Grignard reagent RMgBr(P) reacts with water and forms a gas (Q). One gram of Q occupies 1.4 dm 3 at STP. (P) on…

Year	2026	2025	2024	Total
Questions	14	21	11	46

Year

2026

2025

2024

Total

Questions

Solution & Explanation

Core Logic

Gas (Q) is formed when RMgBr reacts with water. Thus, Q is the alkane RH. We are given that 1.0 gm of Q occupies $1.4 ~dm³$ $1.4 \mathrm{~dm}^3$ (or $1.4 ~L$ $1.4 \mathrm{~L}$) at STP. Using molar volume ( $22.4 ~L$ $22.4 \mathrm{~L}$ at STP for 1 mole): Molar mass of Q = $(22.4)/(1.4) \times 1 = 16 g/mol$ . The alkane with molecular weight 16 is Methane ( $CH₄$ $\mathrm{CH}_4$). So, R must be the methyl group ( $CH₃-$ $\mathrm{CH}_3-$). The Grignard reagent (P) is $CH₃MgBr$ $\mathrm{CH}_3\mathrm{MgBr}$.

Step 1: Reaction with Dry Ice

Reaction of Methylmagnesium bromide with dry ice ( $CO₂$ $CO_2$):

CH₃MgBr [(ii) H₃O^+](i) CO₂ (dry ice) CH₃COOH

The final compound (Z) is Acetic Acid ( $CH₃COOH$ $\mathrm{CH}_3\mathrm{COOH}$).

Preparation of Carboxylic Acids diagram for Q75 - JEE Main 2026 Evening

Step 2: Calculate Final Mass

Molar weight of Acetic Acid ( $CH₃COOH$ $\mathrm{CH}_3\mathrm{COOH}$) = $12 + 3(1) + 12 + 16(2) + 1 = 60 g/mol$ . Weight of 0.1 mole of $CH₃COOH = 0.1 \times 60 = 6 g$ .

Pattern Recognition

When evaluating the identity of a Grignard reagent, use STP volume scaling to find the exact molar mass of its alkane derivative. $1.4 \times 16 = 22.4$ $1.4 \times 16 = 22.4$ is an extremely common dimensional hook.

Chapter Mix

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More Aldehydes, Ketones and Carboxylic Acids Previous-Year Questions — Page 9

Q jee_main_2024_30_jan_morning Preparation of Aldehydes

This reduction reaction is known as:

Preparation of Aldehydes diagram for Q62 - JEE Main 2024 Morning — The image shows the catalytic hydrogenation of benzoyl chloride to benzaldehyde in the presence of Pd-BaSO4.

A. $Rosenmund reduction$ $\text{Rosenmund reduction}$
B. $Wolff-Kishner reduction$ $\text{Wolff-Kishner reduction}$
C. $Stephen reduction$ $\text{Stephen reduction}$
D. $Etard reduction$ $\text{Etard reduction}$

Solution

Related Formula

R-COCl + H₂ Pd/BaSO₄ R-CHO + HCl

Core Logic

The reaction depicts the partial reduction of an acid chloride (benzoyl chloride) to an aldehyde (benzaldehyde) using hydrogen gas in the presence of a poisoned palladium catalyst (Pd supported on $BaSO₄$ $BaSO_4$).

Preparation of Aldehydes solution diagram for Q62 - JEE Main 2024 Morning — The image shows the catalytic hydrogenation of benzoyl chloride to benzaldehyde in the presence of Pd-BaSO4.

This specific reaction is known as the Rosenmund reduction.

Pattern Recognition

Acid Chloride + $H₂, Pd/BaSO₄$ $H_2, Pd/BaSO_4$ $arrow$ $\rightarrow$ Aldehyde is strictly the Rosenmund reduction. The $BaSO₄$ $BaSO_4$ poisons the catalyst to prevent over-reduction to an alcohol.

Chapter Mix

Class 12 Chemistry: Aldehydes, Ketones and Carboxylic Acids

Q jee_main_2024_30_jan_morning Nomenclature

Structure of 4-Methylpent-2-enal is

A. $H₂C=C(CH₃)-CH₂-C(=O)H$ $$H_2C=C(CH_3)-CH_2-C(=O)H$$
B. $CH₃-CH₂-C(CH₃)=CH-C(=O)H$ $$CH_3-CH_2-C(CH_3)=CH-C(=O)H$$
C. $CH₃-CH₂-CH=C(CH₃)-C(=O)H$ $$CH_3-CH_2-CH=C(CH_3)-C(=O)H$$
D. $CH₃-CH(CH₃)-CH=CH-C(=O)H$ $$CH_3-CH(CH_3)-CH=CH-C(=O)H$$

Solution

Core Logic

Decode the IUPAC name: 4-Methylpent-2-enal

Word root: 'pent' $arrow$ $\rightarrow$ 5 carbon principal chain.
Primary suffix: '2-en' $arrow$ $\rightarrow$ Double bond starting at carbon 2.
Secondary suffix: 'al' $arrow$ $\rightarrow$ Aldehyde group (-CHO) at carbon 1.
Substituent: '4-Methyl' $arrow$ $\rightarrow$ A methyl group (-CH3) at carbon 4.

Step 1: Drafting the structure

Numbering starts from the aldehyde carbon.

C⁵ - C⁴ - C³ = C² - C¹(=O)H

Attach the methyl at $C⁴$ $C^4$:

CH₃ - CH(CH₃) - CH = CH - CHO

This matches Option 4.

Chapter Mix

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Q jee_main_2024_30_jan_morning Preparation of Aldehydes

In the given reactions identify the reagent A and reagent B.

Preparation of Aldehydes diagram for Q73 - JEE Main 2024 Morning — The image shows the oxidation of toluene to benzaldehyde via two different pathways requiring reagents A and B.

A. $A-CrO₃, B-CrO₃$ $\text{A}-CrO_3, \text{B}-CrO_3$
B. $A-CrO₃, B-CrO₂Cl₂$ $\text{A}-CrO_3, \text{B}-CrO_2Cl_2$
C. $A-CrO₂Cl₂, B-CrO₂Cl₂$
D. $A-CrO₂Cl₂, B-CrO₃$ $\text{A}-CrO_2Cl_2, \text{B}-CrO_3$

Solution

Core Logic

Pathway 1 (Upper): Toluene is treated with Reagent 'A' and acetic anhydride $(CH₃CO)₂O$ $(CH_3CO)_2O$ to form an intermediate (benzylidene diacetate), which on hydrolysis gives benzaldehyde. The reagent used here is Chromic oxide ( $CrO₃$ $CrO_3$). Thus, A is $CrO₃$ $CrO_3$.

Pathway 2 (Lower): Toluene is treated with Reagent 'B' in $CS₂$ $CS_2$ to form a chromium complex intermediate, which on hydrolysis yields benzaldehyde. This is the Etard reaction, and the reagent used is Chromyl chloride ( $CrO₂Cl₂$ $CrO_2Cl_2$). Thus, B is $CrO₂Cl₂$ $CrO_2Cl_2$.

Preparation of Aldehydes solution diagram for Q73 - JEE Main 2024 Morning — The image shows the oxidation of toluene to benzaldehyde via two different pathways requiring reagents A and B.

Step 1: Selection

Therefore, A = $CrO₃$ $CrO_3$ and B = $CrO₂Cl₂$ $CrO_2Cl_2$.

Pattern Recognition

Etard reaction always uses Chromyl chloride ( $CrO₂Cl₂$ $CrO_2Cl_2$). Oxidation of toluene with acetic anhydride uses Chromic acid ( $CrO₃$ $CrO_3$). Both stop the oxidation at the aldehyde stage via intermediate formation.

Chapter Mix

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Q87 jee_main_2024_30_jan_morning Nucleophilic Addition Reactions

The compound formed by the reaction of ethanal with semicarbazide contains ________ number of nitrogen atoms.

Numerical Answer. Answer: 3 to 3

Solution

Related Formula

CH₃-CHO + H₂N-NH-CO-NH₂ arrow CH₃-CH=N-NH-CO-NH₂ + H₂O

Core Logic

Ethanal ( $CH₃CHO$ $CH_3CHO$) reacts with semicarbazide ( $H₂N-NH-CO-NH₂$ $H_2N-NH-CO-NH_2$) via nucleophilic addition followed by elimination of water to form a semicarbazone.

Step 1: Product Analysis

The product is Ethanal semicarbazone: $CH₃-CH=N-NH-CO-NH₂$ $CH_3-CH=N-NH-CO-NH_2$. Counting the nitrogen atoms in this structure:

The imine nitrogen ( $=N-$ $=N-$)
The amine nitrogen ( $-NH-$ $-NH-$)
The amide nitrogen ( $-NH₂$ $-NH_2$)

Total = 3 Nitrogen atoms.

Chapter Mix

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Q jee_main_2024_31_jan_evening Preparation of Aldehydes and Ketones

Identify the name reaction.

Preparation of Aldehydes and Ketones diagram for Q73 - JEE Main 2024 Evening — The image shows the conversion of benzene to benzaldehyde using CO, HCl, and Anhydrous AlCl3/CuCl.

A. $Stephen reaction$ $\text{Stephen reaction}$
B. $Etard reaction$ $\text{Etard reaction}$
C. $Gatterman-koch reaction$ $\text{Gatterman-koch reaction}$
D. $Rosenmund reduction$ $\text{Rosenmund reduction}$

Solution

Core Logic

The reaction of benzene with carbon monoxide ( $CO$ $CO$) and hydrogen chloride ( $HCl$ $HCl$) in the presence of anhydrous aluminium chloride ( $AlCl₃$ $AlCl_3$) and cuprous chloride ( $CuCl$ $CuCl$) to give benzaldehyde is known as the Gatterman-Koch reaction.

Pattern Recognition

$CO + HCl arrow$ $CO + HCl \rightarrow$ Formyl chloride intermediate (in situ) with Lewis acid $arrow$ $\rightarrow$ formylation of benzene. This is definitively the Gatterman-Koch formylation.

Chapter Mix

Class 12 Chemistry: Aldehydes, Ketones and Carboxylic Acids

Grignard reagent RMgBr(P) reacts with water and forms a gas (Q). One gram of Q occupies 1.4 dm ³$^{3}$ at STP. (P) on reaction with dry ice in dry ether followed by H₃O⁺$H_{3}O^{+}$ forms a compound (Z). 0.1 mole of (Z) will weigh ____ g. (Nearest integer)

Solution & Explanation

Core Logic

Step 1: Reaction with Dry Ice

Step 2: Calculate Final Mass

Pattern Recognition

Chapter Mix

Reference Study Guides

More Aldehydes, Ketones and Carboxylic Acids Previous-Year Questions — Page 9

Solution

Related Formula

Core Logic

Pattern Recognition

Chapter Mix

Solution

Core Logic

Step 1: Drafting the structure

Chapter Mix

Solution

Core Logic

Step 1: Selection

Pattern Recognition

Chapter Mix

Solution

Related Formula

Core Logic

Step 1: Product Analysis

Chapter Mix

Solution

Core Logic

Pattern Recognition

Chapter Mix

More Aldehydes, Ketones and Carboxylic Acids Questions — jee_main_2026_24_january_evening

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Grignard reagent RMgBr(P) reacts with water and forms a gas (Q). One gram of Q occupies 1.4 dm $³$ $^{3}$ at STP. (P) on reaction with dry ice in dry ether followed by $H₃O⁺$ $H_{3}O^{+}$ forms a compound (Z). 0.1 mole of (Z) will weigh ____ g. (Nearest integer)