CUET UG Chemistry Booster Test - 2 Structure & Preparation (Aldehydes and Ketones) -

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CUET UG Chemistry Booster Test - 2 Structure & Preparation (Aldehydes and Ketones)

⏱️ 30 Minutes

❓ 20 Questions

📌 Answers are locked once submitted — results and explanations appear at the end.

CUET UG Chemistry Booster Test - 2 Structure & Preparation (Aldehydes and Ketones)

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QUESTION 1 OF 20

Consider the geometric and structural features of the carbonyl group:
1. The central carbonyl carbon is strictly sp² hybridised.
2. The carbonyl carbon and its three directly attached atoms lie in the exact same plane.
3. The unhybridised p-orbital forms a π-bond with oxygen.
4. The oxygen atom retains two non-bonding electron pairs.

Answer Review

1 Consider the geometric and structural features of the carbonyl group:
1. The central carbonyl carbon is strictly sp² hybridised.
2. The carbonyl carbon and its three directly attached atoms lie in the exact same plane.
3. The unhybridised p-orbital forms a π-bond with oxygen.
4. The oxygen atom retains two non-bonding electron pairs.

A 1, 2, 4

B 1, 2, 3

C 1, 2, 3, 4

D 1, 3, 4

💡 Short Explanation

�� Carbonyl carbon is sp² hybridised. �� Structure is trigonal planar. �� Oxygen has two lone pairs.

✅ Correct Answer Explanation

In the carbonyl group, carbon is sp² hybridised and forms a trigonal planar structure. The carbonyl carbon and the three atoms attached to it lie in the same plane. The unhybridised p-orbital of carbon overlaps with the p-orbital of oxygen to form the π-bond. Oxygen also has two non-bonding electron pairs.

❓ Why Other Options Are Incorrect

�� Option A → Omits correct statement 3.
�� Option B → Omits correct statement 4.
�� Option D → Omits correct statement 2.

🎯 Strategy

Used

Statement Analysis

🧠 Memory Trick

Carbonyl carbon = sp², planar, π-bond, oxygen lone pairs.

📚 Aldehydes, Ketones and Carboxylic Acids – Structure of Carbonyl Group

2 The approximate bond angle unit value expected for the trigonal coplanar structure of the carbonyl group is:

A 109.5°

B 120°

C 180°

D 90°

💡 Short Explanation

�� Carbonyl carbon is sp² hybridised. �� sp² geometry is trigonal planar. �� Bond angle is approximately 120°.

✅ Correct Answer Explanation

The carbonyl carbon has trigonal planar geometry due to sp² hybridisation. Therefore, the bond angles around the carbonyl carbon are approximately 120°.

❓ Why Other Options Are Incorrect

�� Option A → Bond angle of sp³ carbon.
�� Option C → Bond angle of linear geometry.
�� Option D → Not applicable to carbonyl geometry.

🎯 Strategy

Used

Hybridisation Recall

🧠 Memory Trick

sp² = 120°.

📚 Aldehydes, Ketones and Carboxylic Acids – Carbonyl Geometry

3 Match the orbital characteristic to its specific role in the carbonyl group:

List-I	List-II
1. sp² hybridised orbital of carbon	a. Interacts to form the π-bond
2. p-orbital of carbon	b. Forms three individual sigma bonds
3. p-orbital of oxygen	c. Contains two non-bonding electron pairs
4. Oxygen non-bonding pair	d. Overlaps laterally for π-bond formation

A 1-b, 2-a, 3-d, 4-c

B 1-a, 2-b, 3-c, 4-d

C 1-b, 2-d, 3-a, 4-c

D 1-d, 2-a, 3-b, 4-c

💡 Short Explanation

�� sp² orbitals form sigma bonds. �� Carbon p-orbital participates in π-bonding. �� Oxygen has two lone pairs.

✅ Correct Answer Explanation

The sp² hybridised orbitals of carbon form three sigma bonds. The unhybridised p-orbital of carbon interacts with the p-orbital of oxygen to form the π-bond. Oxygen also contains two non-bonding electron pairs.

❓ Why Other Options Are Incorrect

�� Options B, C and D contain incorrect orbital-role matching.

🎯 Strategy

Used

Match the Following

🧠 Memory Trick

sp² = sigma, p-orbital = pi.

📚 Aldehydes, Ketones and Carboxylic Acids – Bonding in Carbonyl Group

4 The π-electron cloud in the carbonyl bond is positioned specifically:

A Along the internuclear axis

B Above and below the plane of the carbonyl carbon and attached atoms

C Orthogonal to the p-orbitals

D Exclusively on the oxygen atom

💡 Short Explanation

�� π-bond forms by sidewise overlap. �� Electron cloud lies above and below the plane. �� It is not along the internuclear axis.

✅ Correct Answer Explanation

The π-bond in the carbonyl group forms by lateral overlap of p-orbitals of carbon and oxygen. Therefore, the π-electron cloud lies above and below the plane containing the carbonyl carbon and its attached atoms.

❓ Why Other Options Are Incorrect

�� Option A → Describes sigma bond electron density.
�� Option C → p-orbitals overlap laterally, not orthogonally.
�� Option D → π-electrons are shared between carbon and oxygen.

🎯 Strategy

Used

Bonding Concept Recall

🧠 Memory Trick

π-cloud stays above and below the plane.

📚 Aldehydes, Ketones and Carboxylic Acids – π-Bonding in Carbonyl Group

5 Select the accurate statements regarding carbonyl group polarity:
1. The carbon-oxygen double bond is polarised due to higher electronegativity of oxygen.
2. The carbonyl carbon acts as an electrophilic Lewis acid centre.
3. The carbonyl oxygen acts as a nucleophilic Lewis base centre.
4. Carbonyl compounds are less polar than standard ethers.

A 1, 2, 3

B 2, 3, 4

C 1, 3, 4

D 1, 2, 4

💡 Short Explanation

�� Oxygen attracts electron density. �� Carbonyl carbon becomes electrophilic. �� Oxygen behaves as Lewis base.

✅ Correct Answer Explanation

The C=O bond is polar because oxygen is more electronegative than carbon. As a result, carbon gets a partial positive charge and acts as an electrophilic Lewis acid centre, while oxygen gets a partial negative charge and acts as a nucleophilic Lewis base centre.

❓ Why Other Options Are Incorrect

�� Statement 4 is incorrect because carbonyl compounds are significantly polar.
�� Options B, C and D include statement 4.

🎯 Strategy

Used

Statement Analysis

🧠 Memory Trick

Cδ⁺ = acid, Oδ⁻ = base.

📚 Aldehydes, Ketones and Carboxylic Acids – Polarity of Carbonyl Group

6 Arrange the following compounds in increasing order of their typical boiling points, reflecting their polarity for similar molecular mass:
(A) n-Butane
(B) Acetone
(C) Propanal
(D) Methoxyethane

A (A), (D), (C), (B)

B (B), (C), (D), (A)

C (A), (C), (B), (D)

D (D), (C), (B), (A)

💡 Short Explanation

�� n-Butane is least polar. �� Ether has moderate polarity. �� Carbonyl compounds are more polar. �� Acetone has the highest boiling point among these.

✅ Correct Answer Explanation

For compounds of similar molecular mass, boiling point generally increases with polarity and strength of intermolecular forces. n-Butane is non-polar, methoxyethane is moderately polar, propanal is a polar aldehyde, and acetone is a polar ketone with stronger dipole-dipole interactions. Increasing order: n-Butane < Methoxyethane < Propanal < Acetone Therefore: (A), (D), (C), (B)

❓ Why Other Options Are Incorrect

�� Options B, C and D do not follow the correct polarity-based boiling point trend.

🎯 Strategy

Used

Ordering

🧠 Memory Trick

Alkane < Ether < Aldehyde < Ketone.

📚 Aldehydes, Ketones and Carboxylic Acids – Physical Properties of Carbonyl Compounds

7 The high polarity of the carbonyl group is supported theoretically by resonance involving a neutral structure and a:

A Triplet structure

B Dipolar structure

C Non-polar structure

D Tetrahedral structure

💡 Short Explanation

�� Carbonyl group shows resonance. �� One contributor is neutral. �� The other contributor is dipolar.

✅ Correct Answer Explanation

The polarity of the carbonyl group is explained using resonance between a neutral structure and a dipolar structure. In the dipolar form, carbon bears a positive charge and oxygen bears a negative charge.

❓ Why Other Options Are Incorrect

�� Option A → Triplet structure is not involved.
�� Option C → Does not explain polarity.
�� Option D → Carbonyl carbon is trigonal planar, not tetrahedral.

🎯 Strategy

Used

Concept Recall

🧠 Memory Trick

Carbonyl polarity = Neutral + Dipolar resonance.

📚 Aldehydes, Ketones and Carboxylic Acids – Resonance in Carbonyl Group

8 Evaluate the statements regarding the resonance characteristics of the carbonyl group:
1. It involves the shifting of π-electrons toward oxygen.
2. The dipolar structure has a formal positive charge on the carbon atom.
3. Resonance provides a clear theoretical basis for the high polarity of the group.
4. The neutral structure involves a single bond between carbon and oxygen.

A 1, 2, 3

B 2, 3, 4

C 1, 3, 4

D 1, 2, 4

💡 Short Explanation

�� π-electrons shift toward oxygen. �� Carbon becomes positively charged in dipolar form. �� This explains polarity.

✅ Correct Answer Explanation

In the carbonyl group, π-electrons are drawn toward the more electronegative oxygen atom. This produces a dipolar resonance structure in which carbon has a positive charge and oxygen has a negative charge. These resonance contributors explain the high polarity of the carbonyl group. Statement 4 is incorrect because the neutral structure contains a carbon-oxygen double bond.

❓ Why Other Options Are Incorrect

�� Statement 4 is incorrect.
�� Options B, C and D include statement 4.

🎯 Strategy

Used

Statement Analysis

🧠 Memory Trick

Neutral C=O, dipolar C⁺–O⁻.

📚 Aldehydes, Ketones and Carboxylic Acids – Resonance of Carbonyl Group

9 The chemical conversion of primary alcohols to aldehydes using oxidising agents like CrO₃ is classified as:

A Electrophilic substitution

B Controlled Oxidation

C Nucleophilic addition

D Dehydration

💡 Short Explanation

�� Primary alcohol loses hydrogen. �� Aldehyde is formed. �� Oxidising agent is used.

✅ Correct Answer Explanation

Primary alcohols can be converted into aldehydes by controlled oxidation using reagents such as CrO₃ under suitable conditions. The oxidation must be controlled to prevent further oxidation to carboxylic acids.

❓ Why Other Options Are Incorrect

�� Option A → Not an electrophilic substitution reaction.
�� Option C → Carbonyl compounds undergo nucleophilic addition, but this is preparation.
�� Option D → Dehydration removes water to form alkenes or ethers.

🎯 Strategy

Used

Reaction Type Identification

🧠 Memory Trick

Primary alcohol → Aldehyde = Controlled oxidation.

📚 Aldehydes, Ketones and Carboxylic Acids – Preparation from Alcohols

10 Identify the correct IUPAC name of the secondary alcohol that is oxidised to synthetically form propan-2-one:

A Propan-1-ol

B Propan-2-ol

C Butan-2-ol

D Ethanol

💡 Short Explanation

�� Secondary alcohols oxidise to ketones. �� Propan-2-ol gives propan-2-one. �� Propan-2-one is acetone.

✅ Correct Answer Explanation

Propan-2-one is formed by oxidation of the corresponding secondary alcohol, propan-2-ol. During oxidation, the –OH group-bearing carbon becomes the carbonyl carbon.

❓ Why Other Options Are Incorrect

�� Option A → Primary alcohol; gives propanal or propanoic acid.
�� Option C → Gives butan-2-one.
�� Option D → Primary alcohol; gives ethanal or ethanoic acid.

🎯 Strategy

Used

Product-Precursor Mapping

🧠 Memory Trick

Propan-2-ol → Propan-2-one.

📚 Aldehydes, Ketones and Carboxylic Acids – Oxidation of Alcohols

11 Why is the catalytic dehydrogenation method particularly well-suited for industrial applications?

A It efficiently processes solid alcohols.

B It is highly suitable for processing volatile alcohols over heavy metal catalysts.

C It exclusively reacts with tertiary alcohols.

D It completely bypasses the need for metal catalysts.

💡 Short Explanation

�� Alcohol vapours are passed over catalysts. �� Heavy metal catalysts like Cu or Ag are used. �� Suitable for industrial-scale preparation.

✅ Correct Answer Explanation

Catalytic dehydrogenation is industrially useful because vapours of volatile alcohols can be passed over heated heavy metal catalysts such as copper or silver to produce aldehydes or ketones efficiently.

❓ Why Other Options Are Incorrect

�� Option A → The method uses vapour-phase alcohols, not solid alcohols.
�� Option C → It is not exclusive to tertiary alcohols.
�� Option D → Metal catalysts are required.

🎯 Strategy

Used

Application-Based Reasoning

🧠 Memory Trick

Vapour alcohol + Cu/Ag = Industrial dehydrogenation.

📚 Aldehydes, Ketones and Carboxylic Acids – Catalytic Dehydrogenation

12 When secondary alcohol vapours are passed directly over a heated copper catalyst, the resulting product is predictably a:

A Primary alcohol

B Corresponding aldehyde

C Corresponding ketone

D Carboxylic acid

💡 Short Explanation

�� Secondary alcohols dehydrogenate to ketones. �� Copper catalyst removes hydrogen. �� Carbonyl compound is formed.

✅ Correct Answer Explanation

When secondary alcohol vapours are passed over heated copper, dehydrogenation occurs. Secondary alcohols lose hydrogen to form the corresponding ketones.

❓ Why Other Options Are Incorrect

�� Option A → Reactant class, not product.
�� Option B → Primary alcohols give aldehydes.
�� Option D → Carboxylic acids are not formed by simple dehydrogenation.

🎯 Strategy

Used

Product Prediction

🧠 Memory Trick

2° alcohol → Ketone.

📚 Aldehydes, Ketones and Carboxylic Acids – Dehydrogenation of Alcohols

13 The specific synthetic process involving the initial cleavage of a C=C bond using ozone and subsequent reaction with zinc dust to form carbonyl compounds is known as:

A Dehydrogenation

B Ozonolysis

C Hydration

D Etard reaction

💡 Short Explanation

�� Ozone attacks alkene double bond. �� Zn/H₂O gives carbonyl products. �� Reaction is called ozonolysis.

✅ Correct Answer Explanation

Ozonolysis is the cleavage of carbon-carbon double bonds by ozone, followed by reductive workup using zinc dust and water. It produces aldehydes and/or ketones.

❓ Why Other Options Are Incorrect

�� Option A → Removal of hydrogen from alcohols.
�� Option C → Addition of water.
�� Option D → Oxidation of aromatic methyl group.

🎯 Strategy

Used

Reaction Recognition

🧠 Memory Trick

O₃ cuts C=C.

📚 Aldehydes, Ketones and Carboxylic Acids – Preparation from Hydrocarbons

14 Which specific alkyne, when undergoing standard hydration with Hg²⁺ and H₂SO₄, uniquely yields an aldehyde instead of a ketone?

A Propyne

B But-1-yne

C Ethyne

D But-2-yne

💡 Short Explanation

�� Hydration of ethyne forms vinyl alcohol first. �� It tautomerises to ethanal. �� Product is acetaldehyde.

✅ Correct Answer Explanation

Hydration of ethyne in the presence of Hg²⁺ and H₂SO₄ gives vinyl alcohol initially. This unstable enol tautomerises to ethanal, commonly known as acetaldehyde. Other alkynes generally give ketones.

❓ Why Other Options Are Incorrect

�� Option A → Propyne gives acetone.
�� Option B → But-1-yne gives butan-2-one.
�� Option D → But-2-yne gives butan-2-one.

🎯 Strategy

Used

Exception Identification

🧠 Memory Trick

Ethyne alone gives aldehyde.

📚 Aldehydes, Ketones and Carboxylic Acids – Hydration of Alkynes

15 Identify the precise name of the catalyst mixture used to prevent over-reduction of acyl chlorides in the Rosenmund reduction:

A Palladium on barium sulphate

B Chromyl chloride

C Stannous chloride

D Cuprous chloride

💡 Short Explanation

�� Rosenmund reduction uses Pd/BaSO₄. �� Catalyst is poisoned. �� It prevents further reduction.

✅ Correct Answer Explanation

In Rosenmund reduction, acyl chlorides are reduced to aldehydes using hydrogen gas over palladium deposited on barium sulphate. The catalyst is poisoned to stop the reaction at the aldehyde stage.

❓ Why Other Options Are Incorrect

�� Option B → Used in Etard reaction.
�� Option C → Used in Stephen reaction.
�� Option D → Used in Gatterman-Koch reaction.

🎯 Strategy

Used

Named Reaction Recall

🧠 Memory Trick

Rosenmund = Pd/BaSO₄.

📚 Aldehydes, Ketones and Carboxylic Acids – Rosenmund Reduction

16 Correctly match the specific reagent with its corresponding chemical reaction:

List-I	List-II
1. Pd/BaSO₄	a. Selectively reduces nitriles and esters directly to aldehydes
2. SnCl₂ in HCl	b. Executes the Rosenmund reduction of acyl chlorides
3. DIBAL-H	c. Performs the Stephen reaction of nitriles

A 1-b, 2-c, 3-a

B 1-a, 2-b, 3-c

C 1-c, 2-a, 3-b

D 1-b, 2-a, 3-c

💡 Short Explanation

�� Pd/BaSO₄ → Rosenmund reduction. �� SnCl₂/HCl → Stephen reaction. �� DIBAL-H → Selective reduction to aldehydes.

✅ Correct Answer Explanation

List-I — List-II Pd/BaSO₄ — Executes the Rosenmund reduction of acyl chlorides SnCl₂ in HCl — Performs the Stephen reaction of nitriles DIBAL-H — Selectively reduces nitriles and esters to aldehydes Hence the correct matching is: 1-b, 2-c, 3-a

❓ Why Other Options Are Incorrect

�� Options B, C and D contain incorrect reagent-reaction pairings.

🎯 Strategy

Used

Match the Following

🧠 Memory Trick

DIBAL-H = Aldehyde formation

📚 Aldehydes, Ketones and Carboxylic Acids – Preparation of Aldehydes

17 Based carefully on the passage, what specific intermediate prevents the further oxidation of toluene directly to benzoic acid in the Etard reaction?

A Benzylidene diacetate

B Chromium complex

C Benzal chloride

D Acyl chloride

💡 Short Explanation

�� CrO₂Cl₂ forms a chromium complex. �� Hydrolysis converts it to benzaldehyde. �� Prevents oxidation to benzoic acid.

✅ Correct Answer Explanation

In the Etard reaction, chromyl chloride oxidises the methyl group of toluene to form a chromium complex. Hydrolysis of this intermediate yields benzaldehyde, thereby stopping oxidation at the aldehyde stage.

❓ Why Other Options Are Incorrect

�� Option A → Not the intermediate described.
�� Option C → Different compound.
�� Option D → Not formed in the Etard reaction.

🎯 Strategy

Used

Passage-Based Reasoning

🧠 Memory Trick

CrO₂Cl₂ → Chromium Complex → Benzaldehyde.

📚 Aldehydes, Ketones and Carboxylic Acids – Etard Reaction

18 According strictly to the provided text passage, the complete transformation of toluene to benzaldehyde using CrO₂Cl₂ is explicitly named the:

A Gatterman-Koch reaction

B Friedel-Crafts acylation

C Rosenmund reduction

D Etard reaction

💡 Short Explanation

�� Uses chromyl chloride. �� Converts side-chain methyl group to aldehyde. �� Named Etard reaction.

✅ Correct Answer Explanation

The oxidation of toluene using chromyl chloride followed by hydrolysis to obtain benzaldehyde is known as the Etard reaction.

❓ Why Other Options Are Incorrect

�� Option A → Formylation of benzene.
�� Option B → Ketone preparation.
�� Option C → Acyl chloride reduction.

🎯 Strategy

Used

Named Reaction Recall

🧠 Memory Trick

CrO₂Cl₂ = Etard.

📚 Aldehydes, Ketones and Carboxylic Acids – Preparation of Aromatic Aldehydes

19 The preparation of dialkylcadmium involves the reaction of cadmium chloride with:

A Acyl chloride

B Grignard reagent

C Benzene

D Carbon monoxide

💡 Short Explanation

�� Cadmium chloride reacts with Grignard reagent. �� Produces dialkylcadmium. �� Used for ketone preparation.

✅ Correct Answer Explanation

Dialkylcadmium compounds are prepared by reacting cadmium chloride (CdCl₂) with a Grignard reagent (RMgX). These dialkylcadmium reagents then react with acyl chlorides to form ketones.

❓ Why Other Options Are Incorrect

�� Option A → Reacts later with dialkylcadmium.
�� Option C → Not involved.
�� Option D → Used in Gatterman-Koch reaction.

🎯 Strategy

Used

Reagent Identification

🧠 Memory Trick

CdCl₂ + Grignard → Dialkylcadmium.

📚 Aldehydes, Ketones and Carboxylic Acids – Preparation of Ketones

20 Analyze the key chemical properties of Friedel-Crafts acylation for ketone preparation:
1. The reaction treats benzene or substituted benzene with an acid chloride.
2. It requires the presence of anhydrous aluminium chloride as an active catalyst.
3. It affords the corresponding ketone.
4. It primarily yields aldehydes.

A 1, 2, 3

B 2, 3, 4

C 1, 3, 4

D 1, 2, 4

💡 Short Explanation

�� Uses benzene and acid chloride. �� Requires AlCl₃ catalyst. �� Produces ketones.

✅ Correct Answer Explanation

In Friedel-Crafts acylation, benzene or substituted benzene reacts with an acid chloride in the presence of anhydrous AlCl₃. The reaction introduces an acyl group into the aromatic ring, producing the corresponding ketone.

❓ Why Other Options Are Incorrect

�� Statement 4 is incorrect because ketones, not aldehydes, are the major products.
�� Options B, C and D include statement 4.

🎯 Strategy

Used

Statement Analysis

🧠 Memory Trick

Benzene + RCOCl + AlCl₃ = Ketone.

📚 Aldehydes, Ketones and Carboxylic Acids – Friedel-Crafts Acylation for Ketone Preparation

CUET UG Chemistry Booster Test – 2 Structure & Preparation (Aldehydes and Ketones)

CUET UG Chemistry Booster Test - 2 Structure & Preparation (Aldehydes and Ketones)

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