CUET UG Chemistry Booster Test - 3 Structure & Preparation (Aldehydes and Ketones) -

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CUET UG Chemistry Booster Test - 3 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 - 3 Structure & Preparation (Aldehydes and Ketones)

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QUESTION 1 OF 20

Critically evaluate the following conceptual details regarding the sp² hybridised carbonyl carbon atom:
1. The central carbon forms three directed σ-bonds.
2. The unhybridised p-orbital is positioned perpendicular to the plane of the σ-bonds.
3. The oxygen atom possesses two non-bonding electron pairs.
4. The sp² carbon dictates that the molecule adopts a tetrahedral 3D geometry.

Answer Review

1 Critically evaluate the following conceptual details regarding the sp² hybridised carbonyl carbon atom:
1. The central carbon forms three directed σ-bonds.
2. The unhybridised p-orbital is positioned perpendicular to the plane of the σ-bonds.
3. The oxygen atom possesses two non-bonding electron pairs.
4. The sp² carbon dictates that the molecule adopts a tetrahedral 3D geometry.

A 1, 2, 3

B 2, 3, 4

C 1, 3, 4

D 1, 2, 4

💡 Short Explanation

�� Carbonyl carbon forms three σ-bonds. �� Unhybridised p-orbital forms π-bond. �� Oxygen has two lone pairs.

✅ Correct Answer Explanation

The carbonyl carbon is sp² hybridised and forms three directed sigma bonds in a trigonal planar arrangement. Its unhybridised p-orbital lies perpendicular to the plane and overlaps with the p-orbital of oxygen to form the π-bond. Oxygen also has two non-bonding electron pairs. Statement 4 is incorrect because sp² carbon has trigonal planar geometry, not tetrahedral geometry.

❓ Why Other Options Are Incorrect

�� Options B, C and D include incorrect statement 4 or omit a correct statement.

🎯 Strategy

Used

Statement Analysis

🧠 Memory Trick

sp² = planar, not tetrahedral.

📚 Aldehydes, Ketones and Carboxylic Acids – Carbonyl Structure

2 Why does the reactive carbonyl carbon structurally lie rigidly in the exact same spatial plane as the three adjacent atoms directly attached to it?

A It is due to subsequent sp³ hybridisation.

B It is a direct geometric consequence of its strictly trigonal coplanar sp² hybridised structure.

C Because the electronegative oxygen atom strongly repels the substituents out of phase.

D Due to dense intermolecular hydrogen bonding.

💡 Short Explanation

�� Carbonyl carbon is sp² hybridised. �� sp² geometry is trigonal planar. �� Attached atoms lie in the same plane.

✅ Correct Answer Explanation

The carbonyl carbon is sp² hybridised, so it forms a trigonal planar arrangement. Therefore, the carbonyl carbon and the three atoms attached to it lie in the same plane.

❓ Why Other Options Are Incorrect

�� Option A → sp³ gives tetrahedral geometry.
�� Option C → Repulsion is not the reason.
�� Option D → Hydrogen bonding does not determine carbonyl geometry.

🎯 Strategy

Used

Conceptual Reasoning

🧠 Memory Trick

sp² = same plane.

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

3 Analytically match the theoretical bonding aspects occurring within the carbonyl group structural framework:

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

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

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

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

💡 Short Explanation

�� Planar bonds are σ-bonds. �� Lateral p-orbital overlap forms π-bond. �� sp² bond angle is about 120°.

✅ Correct Answer Explanation

The sp² hybrid orbitals form three planar sigma bonds. The unhybridised p-orbitals of carbon and oxygen overlap laterally to form the π-bond. The bond angle around sp² carbon is approximately 120°, and the π-electron cloud lies above and below the plane.

❓ Why Other Options Are Incorrect

�� Options B, C and D contain incorrect matching.

🎯 Strategy

Used

Match the Following

🧠 Memory Trick

σ in plane, π above and below.

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

4 Identify the scientifically accurate theoretical descriptions regarding the active π-electron cloud of the carbonyl group:
1. It resides distinctly above and below the central trigonal coplanar plane.
2. It is formed by the lateral overlap of a p-orbital of C with a p-orbital of O.
3. It is polarised in the direction towards the more electronegative oxygen atom.
4. It strictly localises in the internuclear axis between carbon and oxygen.

A 1, 2, 3

B 1, 2, 4

C 2, 3, 4

D 1, 3, 4

💡 Short Explanation

�� π-cloud lies above and below plane. �� It forms by lateral p-p overlap. �� Oxygen pulls electron density.

✅ Correct Answer Explanation

The π-electron cloud in the carbonyl group is formed by lateral overlap of carbon and oxygen p-orbitals. It lies above and below the trigonal planar structure and is polarised toward oxygen due to oxygen's higher electronegativity. Statement 4 is incorrect because electron density along the internuclear axis corresponds to a sigma bond.

❓ Why Other Options Are Incorrect

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

🎯 Strategy

Used

Statement Analysis

🧠 Memory Trick

π = above-below, σ = axis.

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

5 The inherent electrophilic Lewis acid nature uniquely exhibited by the carbonyl carbon is fundamentally a theoretical consequence of:

A The large atomic radius size of the carbon atom.

B The lack of significant steric substituent groups.

C The higher electronegativity of oxygen actively pulling electron density away from it.

D The disruptive presence of unhybridised d-orbitals.

💡 Short Explanation

�� Oxygen is more electronegative than carbon. �� Carbon becomes partially positive. �� Carbonyl carbon acts as electrophile.

✅ Correct Answer Explanation

In the C=O bond, oxygen pulls electron density toward itself due to higher electronegativity. This gives oxygen partial negative charge and carbon partial positive charge. Hence, carbonyl carbon acts as an electrophilic Lewis acid centre.

❓ Why Other Options Are Incorrect

�� Option A → Atomic radius is not the reason.
�� Option B → Steric effect is not the main electronic cause.
�� Option D → Carbon does not use d-orbitals here.

🎯 Strategy

Used

Conceptual Reasoning

🧠 Memory Trick

Oxygen pulls, carbon becomes electrophilic.

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

6 Using conceptual depth regarding intrinsic molecular dipole interactions, strictly arrange the following compounds in decreasing order of typical boiling points for similar mass:
(A) Propan-1-ol
(B) Acetone
(C) Methoxyethane
(D) n-Butane

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

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

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

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

💡 Short Explanation

�� Alcohol has hydrogen bonding. �� Acetone has strong dipole-dipole forces. �� Ether is less polar. �� Alkane is non-polar.

✅ Correct Answer Explanation

Boiling point depends on intermolecular forces. Propan-1-ol has hydrogen bonding, so it has the highest boiling point. Acetone is strongly polar due to the carbonyl group. Methoxyethane is less polar than acetone, while n-butane has only weak dispersion forces. Decreasing order: Propan-1-ol > Acetone > Methoxyethane > n-Butane

❓ Why Other Options Are Incorrect

�� Options B, C and D do not follow intermolecular force strength.

🎯 Strategy

Used

Ordering

🧠 Memory Trick

H-bond > carbonyl dipole > ether dipole > alkane.

📚 Aldehydes, Ketones and Carboxylic Acids – Physical Properties

7 Critically analyze the theoretical resonance structures assigned to the highly polar carbonyl group:
1. The assigned neutral resonance structure maintains a standard double bond.
2. The formal dipolar structure explicitly features a positively charged electrophilic carbon atom.
3. The formal dipolar structure isolates a negative charge on oxygen.
4. The resonance does not account for the chemically substantial dipole moment observed.

A 1, 2, 3

B 2, 3, 4

C 1, 3, 4

D 1, 2, 4

💡 Short Explanation

�� Neutral form has C=O double bond. �� Dipolar form has C⁺ and O⁻. �� Resonance explains polarity.

✅ Correct Answer Explanation

The carbonyl group is represented by a neutral structure containing a C=O double bond and a dipolar structure where carbon bears a positive charge and oxygen bears a negative charge. This resonance explanation accounts for the high polarity and dipole moment of carbonyl compounds. Statement 4 is incorrect.

❓ Why Other Options Are Incorrect

�� Options B, C and D include incorrect statement 4 or omit correct statements.

🎯 Strategy

Used

Statement Analysis

🧠 Memory Trick

Carbonyl resonance: C=O ↔ C⁺–O⁻.

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

8 In the context of the carbonyl group's resonance hybrid, the existence of the dipolar structure primarily helps conceptually explain the:

A High polarity and nucleophilic nature of the carbonyl oxygen.

B Low boiling point compared to hydrocarbons.

C Exact 120° bond angles.

D sp³ hybridisation of the carbon atom.

💡 Short Explanation

�� Dipolar structure has O⁻ character. �� Oxygen becomes electron-rich. �� Carbonyl group becomes highly polar.

✅ Correct Answer Explanation

The dipolar resonance structure of the carbonyl group places a negative charge on oxygen and a positive charge on carbon. This explains the high polarity of the carbonyl bond and the nucleophilic Lewis base character of oxygen.

❓ Why Other Options Are Incorrect

�� Option B → Carbonyl compounds generally have higher boiling points than hydrocarbons of similar mass.
�� Option C → Bond angle is due to sp² hybridisation, not dipolar resonance.
�� Option D → Carbonyl carbon is sp² hybridised, not sp³.

🎯 Strategy

Used

Conceptual Reasoning

🧠 Memory Trick

O⁻ in resonance = nucleophilic oxygen.

📚 Aldehydes, Ketones and Carboxylic Acids – Carbonyl Polarity and Resonance

📄 Passage

Aldehydes and ketones are generally prepared by the controlled oxidation of primary and secondary alcohols, respectively. In chemical industry, an alternate related method is highly preferred. This specific method is known as the dehydrogenation of alcohols, which is exceptionally suitable for highly volatile alcohols and operates on a large industrial application scale. In this precise industrial method, the highly volatile alcohol vapours are carefully passed over heated heavy metal catalysts, specifically silver (Ag) or copper (Cu).

Based strictly on the passage, the industrial dehydrogenation method is exceptionally suitable for which type of reactant?

A Solid phase alcohols

B Volatile alcohols

C Aromatic hydrocarbons

D Alkyl halides

💡 Short Explanation

�� Passage directly mentions volatile alcohols. �� Vapours are passed over catalysts. �� Method is industrially suitable.

✅ Correct Answer Explanation

The passage states that dehydrogenation of alcohols is exceptionally suitable for highly volatile alcohols. These alcohol vapours are passed over heated silver or copper catalysts to produce aldehydes or ketones.

❓ Why Other Options Are Incorrect

�� Option A → Solid alcohols are not mentioned.
�� Option C → Aromatic hydrocarbons are not the reactants here.
�� Option D → Alkyl halides are unrelated.

🎯 Strategy

Used

Passage-Based Analysis

🧠 Memory Trick

Dehydrogenation works well with volatile alcohol vapours.

📚 Aldehydes, Ketones and Carboxylic Acids – Industrial Dehydrogenation

📄 Passage

Based exclusively on the passage provided, what primary starting factor explicitly dictates the choice between obtaining an aldehyde versus a ketone during catalytic dehydrogenation?

A The exact operational temperature of the solid metal catalyst

B The specific use of Ag versus the use of Cu

C Whether the volatile reactant is definitively a primary or secondary alcohol

D The external introduction of a significantly strong acidic medium

💡 Short Explanation

�� Primary alcohols give aldehydes. �� Secondary alcohols give ketones. �� Reactant class determines product type.

✅ Correct Answer Explanation

The passage states that aldehydes and ketones are prepared from primary and secondary alcohols respectively. Therefore, during catalytic dehydrogenation, whether the starting alcohol is primary or secondary determines whether the product is an aldehyde or a ketone.

❓ Why Other Options Are Incorrect

�� Option A → Temperature is not given as the deciding factor.
�� Option B → Ag or Cu acts as catalyst; product type depends on alcohol class.
�� Option D → Strong acidic medium is not involved.

🎯 Strategy

Used

Passage-Based Reasoning

🧠 Memory Trick

1° alcohol → Aldehyde; 2° alcohol → Ketone.

📚 Aldehydes, Ketones and Carboxylic Acids – Preparation from Alcohols

11 During the specific dehydrogenation of ethanol over heated Cu, what is the precise analytical role of the catalyst involved in the transformation?

A It facilitates the addition of oxygen atoms.

B It promotes the removal of hydrogen, acting as a dehydrogenating agent.

C It acts as a standard hydration agent adding water.

D It causes the cleavage of the carbon-carbon skeletal bond.

💡 Short Explanation

�� Dehydrogenation means removal of hydrogen. �� Cu helps convert ethanol to ethanal. �� No oxygen addition occurs.

✅ Correct Answer Explanation

In catalytic dehydrogenation, ethanol vapour is passed over heated copper. The catalyst promotes removal of hydrogen from ethanol, converting it into ethanal. Reaction: CH₃CH₂OH → CH₃CHO + H₂

❓ Why Other Options Are Incorrect

�� Option A → Oxygen atoms are not added.
�� Option C → Water is not added.
�� Option D → Carbon-carbon bond cleavage does not occur.

🎯 Strategy

Used

Reaction Role Analysis

🧠 Memory Trick

Dehydrogenation = Hydrogen removed.

📚 Aldehydes, Ketones and Carboxylic Acids – Dehydrogenation of Alcohols

12 The specific industrial methodology of safely passing heated alcohol vapours over solid Ag or Cu to catalytically yield distinct carbonyl compounds is fundamentally categorized chemically as:

A Reductive amination

B Nucleophilic hydrolysis

C Catalytic dehydrogenation

D Reversible esterification

💡 Short Explanation

�� Alcohol vapours are passed over Cu or Ag. �� Hydrogen is removed. �� Aldehydes or ketones are formed.

✅ Correct Answer Explanation

Passing alcohol vapours over heated copper or silver catalyst removes hydrogen from alcohols and forms carbonyl compounds. This reaction is known as catalytic dehydrogenation.

❓ Why Other Options Are Incorrect

�� Option A → Involves amine formation.
�� Option B → Involves hydrolysis by water.
�� Option D → Forms esters.

🎯 Strategy

Used

Reaction Type Identification

🧠 Memory Trick

Alcohol vapour + Cu/Ag = Dehydrogenation.

📚 Aldehydes, Ketones and Carboxylic Acids – Industrial Preparation Method

13 Strictly arrange the following experimental steps in the scientifically correct sequence for successfully preparing a ketone strictly via ozonolysis:
(A) Subsequent critical reaction with zinc dust and water to cleave the intermediate
(B) Regulated direct addition of highly reactive ozone gas
(C) Careful initial selection of an appropriately substituted alkene

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

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

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

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

💡 Short Explanation

�� Select alkene first. �� Add ozone to form ozonide. �� Use Zn/H₂O for cleavage.

✅ Correct Answer Explanation

In ozonolysis, the correct sequence is: 1. Select the appropriate alkene. 2. Add ozone to form the ozonide intermediate. 3. Treat with zinc dust and water to cleave the intermediate into carbonyl products. Therefore: (C) → (B) → (A)

❓ Why Other Options Are Incorrect

�� Options B, C and D do not follow the correct experimental order.

🎯 Strategy

Used

Ordering

🧠 Memory Trick

Alkene → Ozone → Zn/H₂O.

📚 Aldehydes, Ketones and Carboxylic Acids – Ozonolysis

14 Analytically match the specific hydrocarbon starting material condition with its expected final carbonyl product after chemical treatment:

List-I	List-II
1. Ethyne subjected to H₂O with Hg²⁺, H₂SO₄	a. Exclusively yields Ketone(s)
2. Substituted alkynes subjected to H₂O with Hg²⁺, H₂SO₄	b. Exclusively yields Acetaldehyde
3. Alkenes subjected to O₃ followed by Zn/H₂O	c. Yields Aldehydes, Ketones, or a mixture

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

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

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

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

💡 Short Explanation

�� Ethyne hydration gives acetaldehyde. �� Substituted alkynes give ketones. �� Alkene ozonolysis gives aldehydes/ketones.

✅ Correct Answer Explanation

Ethyne undergoes hydration in the presence of Hg²⁺ and H₂SO₄ to form acetaldehyde. Substituted alkynes generally give ketones under similar conditions. Alkenes on ozonolysis followed by Zn/H₂O cleavage can form aldehydes, ketones, or a mixture depending on alkene structure.

❓ Why Other Options Are Incorrect

�� Options B, C and D contain incorrect product matching.

🎯 Strategy

Used

Match the Following

🧠 Memory Trick

Ethyne → Acetaldehyde; substituted alkyne → Ketone.

📚 Aldehydes, Ketones and Carboxylic Acids – Preparation from Hydrocarbons

15 Critically analyze the chemical nuances of the Rosenmund reduction process:
1. It deliberately reduces strongly reactive acyl chlorides explicitly down to aldehydes.
2. The precise catalyst utilized is pure palladium supported on barium sulphate.
3. The process strictly requires hydrogenation.
4. It is an efficient primary way to generally prepare nitriles.

A 1, 2, 3

B 2, 3, 4

C 1, 3, 4

D 1, 2, 4

💡 Short Explanation

�� Acyl chlorides are reduced to aldehydes. �� Pd/BaSO₄ catalyst is used. �� Hydrogen gas is required.

✅ Correct Answer Explanation

Rosenmund reduction converts acyl chlorides into aldehydes by catalytic hydrogenation using palladium supported on barium sulphate. Statement 4 is incorrect because this reaction prepares aldehydes, not nitriles.

❓ Why Other Options Are Incorrect

�� Options B, C and D include incorrect statement 4 or omit correct statements.

🎯 Strategy

Used

Statement Analysis

🧠 Memory Trick

Rosenmund = Acyl chloride to aldehyde.

📚 Aldehydes, Ketones and Carboxylic Acids – Rosenmund Reduction

16 The specific chemical conversion of nitriles to imines using stannous chloride and hydrochloric acid, followed immediately by rapid hydrolysis to aldehydes, acts chemically as a:

A Selective reduction followed by hydrolysis

B Complete oxidative cleavage

C Free radical driven substitution

D Standard basic condensation

💡 Short Explanation

�� Nitrile is selectively reduced to imine. �� Hydrolysis gives aldehyde. �� This is Stephen reaction.

✅ Correct Answer Explanation

In the Stephen reaction, nitriles are selectively reduced using stannous chloride and hydrochloric acid to form imine or iminium salt intermediates. These intermediates undergo hydrolysis to produce aldehydes.

❓ Why Other Options Are Incorrect

�� Option B → It is not oxidative cleavage.
�� Option C → No free radical mechanism is involved.
�� Option D → It is not a basic condensation reaction.

🎯 Strategy

Used

Reaction Type Identification

🧠 Memory Trick

Stephen: Nitrile → Imine → Aldehyde.

📚 Aldehydes, Ketones and Carboxylic Acids – Stephen Reaction

17 The precise scientific nomenclature for the critical intermediate chemical complex safely formed in the Etard reaction, which exclusively upon hydrolysis eventually yields pure benzaldehyde, is precisely a:

A Stannous complex

B Chromium complex

C Palladium complex

D Cadmium complex

💡 Short Explanation

�� Etard reaction uses chromyl chloride. �� Chromium complex is formed. �� Hydrolysis gives benzaldehyde.

✅ Correct Answer Explanation

In the Etard reaction, chromyl chloride oxidises the methyl group of toluene and forms a chromium complex. On hydrolysis, this complex gives benzaldehyde.

❓ Why Other Options Are Incorrect

�� Option A → Related to Stephen reaction reagent.
�� Option C → Related to Rosenmund reduction catalyst.
�� Option D → Related to ketone preparation using dialkylcadmium.

🎯 Strategy

Used

Named Reaction Recall

🧠 Memory Trick

Etard = Chromium complex.

📚 Aldehydes, Ketones and Carboxylic Acids – Etard Reaction

18 In the Gattermann-Koch reaction mechanism, carbon monoxide combined with hydrogen chloride acts synthetically together in the presence of anhydrous aluminium chloride to effectively introduce which specific functional group into the benzene ring?

A Carboxyl group

B Formyl group (Aldehyde)

C Ketone group

D Acyl chloride group

💡 Short Explanation

�� Gattermann-Koch is formylation. �� Introduces –CHO group. �� Produces benzaldehyde.

✅ Correct Answer Explanation

The Gattermann-Koch reaction introduces a formyl group (–CHO) into the benzene ring using carbon monoxide and hydrogen chloride in the presence of anhydrous AlCl₃/CuCl.

❓ Why Other Options Are Incorrect

�� Option A → –COOH group is not introduced.
�� Option C → Ketone group is introduced in Friedel-Crafts acylation.
�� Option D → Acyl chloride is not the final group introduced.

🎯 Strategy

Used

Reaction Function Analysis

🧠 Memory Trick

Gattermann-Koch = Benzene to benzaldehyde.

📚 Aldehydes, Ketones and Carboxylic Acids – Gattermann-Koch Reaction

19 The chemical synthesis of ketones via dialkylcadmium strictly requires the prior preparation of dialkylcadmium through the specific reaction of a Grignard reagent with:

A Stannous chloride

B Cadmium chloride

C Chromyl chloride

D Cuprous chloride

💡 Short Explanation

�� Grignard reagent reacts with CdCl₂. �� Dialkylcadmium is formed. �� It then reacts with acyl chloride to give ketone.

✅ Correct Answer Explanation

Dialkylcadmium is prepared by reacting a Grignard reagent with cadmium chloride: 2RMgX + CdCl₂ → R₂Cd + 2MgXCl The dialkylcadmium then reacts with acyl chlorides to form ketones.

❓ Why Other Options Are Incorrect

�� Option A → Used in Stephen reaction.
�� Option C → Used in Etard reaction.
�� Option D → Used in Gattermann-Koch reaction.

🎯 Strategy

Used

Reagent Identification

🧠 Memory Trick

CdCl₂ makes dialkylcadmium.

📚 Aldehydes, Ketones and Carboxylic Acids – Ketone Preparation

20 In the IUPAC nomenclature of standard ketones, the positional numeral unit indicating the lowest possible location for the carbonyl group in an open straight carbon chain is:

A 1

B 2

C 3

D 4

💡 Short Explanation

�� Ketone carbonyl cannot be terminal. �� Lowest possible position is carbon-2. �� Carbon-1 carbonyl would be an aldehyde.

✅ Correct Answer Explanation

In open-chain ketones, the carbonyl carbon must be bonded to two carbon atoms. Therefore, it cannot be at carbon-1. The lowest possible locant for a ketone carbonyl group is carbon-2.

❓ Why Other Options Are Incorrect

�� Option A → Carbon-1 carbonyl gives aldehyde, not ketone.
�� Options C and D → Higher locants, not the lowest possible.

🎯 Strategy

Used

Nomenclature Rule Analysis

🧠 Memory Trick

Ketone starts from carbon-2.

📚 Aldehydes, Ketones and Carboxylic Acids – Ketone Nomenclature

CUET UG Chemistry Booster Test – 3 Structure & Preparation (Aldehydes and Ketones)

CUET UG Chemistry Booster Test - 3 Structure & Preparation (Aldehydes and Ketones)

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Answer Review