

p-Benzoquinone is symmetrical, dipoles cancel.

8In comparing the C=O bond length of formaldehyde and the C=C bond length of ethylene, which statement is true?

A. The C=O bond is longer due to oxygen's larger atomic radius
B. The C=O bond is shorter due to the higher electronegativity of oxygen and stronger π-overlap
C. Both bond lengths are exactly equal because both are double bonds
D. The C=O bond is non-polar, making it longer

Answer: B

C=O bond is shorter (1.20 Å) than C=C (1.34 Å) due to greater electronegativity difference and better overlap.

9Which substituent on the benzene ring of Benzaldehyde will most significantly INCREASE the rate of nucleophilic addition (e.g., with HCN)?

A. -CH₃ (para)
B. -OCH₃ (para)
C. -NO₂ (para)
D. -OH (para)

Answer: C

Electron-withdrawing groups (NO₂) increase the electrophilicity of the carbonyl carbon, accelerating addition.

10Trichloroacetaldehyde (Chloral) undergoes the Cannizzaro reaction rather than the Aldol condensation when treated with concentrated base because:

A. It lacks α-hydrogens
B. The α-hydrogens are too sterically hindered
C. The base acts as a nucleophile rather than abstracting the highly acidic α-hydrogens
D. The resulting enolate would be highly unstable

Answer: A

Chloral has no α-hydrogens, so cannot form enolate; it undergoes Cannizzaro.

11Hydration of Propyne (CH₃-C≡CH) in the presence of HgSO₄ and H₂SO₄ yields:

A. Propanal
B. Propanone
C. Propan-1-ol
D. Propen-2-ol permanently

Answer: B. Propanone

Markovnikov addition gives enol that tautomerizes to acetone.

12The Wacker process converts ethene to ethanal using PdCl₂ and CuCl₂ as catalysts. In this reaction, the oxygen atom in ethanal originates from:

A. O₂ gas directly
B. H₂O (solvent/reactant)
C. CuCl₂
D. PdCl₂

Answer: B

The oxygen comes from water; PdCl₂ is reduced, then reoxidized by CuCl₂ and O₂.

13Ozonolysis of an unknown alkene yields one molecule of Acetone and one molecule of Acetaldehyde. The alkene is:

A. 2-Methyl-2-butene
B. 2-Methyl-1-butene
C. 3-Methyl-1-butene
D. 2-Pentene

Answer: A

2-Methyl-2-butene: (CH₃)₂C=CHCH₃ gives acetone and acetaldehyde.

14In the Rosenmund reduction (RCOCl + H₂ → RCHO + HCl), Barium sulfate (BaSO₄) and Quinoline are added to Palladium to:

A. Accelerate the reaction rate
B. Prevent the reduction of the aldehyde to an alcohol
C. Solubilize the acyl chloride
D. Neutralize the HCl produced

Answer: B

BaSO₄ and quinoline poison the catalyst, preventing over-reduction to alcohol.

15The Etard reaction converts Toluene to Benzaldehyde. The specific oxidizing agent and intermediate complex formed are:

A. KMnO₄, Benzoate complex
B. CrO₂Cl₂, Chromium complex
C. SeO₂, Selenate complex
D. O₃, Ozonide

Answer: B

Chromyl chloride (CrO₂Cl₂) oxidizes the methyl group to aldehyde via a chromium complex.

16Which of the following compounds CANNOT be prepared by Friedel-Crafts acylation of Benzene?

A. Acetophenone
B. Benzophenone
C. Benzaldehyde
D. p-Methylacetophenone

Answer: C

Formyl chloride (HCOCl) is unstable; Gattermann-Koch is used for benzaldehyde.

17Stephen's reaction involves the conversion of an alkyl cyanide (R-CN) to an aldehyde. The intermediate formed before hydrolysis is:

A. An amide
B. An iminium salt (Aldimine hydrochloride)
C. A primary amine
D. An oxime

Answer: B

Reduction with SnCl₂/HCl gives RCH=NH₂⁺Cl⁻, which hydrolyzes to RCHO.

18Gattermann-Koch formylation uses which of the following reagent combinations to introduce a formyl group onto a benzene ring?

A. CO + HCl + AlCl₃/CuCl
B. CHCl₃ + NaOH
C. HCN + HCl + AlCl₃
D. CrO₂Cl₂ + CS₂

Answer: A

CO and HCl in presence of AlCl₃/CuCl generate the formylating agent.

19Acid-catalyzed hydrolysis of a geminal dihalide (e.g., 2,2-Dichloropropane) predominantly yields:

A. A terminal alkyne
B. A vicinal diol
C. An aldehyde
D. A ketone

Answer: D

Gem-dihalide + H₂O → ketone (via gem-diol).

20Hydroboration-oxidation of a terminal alkyne (e.g., Propyne) yields:

A. A methyl ketone
B. An aldehyde
C. A secondary alcohol
D. A carboxylic acid

Answer: A

Anti-Markovnikov addition of water gives enol → methyl ketone (for terminal alkynes).

21The formation of Cyanohydrin from a ketone is thermodynamically favored. However, for highly sterically hindered ketones (like di-tert-butyl ketone), the equilibrium favors the reactants. This is due to:

A. The instability of the cyanide ion
B. Severe steric crowding in the sp³ hybridized tetrahedral product compared to the sp² reactant
C. The high acidity of the cyanohydrin
D. Hydrogen bonding effects

Answer: B

Tetrahedral intermediate is more crowded than planar carbonyl; hindrance shifts equilibrium back.

22When Acetaldehyde reacts with an optically active (R)-2-butanol in the presence of dry HCl to form an acetal, the reaction is:

A. Stereospecific, yielding a single chiral acetal
B. Stereoselective, yielding a racemic mixture
C. Reversible, with the equilibrium driven forward by removing water
D. Irreversible under acidic conditions

Answer: C

Acetal formation is reversible; removal of water drives equilibrium to product.

23In the reaction of Carbonyl compounds with Ammonia derivatives (NH₂-G), the reaction is strictly pH-dependent (optimal pH ~4.5). If the pH is too low (highly acidic, pH < 2):

A. The carbonyl oxygen is not sufficiently protonated
B. The ammonia derivative is completely protonated and loses its nucleophilicity
C. The leaving group capability of water is drastically reduced
D. The product undergoes rapid hydrolysis

Answer: B

At low pH, NH₂-G is protonated to NH₃⁺-G, no longer nucleophilic.

24Grignard addition to a chiral aldehyde (containing a stereocenter adjacent to the carbonyl) generally follows Cram's Rule. The resulting product is usually:

A. A racemic mixture of diastereomers
B. An unequal mixture of diastereomers (stereoselective)
C. A single enantiomer (stereospecific)
D. An optically inactive meso compound

Answer: B

The existing chiral center influences the face of attack, giving diastereomers in unequal amounts.

25Protecting a ketone during a multi-step synthesis is often achieved by converting it to a cyclic ketal using Ethylene Glycol. This protecting group is stable to:

A. Aqueous acids
B. Aqueous bases and strong nucleophiles (like Grignard reagents)
C. Both strong acids and bases
D. Lewis acids only

Answer: B

Ketals are stable under basic conditions but hydrolyzed by aqueous acid.

26The Wittig reaction involves the reaction of a ketone with an alkylidene phosphorane (ylide) to form an alkene. The key intermediate in this reaction is a 4-membered ring known as:

A. Oxaphosphetane
B. Epoxide
C. Dioxetane
D. Cyclobutanone

Answer: A

The oxaphosphetane intermediate decomposes to alkene and phosphine oxide.

27Baeyer-Villiger oxidation converts a ketone to an ester using a peroxyacid. In the oxidation of Methyl phenyl ketone (Acetophenone), which group migrates to the oxygen?

A. The methyl group, forming methyl benzoate
B. The phenyl group, forming phenyl acetate
C. Both migrate equally, forming a mixture
D. Neither migrates; an epoxide is formed

Answer: B

Phenyl group has higher migratory aptitude than methyl, so phenyl acetate is formed.

28Acetal formation is essentially a two-step process: formation of a hemiacetal, followed by conversion to an acetal. The second step proceeds via:

A. An S_N2 mechanism
B. An S_N1-like mechanism involving a resonance-stabilized oxocarbenium ion
C. A free radical mechanism
D. An E2 elimination

Answer: B

Protonation and loss of water give an oxocarbenium ion, which is attacked by alcohol.

29Which of the following compounds will form a stable cyclic hemiacetal?

A. 5-Hydroxypentanal
B. 2-Hydroxypropanal
C. 3-Hydroxybutanal
D. 4-Hydroxybutanoic acid

Answer: A

5-Hydroxypentanal forms a stable 6-membered ring hemiacetal.

30When Acetone reacts with PCl₅, the major product is 2,2-Dichloropropane. What is the by-product?

A. POCl₃
B. H₃PO₃
C. H₃PO₄
D. Cl₂

Answer: A

PCl₅ + R₂C=O → R₂CCl₂ + POCl₃.

31In a Cross-Cannizzaro reaction between Formaldehyde and Benzaldehyde in the presence of concentrated NaOH, the products are exclusively:

A. Sodium benzoate and Methanol
B. Benzyl alcohol and Sodium formate
C. Sodium benzoate and Sodium formate
D. Benzyl alcohol and Methanol

Answer: A

Formaldehyde is more reactive and is oxidized; benzaldehyde is reduced.

32In an Aldol condensation, the kinetic enolate is formed by removing the least sterically hindered α-hydrogen, while the thermodynamic enolate involves the most substituted α-carbon. Using a bulky base like LDA at -78°C favors:

A. The thermodynamic enolate
B. The kinetic enolate
C. Equal amounts of both
D. No enolate formation

Answer: B

Low temperature and bulky base favor kinetic enolate.

33The Clemmensen reduction (Zn-Hg/HCl) is NOT suitable for reducing ketones that also contain which of the following functional groups?

A. Alkyl groups
B. Acid-sensitive groups like Acetals or acid-hydrolyzable esters
C. Base-sensitive groups like Halogens
D. Aromatic rings

Answer: B

Strong acid conditions will hydrolyze acid-sensitive groups.

34If a molecule contains both an aldehyde and a ketone group, which reagent can selectively reduce the ketone while leaving the aldehyde intact?

A. NaBH₄
B. LiAlH₄
C. H₂ / Pd
D. It is virtually impossible to directly reduce a ketone without first protecting the more reactive aldehyde

Answer: D

Aldehydes are more reactive than ketones; selective reduction of ketone is difficult without protection.

35The Haloform reaction involves the base-promoted halogenation of a methyl ketone. The cleavage of the carbon-carbon bond occurs because:

A. The trihalomethyl group is a highly effective nucleophile
B. The CX₃⁻ carbanion is an excellent leaving group due to strong inductive stabilization
C. Halogens act as reducing agents
D. The base attacks the halogen directly

Answer: B

CX₃⁻ is stabilized by three halogens, making it a good leaving group.

36Popoff's rule dictates the cleavage of unsymmetrical ketones during drastic oxidation. Oxidation of Butanone yields:

A. Propanoic acid and Methanoic acid
B. Two moles of Ethanoic acid
C. Butanoic acid only
D. Propanone and CO₂

Answer: A

Butanone (CH₃COCH₂CH₃) gives acetic acid (C2) and propionic acid (C3).

37Alpha-hydroxy ketones (e.g., Acetoin) can give a positive test with Tollens' reagent, even though they are ketones. This is because:

A. The reagent is basic enough to isomerize the α-hydroxy ketone to an aldehyde via an enediol intermediate
B. Tollens' reagent directly oxidizes all secondary alcohols
C. The silver ion acts as a strong Lewis acid to cleave the carbon-carbon bond
D. They undergo the Cannizzaro reaction

Answer: A

Base-catalyzed tautomerization gives an aldehyde, which then reduces silver.

38Which of the following reagents specifically oxidizes the α-methylene group of a ketone to a diketone (e.g., converting cyclohexanone to cyclohexane-1,2-dione)?

A. KMnO₄ / H⁺
B. SeO₂
C. OsO₄
D. PCC

Answer: B. SeO₂

Selenium dioxide is specific for α-methylene oxidation to 1,2-diketones.

39Intramolecular Aldol condensation of Hexane-2,5-dione in the presence of dilute base yields predominantly:

A. A 4-membered ring
B. A 5-membered ring (3-Methylcyclopent-2-en-1-one)
C. A 6-membered ring
D. A 7-membered ring

Answer: B

5-Membered ring formation is kinetically favored (5-exo-trig).

40The Pinacol-Pinacolone rearrangement involves the acid-catalyzed conversion of a vicinal diol to a ketone. The driving force for the alkyl group migration is:

A. Formation of a more stable primary carbocation
B. Relief of ring strain
C. Formation of a highly stable resonance-stabilized oxonium ion (C=O double bond character)
D. Elimination of a water molecule to form an alkyne

Answer: C

Migration leads to a resonance-stabilized oxocarbenium ion, then deprotonation gives ketone.

41An unknown compound A (C₅H₁₀O) gives a positive Iodoform test and a negative Tollens' test. Upon reduction with Zn-Hg/HCl, it yields n-Pentane. Compound A is:

A. Pentanal
B. Pentan-2-one
C. Pentan-3-one
D. 3-Methylbutan-2-one

Answer: B

Methyl ketone (iodoform positive), not aldehyde (Tollens' negative), and Clemmensen gives pentane → pentan-2-one.

42A compound undergoes the Cannizzaro reaction to yield 2,2-Dimethylpropan-1-ol and Sodium 2,2-dimethylpropanoate. The starting compound is:

A. Benzaldehyde
B. 2-Methylpropanal
C. 2,2-Dimethylpropanal (Pivalaldehyde)
D. Formaldehyde

Answer: C

Only aldehydes without α-hydrogens undergo Cannizzaro; pivalaldehyde has no α-H.

43Which chemical test can accurately distinguish between Pentan-2-one and Pentan-3-one?

A. 2,4-DNPH test
B. Iodoform test
C. Tollen's test
D. Brady's test

Answer: B

Pentan-2-one is methyl ketone (iodoform positive); pentan-3-one is not.

44Reaction of Acetone with Chloroform in the presence of KOH yields Chloretone. Mechanistically, this is a:

A. Nucleophilic substitution
B. Nucleophilic addition of the trichloromethyl carbanion
C. Free radical reaction
D. Electrophilic aromatic substitution

Answer: B

CCl₃⁻ attacks carbonyl, then protonation gives trichloromethyl carbinol (chloretone).

45Acetaldehyde is reacted with dry HCl at low temperatures to form a tetramer. This compound is:

A. Paraldehyde
B. Metaldehyde
C. Urotropine
D. Trioxane

Answer: B. Metaldehyde

Metaldehyde is the tetramer of acetaldehyde (formed at low temperature).

46What is the product when Cyclopentanone reacts with Pyrrolidine (a secondary amine) in the presence of a trace of acid?

A. An imine (Schiff base)
B. An enamine
C. An oxime
D. A hydrazone

Answer: B. An enamine

Secondary amines give enamines (C=C-NR₂) with ketones.

47The Tishchenko reaction is a variation of the Cannizzaro reaction where an aldehyde with α-hydrogens is treated with Aluminum ethoxide. The product is:

A. An ester
B. A mixture of alcohol and acid
C. An aldol addition product
D. An α,β-unsaturated ketone

Answer: A. An ester

Tishchenko: 2 RCHO → RCOOCH₂R (ester).

48In the synthesis of 1°, 2°, and 3° alcohols using Grignard reagents, which carbonyl compound MUST be used to prepare a primary alcohol?

A. Any aldehyde
B. Acetaldehyde
C. Formaldehyde
D. Acetone

Answer: C. Formaldehyde

Formaldehyde gives primary alcohol (RCH₂OH).

49Compare the acidity of the α-hydrogen in Acetone (pKa ≈ 20) with the terminal hydrogen in Propyne (pKa ≈ 25). Why is the enolate more stable than the acetylide ion?

A. Carbon is more electronegative than Oxygen
B. The enolate ion delocalizes the negative charge onto a highly electronegative Oxygen atom
C. The acetylide ion has no resonance structures
D. Both B and C

Answer: D

Enolate is resonance-stabilized; acetylide has no resonance, making it less stable.

50An organic compound Z is formed by the reaction of Acetaldehyde and Formaldehyde in excess, in the presence of Ca(OH)₂ (Cross-Aldol followed by Cross-Cannizzaro). The final polyhydroxy product is:

A. Glycerol
B. Pentaerythritol
C. Sorbitol
D. Ethylene glycol

Answer: B. Pentaerythritol

Formaldehyde + acetaldehyde under basic conditions gives pentaerythritol (C(CH₂OH)₄).

📄Past Paper MCQs

📅 Actual MDCAT / NUMS Questions

50 MCQs

1The oxidation of a primary alcohol using acidified potassium dichromate primarily yields an aldehyde, but to prevent further oxidation into a carboxylic acid, the aldehyde is immediately:

UHS MDCAT 2012

A. Condensed
B. Distilled off
C. Refluxed
D. Filtered

Answer: B. Distilled off

Distillation removes the aldehyde as it forms, preventing overoxidation.

2Hydration of ethyne (C₂H₂) in the presence of 10% H₂SO₄ and 1% HgSO₄ at 80°C produces:

NUMS 2018

A. Formaldehyde
B. Acetaldehyde
C. Acetone
D. Ethanol

Answer: B. Acetaldehyde

Mercury(II) catalyzes Markovnikov addition, giving acetaldehyde.

3Dry distillation of calcium acetate alone yields:

MDCAT 2019

A. Formaldehyde
B. Acetaldehyde
C. Acetone
D. Acetic acid

Answer: C. Acetone

Calcium acetate → acetone + CaCO₃.

4Which catalyst is used in the Wacker process to convert ethene directly into ethanal using oxygen?

MDCAT 2014

A. V₂O₅
B. PdCl₂ / CuCl₂
C. Ag₂O
D. Ni / 300°C

Answer: B

Palladium(II) chloride with copper(II) chloride is the Wacker catalyst.

5When isopropyl alcohol vapors are passed over heated copper at 300°C, the process is called dehydrogenation. The product formed is:

MDCAT 2020

A. Propene
B. Propanal
C. Propanone
D. Propanoic acid

Answer: C. Propanone

Isopropyl alcohol (secondary) gives acetone.

6The industrial preparation of formaldehyde involves passing a mixture of methanol vapors and air over a heated catalyst (Fe₂O₃ + MoO₃) at:

MDCAT 2022

A. 300°C
B. 500°C
C. 700°C
D. 900°C

Answer: B. 500°C

About 500°C is used.

7Dry distillation of a mixture of Calcium formate and Calcium acetate yields primarily:

NUMS 2021

A. Methanal
B. Ethanal
C. Propanone
D. Butanone

Answer: B. Ethanal

Cross product is acetaldehyde (ethanal).

8In the carbonyl group (>C=O), the carbon atom undergoes which type of hybridization?

NUMS 2019

A. sp
B. sp²
C. sp³
D. dsp²

Answer: B. sp²

sp² hybridized.

9Ozonolysis of 2-butene followed by cleavage with Zn/H₂O yields:

NUMS 2017

A. Two molecules of Formaldehyde
B. Two molecules of Acetaldehyde
C. One molecule of Acetone and one of Formaldehyde
D. One molecule of Acetaldehyde and one of Formaldehyde

Answer: B

2-Butene (CH₃CH=CHCH₃) gives two molecules of acetaldehyde.

10Hydration of Propyne (CH₃-C≡CH) under the conditions of HgSO₄/H₂SO₄ gives:

UHS MDCAT 2018

A. Propanal
B. Propanol
C. Propanone
D. Propanoic acid

Answer: C. Propanone

Markovnikov hydration gives acetone.

11Which of the following is the correct order of reactivity towards nucleophilic addition reactions?

UHS MDCAT 2017

A. HCHO > CH₃CHO > CH₃COCH₃
B. CH₃COCH₃ > CH₃CHO > HCHO
C. CH₃CHO > HCHO > CH₃COCH₃
D. HCHO > CH₃COCH₃ > CH₃CHO

Answer: A

Formaldehyde most reactive, then acetaldehyde, then acetone.

12Ketones are comparatively less reactive than aldehydes because of:

MDCAT 2016

A. Steric hindrance of two alkyl groups
B. Electron donating (+I) effect of alkyl groups
C. Lack of α-hydrogens
D. Both A and B

Answer: D

Both steric and electronic factors reduce reactivity.

13In the base-catalyzed nucleophilic addition to a carbonyl compound, the catalyst (OH⁻) increases the reactivity of the:

NUMS 2020

A. Carbonyl carbon
B. Carbonyl oxygen
C. Nucleophile
D. Electrophile

Answer: C

Base deprotonates the nucleophile (e.g., H₂O → OH⁻).

14In the acid-catalyzed nucleophilic addition, the acid catalyst (H⁺) increases the electrophilic character of the carbonyl carbon by:

MDCAT 2018

A. Protonating the nucleophile
B. Protonating the carbonyl oxygen
C. Removing water from the system
D. Creating a carbocation

Answer: B

Protonation of oxygen makes carbon more δ⁺.

15The reaction of Hydrogen Cyanide (HCN) with acetaldehyde yields a:

UHS MDCAT 2015

A. Cyanohydrin
B. Hydrazone
C. Oxime
D. Acetal

Answer: A. Cyanohydrin

Cyanohydrin (CH₃CH(OH)CN).

16Addition of Sodium bisulfite (NaHSO₃) to carbonyl compounds yields a white crystalline precipitate. This reaction is used for the:

NUMS 2022

A. Oxidation of ketones
B. Reduction of aldehydes
C. Purification and separation of carbonyl compounds
D. Polymerization of formaldehyde

Answer: C

Purification via bisulfite adduct.

17Which reagent gives a characteristic yellow or orange precipitate with BOTH aldehydes and ketones?

MDCAT 2021

A. Tollens' Reagent
B. Fehling's Solution
C. 2,4-Dinitrophenylhydrazine (2,4-DNPH)
D. Benedict's Reagent

Answer: C

2,4-DNPH reacts with both.

18Reaction of Formaldehyde with Grignard reagent (CH₃MgI) followed by acid hydrolysis yields:

UHS MDCAT 2019

A. Ethanol (Primary alcohol)
B. Propan-2-ol (Secondary alcohol)
C. 2-Methylpropan-2-ol (Tertiary alcohol)
D. Acetaldehyde

Answer: A

HCHO + CH₃MgI → CH₃CH₂OH.

19Reaction of Acetaldehyde with Methyl magnesium iodide followed by hydrolysis yields:

NUMS 2017

A. 1-Propanol
B. 2-Propanol
C. 1-Butanol
D. 2-Methyl-2-propanol

Answer: B. 2-Propanol

CH₃CHO + CH₃MgI → CH₃CH(OH)CH₃ (isopropanol).

20Reaction of Acetone with Methyl magnesium bromide followed by hydrolysis yields:

MDCAT 2013

A. Isopropanol
B. Isobutanol
C. tert-Butyl alcohol
D. sec-Butyl alcohol

Answer: C. tert-Butyl alcohol

Acetone + CH₃MgBr → (CH₃)₃COH.

21Which of the following compounds will undergo the Aldol condensation?

MDCAT 2020

A. Formaldehyde
B. Benzaldehyde
C. Acetaldehyde
D. Trichloroacetaldehyde

Answer: C. Acetaldehyde

Acetaldehyde has α-hydrogens.

22The product formed when two molecules of acetaldehyde undergo condensation in the presence of dilute NaOH is:

NUMS 2018

A. 2-Hydroxybutanal
B. 3-Hydroxybutanal (Aldol)
C. 4-Hydroxybutanal
D. Lactic acid

Answer: B. 3-Hydroxybutanal (Aldol)

Aldol product: 3-hydroxybutanal.

23Which condition is strictly required for a carbonyl compound to undergo Cannizzaro's reaction?

UHS MDCAT 2016

A. Presence of at least one α-hydrogen
B. Absence of α-hydrogens
C. Presence of a methyl group attached to the carbonyl
D. Strong acidic medium

Answer: B. Absence of α-hydrogens

No α-hydrogens.

24When formaldehyde is treated with 50% NaOH solution, it undergoes disproportionation to form:

MDCAT 2023

A. Methanol and Sodium formate
B. Ethanol and Sodium acetate
C. Methyl acetate
D. Acetal

Answer: A

Cannizzaro: HCHO → CH₃OH + HCOONa.

25Which of the following will NOT undergo Cannizzaro reaction?

NUMS 2015

A. HCHO
B. C₆H₅CHO
C. (CH₃)₃C-CHO
D. CH₃CHO

Answer: D. CH₃CHO

Acetaldehyde has α-hydrogens, so it undergoes aldol, not Cannizzaro.

26Tollens' reagent is chemically:

NUMS 2016

A. Alkaline potassium permanganate
B. Ammoniacal silver nitrate solution
C. Ammoniacal cuprous chloride
D. Copper sulfate and sodium citrate

Answer: B

[Ag(NH₃)₂]⁺ solution.

27A silver mirror is formed on the inner walls of a test tube when Tollens' reagent is heated with:

MDCAT 2017

A. Acetone
B. Diethyl ketone
C. Acetaldehyde
D. Acetic acid

Answer: C. Acetaldehyde

Aldehydes reduce Ag⁺ to Ag.

28Fehling's solution 'A' (Aqueous CuSO₄) and 'B' (Rochelle salt + NaOH) on heating with an aliphatic aldehyde produce a brick-red precipitate of:

UHS MDCAT 2014

A. Cu metal
B. Cu₂O
C. CuO
D. CuSO₄·5H₂O

Answer: B. Cu₂O

Cuprous oxide (Cu₂O).

29Which of the following compounds will give a positive Iodoform test (yellow precipitate)?

MDCAT 2019

A. Formaldehyde
B. 3-Pentanone
C. 2-Pentanone
D. Benzaldehyde

Answer: C. 2-Pentanone

2-Pentanone is a methyl ketone.

30Which of the following sets of compounds gives a positive Iodoform test?

NUMS 2021

A. Ethanol, Acetaldehyde, Acetone, 2-Propanol
B. Methanol, Formaldehyde, Acetone, 1-Propanol
C. Ethanol, Propanal, Acetone, 2-Butanol
D. Methanol, Acetaldehyde, 3-Pentanone, 1-Butanol

Answer: A

All have CH₃CO- or CH₃CH(OH)- group.

31Vigorous oxidation of symmetrical ketones with acidified K₂Cr₂O₇ yields:

MDCAT 2015

A. A mixture of carboxylic acids
B. Only one type of carboxylic acid
C. An aldehyde
D. Esters

Answer: B

Symmetrical ketone gives two molecules of same acid.

32According to Popoff's rule, during the oxidation of unsymmetrical ketones, the carbonyl group stays with the:

NUMS 2019

A. Larger alkyl group
B. Smaller alkyl group
C. Unbranched alkyl group
D. Phenyl group

Answer: B

Smaller alkyl group.

33Benedict's solution is used primarily to detect the presence of:

UHS MDCAT 2020

A. Aliphatic aldehydes (like glucose)
B. Aromatic aldehydes
C. Aliphatic ketones
D. Phenols

Answer: A

Benedict's test for reducing sugars (aldehydes).

34To distinguish between Acetaldehyde and Acetone, which of the following tests is most suitable?

UHS MDCAT 2018

A. 2,4-DNPH test
B. Iodoform test
C. Tollens' test
D. Sodium bisulfite test

Answer: C. Tollens' test

Tollens' test: aldehyde positive, ketone negative.

35Which chemical test is used to distinguish between Pentan-2-one and Pentan-3-one?

MDCAT 2022

A. Fehling's test
B. Iodoform test
C. Tollens' test
D. Lucas test

Answer: B

Iodoform distinguishes methyl ketone.

36The yellow precipitate formed in the haloform reaction of a methyl ketone with Iodine and base is chemically:

NUMS 2015

A. CH₃I
B. CHI₃
C. CH₂I₂
D. CI₄

Answer: B. CHI₃

Iodoform (CHI₃).

37Schiff's reagent restores its magenta (pink) color when treated with:

MDCAT 2014

A. Ketones
B. Aldehydes
C. Alcohols
D. Carboxylic acids

Answer: B. Aldehydes

Aldehydes restore the color of Schiff's reagent.

38In the reaction of Acetone with I₂ and NaOH, the organic acid salt produced alongside Iodoform is:

NUMS 2020

A. Sodium formate
B. Sodium acetate
C. Sodium propionate
D. Sodium methoxide

Answer: B. Sodium acetate

CH₃COONa.

39Which of the following compounds gives a red/wine-red color with alkaline Sodium Nitroprusside solution?

UHS MDCAT 2019

A. Acetaldehyde
B. Formaldehyde
C. Acetone
D. Ethanol

Answer: C. Acetone

Ketones give red color with sodium nitroprusside in alkaline medium.

40Ketones are very resistant to mild oxidizing agents. They only undergo oxidation with strong oxidizing agents like KMnO₄/H₂SO₄ through the cleavage of:

MDCAT 2018

A. C-H bonds
B. C-C bonds
C. C-O bonds
D. O-H bonds

Answer: B. C-C bonds

Ketones are cleaved at C-C bonds adjacent to carbonyl.

41The Clemmensen reduction is used to convert the carbonyl group (>C=O) to a methylene group (-CH₂-) using:

UHS MDCAT 2017

A. Zn-Hg / HCl
B. NH₂-NH₂ / KOH
C. NaBH₄
D. LiAlH₄

Answer: A. Zn-Hg / HCl

Clemmensen reduction.

42Wolff-Kishner reduction reduces aldehydes and ketones to alkanes using:

NUMS 2018

A. Hydrazine and strong base (KOH)
B. Zinc amalgam and HCl
C. Hydrogen gas and Nickel
D. Sodium and Ethanol

Answer: A

Wolff-Kishner uses NH₂NH₂ and base.

43Reduction of Acetone with Sodium borohydride (NaBH₄) yields:

MDCAT 2020

A. Propane
B. Propan-1-ol
C. Propan-2-ol
D. Propanoic acid

Answer: C. Propan-2-ol

NaBH₄ reduces ketone to secondary alcohol.

44Reduction of Acetaldehyde with Lithium aluminum hydride (LiAlH₄) yields:

NUMS 2021

A. Ethane
B. Ethanol
C. Methanol
D. Ethene

Answer: B. Ethanol

LiAlH₄ reduces aldehyde to primary alcohol.

45What is the final product when Acetone is treated with Zinc amalgam and concentrated HCl?

MDCAT 2019

A. Propan-2-ol
B. Propane
C. Propene
D. Propanal

Answer: B. Propane

Clemmensen reduction gives propane.

46'Formalin', a strong disinfectant and biological preservative, is a mixture of:

UHS MDCAT 2016

A. 40% Formaldehyde, 8% Methanol, 52% Water
B. 100% Formaldehyde gas
C. 40% Methanol, 8% Formaldehyde, 52% Water
D. 50% Formaldehyde and 50% Ethanol

Answer: A

Formalin is about 40% HCHO with methanol as stabilizer.

47Three molecules of Acetaldehyde polymerize in the presence of a few drops of concentrated H₂SO₄ at room temperature to form a cyclic trimer called:

NUMS 2017

A. Formalin
B. Paraldehyde
C. Metaldehyde
D. Bakelite

Answer: B. Paraldehyde

Paraldehyde (cyclic trimer).

48When an aldehyde reacts with an alcohol in the presence of dry HCl gas, it forms a gem-dialkoxy compound known as an:

MDCAT 2023

A. Ester
B. Acetal
C. Ether
D. Epoxide

Answer: B. Acetal

Acetal formation.

49Bakelite is a thermosetting polymer formed by the condensation reaction of Formaldehyde with:

MDCAT 2015

A. Urea
B. Melamine
C. Phenol
D. Ethylene glycol

Answer: C. Phenol

Phenol-formaldehyde resin.

50Which of the following compounds is used as a hypnotic drug under the name 'Chloral hydrate'?

MDCAT 2012

A. CCl₃CHO·H₂O
B. CHCl₃
C. CH₃CHO·H₂O
D. HCHO·H₂O

Answer: A. CCl₃CHO·H₂O

Chloral hydrate.

🔍Direct Search Queries — Aldehydes & Ketones

Exact search terms students use on Google for this chapter. Click any to jump to the relevant section:

aldehydes and ketones MDCAT notes nomenclature of aldehydes IUPAC aldehyde vs ketone difference reactivity of aldehydes vs ketones nucleophilic addition mechanism acid base catalyzed nucleophilic addition cyanohydrin formation acetal formation mechanism Grignard reagent with aldehydes ketones Tollens test silver mirror Fehling test red precipitate 2,4-DNP test carbonyl iodoform test methyl ketones Cannizzaro reaction aldol condensation reaction Clemmensen reduction mechanism Wolff-Kishner reduction mechanism oxidation of aldehydes to acids what is an aldehyde in chemistry why are aldehydes more reactive how to distinguish aldehyde from ketone Rosenmund reduction Popoff rule ketone oxidation what is formalin aldehydes and ketones MCQs with answers aldehydes ketones MCQs pdf nucleophilic addition MCQs MDCAT past papers aldehydes ketones UHS MDCAT chemistry MCQs NUMS aldehydes ketones past papers aldehydes and ketones class 12 notes carbonyl compounds MDCAT distinguishing tests for carbonyl compounds

❔Frequently Asked Questions

What is the difference between an aldehyde and a ketone?

Why are aldehydes more reactive than ketones?

Aldehydes are more reactive for two reasons: (1) Electronic — ketones have two electron-donating alkyl groups that reduce the δ+ character of the carbonyl carbon. (2) Steric — two alkyl groups in ketones cause more hindrance for approaching nucleophiles.

What is nucleophilic addition?

Nucleophilic addition is the characteristic reaction of the carbonyl group. A nucleophile attacks the electrophilic carbon, the C=O π-bond breaks, giving a tetrahedral sp³ alkoxide intermediate that is protonated. Examples: HCN (cyanohydrin), NaHSO₃, Grignard, alcohol (acetal).

What is the Tollens' test used for?

Tollens' test (silver mirror) distinguishes aldehydes from ketones. Aldehydes reduce ammoniacal silver nitrate to metallic silver (silver mirror). Ketones do not react.

What is the Fehling's test used for?

What is the 2,4-DNP test?

What is the Iodoform test?

The iodoform test uses I₂ and NaOH to detect methyl ketones (R-CO-CH₃) and acetaldehyde. A yellow precipitate of iodoform (CHI₃) forms. It distinguishes methyl ketones from other ketones.

What is Cannizzaro's reaction?

What is Aldol condensation?

What is Clemmensen reduction?

Clemmensen reduction uses Zn-Hg/HCl to reduce C=O → CH₂. It works under acidic conditions, so acid-sensitive groups may not survive.

What is Wolff-Kishner reduction?

Wolff-Kishner reduction uses NH₂NH₂ and KOH to reduce C=O → CH₂. It works under basic conditions, so preferred for acid-sensitive compounds.

How can aldehydes be prepared?

How can ketones be prepared?

What are the products of Grignard reagent with different carbonyls?

RMgX + formaldehyde → primary alcohol. + other aldehydes → secondary alcohol. + ketones → tertiary alcohol. + CO₂ → carboxylic acid.

Why is Fehling's test negative for aromatic aldehydes?

What is the Cannizzaro reaction of benzaldehyde?

Benzaldehyde (no α-H) undergoes disproportionation: 2PhCHO + NaOH → PhCH₂OH (benzyl alcohol) + PhCOONa (sodium benzoate).

What is the Rosenmund reduction?

Rosenmund reduction: RCOCl + H₂ (Pd/BaSO₄ poisoned) → RCHO + HCl. The poisoned catalyst (BaSO₄ + quinoline) prevents over-reduction to alcohol.

What is Popoff's rule?

Popoff's rule states that during oxidation of unsymmetrical ketones, the carbonyl group stays with the smaller alkyl group. Example: butanone → ethanoic acid + propanoic acid.

How many MCQs from Aldehydes & Ketones in MDCAT?

Aldehydes and Ketones typically contribute 2–3 MCQs. High-yield because distinguishing tests (Tollens, Fehling, iodoform) are frequently repeated.

What is formalin?

Formalin is ~40% formaldehyde in water, with methanol as stabilizer. Used as disinfectant and biological preservative.

Aldehydes & Ketones — Nucleophilic Addition, Reduction & Tests

⚡Quick Answers to Common Searches

What is an aldehyde?

What is a ketone?

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Tollens' test?

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Iodoform test?

Cannizzaro's reaction?

Aldol condensation?

Clemmensen reduction?

Wolff-Kishner reduction?

Grignard reactions?

Formalin?

❓People Also Ask — Aldehydes & Ketones

📋Syllabus & Learning Outcomes

📝Full Notes — Aldehydes & Ketones

1. Nomenclature & Structure

2. Preparation of Aldehydes & Ketones

3. Reactivity of Aldehydes vs Ketones

4. Acid & Base Catalyzed Nucleophilic Addition

5. Reduction to Alcohols

6. Oxidation Reactions

High-Yield Points & Common Traps

✅Practice MCQs — Test 1

🧪 Basic Concepts

✅Practice MCQs — Test 2

🧪 Advanced Concepts

✅Practice MCQs — Test 3

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