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Haloalkanes and Haloarenes appeared 40 times across 3 years — 4.7% of Chemistry. This question is from Ambident Nucleophiles Reactions.

Year 2026 2025 2024 Total
Questions 11 16 13 40

The products A and B in the following reactions, respectively are A A g - N O _ 2 C H _ 3 - C H _ 2 - C H _ 2 - B r A g C N B

Solution & Explanation

Core Logic

Both silver reagents exhibit significantly covalent bond characters:

  • Reaction with AgNO₂: The bond between silver and oxygen is covalent, making the lone pair on the nitrogen atom the primary nucleophilic site. Attack via nitrogen yields a nitroalkane product:
A = CH₃-CH₂-CH₂-NO₂
  • Reaction with AgCN: The covalent Ag-C bond directs the nucleophilic attack to proceed through the lone pair on nitrogen, yielding an isocyanide compound:
B = CH₃-CH₂-CH₂-NC

Hence, option (4) represents the correct combination.

Pattern Recognition

Sees: Alkyl halide reacting with covalent silver salts of ambident anions. Shortcut: Silver reagents (AgCN or AgNO₂) drive bond formatting via the nitrogen center, producing isocyanides and nitroalkanes respectively.

Chapter Mix

Class 12 Chemistry: Haloalkanes and Haloarenes

Reference Study Guides

More Haloalkanes and Haloarenes Previous-Year Questions — Page 5

Q32 jee_main_2025_07_april_evening Nucleophilic Aromatic Substitution
Match List-I with List-II.
List-I (Conversion) List-II (Reagents, Conditions used) [cite: 248, 249]
(A) Chlorobenzene arrow Phenol(I) Warm, H₂O
(B) p-Nitrochlorobenzene arrow p-Nitrophenol(II) (a) NaOH, 368 K; (b) H3O^+ (C) 2,4-Dinitrochlorobenzene arrow 2,4-Dinitrophenol(III) (a) NaOH, 443 K; (b) H₃O^+ (D) 2,4,6-Trinitrochlorobenzene arrow 2,4,6-Trinitrophenol(IV) (a) NaOH, 623 K, 300 atm; (b) H₃O^+ Choose the correct answer from the options given below:
  • A. (A)-(II), (B)-(III), (C)-(I), (D)-(IV)
  • B. (A)-(III), (B)-(IV), (C)-(II), (D)-(I)
  • C. (A)-(IV), (B)-(III), (C)-(II), (D)-(I)
  • D. (A)-(IV), (B)-(III), (C)-(I), (D)-(II)

Solution

Related Formula
Rate of SNAr ∝ Number of electron-withdrawing groups (-I, -M) at ortho/para positions
Core Logic

Aryl halides are generally unreactive towards nucleophilic substitution due to resonance stabilization of the C-Cl bond. However, the presence of strong electron-withdrawing groups (-NO₂) at ortho and para positions dramatically increases reactivity by stabilizing the intermediate carbanion:

- (A) Chlorobenzene: Needs extreme conditions: NaOH at 623 K, 300 atm (Dow's Process) arrow (IV) - (B) p-Nitrochlorobenzene: One para -NO₂ group softens required temperature to 443 K arrow (III) - (C) 2,4-Dinitrochlorobenzene: Two electron-withdrawing groups lower needed temperature further to 368 K arrow (II) - (D) 2,4,6-Trinitrochlorobenzene: Highly activated picryl chloride hydrolyzes smoothly with just warm water arrow (I)

Step 1: Final Match Alignment

Matching sequences cleanly yields: (A)-(IV), (B)-(III), (C)-(II), (D)-(I).

Pattern Recognition

The more -NO₂ groups present on the ring, the less aggressive the reagent/temperature setup required. Count -NO₂ groups: 0 arrow 623K, 1 arrow 443K, 2 arrow 368K, 3 arrow warm water.

Chapter Mix

Class 12 Chemistry: Haloalkanes and Haloarenes

Q42 jee_main_2025_07_april_evening Physical Properties of Dihalobenzenes
Given below are two statements: Statement (I):
Physical Properties of Dihalobenzenes diagram for Q42 - JEE Main 2025 Evening
The structural layouts show ortho and para halobenzene isomers (1,2-dichlorobenzene vs 1,2-dibromobenzene, and para-dibromobenzene).
is more polar than
Physical Properties of Dihalobenzenes diagram for Q42 - JEE Main 2025 Evening
The structural layouts show ortho and para halobenzene isomers (1,2-dichlorobenzene vs 1,2-dibromobenzene, and para-dibromobenzene).
. Statement (II): Boiling point of
Physical Properties of Dihalobenzenes diagram for Q42 - JEE Main 2025 Evening
The structural layouts show ortho and para halobenzene isomers (1,2-dichlorobenzene vs 1,2-dibromobenzene, and para-dibromobenzene).
is lower than the ortho-isomer, but it is more polar than the meta-isomer. In the light of the above statements, choose the most appropriate answer from the options given below:
  • A. Statement I is correct but statement II is incorrect
  • B. Statement I is incorrect but statement II is correct
  • C. Both statement I and statement II are incorrect
  • D. Both statement I and statement II are correct

Solution

Related Formula
μnet = √(μ₁² + μ₂² + 2μ₁μ₂ θ) Boiling point ∝ Dipole-dipole interactions + Van der Waals forces
Core Logic

Let's analyze the visual structures alongside their scientific orientations:

  • Statement (I) compares 1,2-dichlorobenzene and 1,2-dibromobenzene. Chlorine has a higher electronegativity than bromine, creating a larger bond dipole. The vacant d-orbital interactions do not invert this baseline dipole trend. Thus, 1,2-dichlorobenzene is more polar, making Statement I correct.
  • Statement (II) evaluates dihalobenzene isomers. For the para-isomer, individual bond dipoles are oriented at 180°, cancelling out completely:
μpara = 0

Since μmeta > 0, the para-isomer is less polar than the meta-isomer. This directly falsifies Statement II.

Step 1: Spatial Alignments

The geometric configurations map out as follows:

Physical Properties of Isomers vector diagram for Q42 - JEE Main 2025 Evening
The structural layouts show ortho and para halobenzene isomers (1,2-dichlorobenzene vs 1,2-dibromobenzene, and para-dibromobenzene).

Physical Properties of Isomers vector diagram for Q42 - JEE Main 2025 Evening
The structural layouts show ortho and para halobenzene isomers (1,2-dichlorobenzene vs 1,2-dibromobenzene, and para-dibromobenzene).

Physical Properties of Isomers vector diagram for Q42 - JEE Main 2025 Evening
The structural layouts show ortho and para halobenzene isomers (1,2-dichlorobenzene vs 1,2-dibromobenzene, and para-dibromobenzene).

Hence, Statement I is correct, but Statement II is incorrect.

Pattern Recognition

Dipole tracking rule: Para-substituted benzenes with identical groups possess a structural center of inversion, guaranteeing a net dipole moment of exactly zero (μ = 0). They can never be more polar than any asymmetric ortho or meta structural isomer.

Chapter Mix

Class 12 Chemistry: Haloalkanes and Haloarenes

Q43 jee_main_2025_24_jan_evening Nucleophilic Substitution Reactions
The structure of the major product formed in the following reaction is :
Nucleophilic Substitution Reactions diagram for Q43 - JEE Main 2025 Evening
The reaction shows a dihalogenated aromatic derivative reacting with silver cyanide to generate a major product.
  • A. \text{Structure Option (1)}
  • B. \text{Structure Option (2)}
  • C. \text{Structure Option (3)}
  • D. \text{Structure Option (4)}

Solution

Core Logic

The substrate contains two distinct carbon-halogen bonds: an aryl-bromide bond (Ar-Br) on the ring and an aliphatic alkyl-chloride bond (CH₂-Cl) on the side chain.

  • Aryl Halide Site (Csp²-Br): The bromine atom attached directly to the aromatic ring does not undergo standard nucleophilic substitution (SN2 or SN1) under normal conditions due to resonance stabilization, which gives the bond partial double-bond character.
  • Alkyl Halide Site (Csp³-Cl): The side-chain aliphatic carbon bond undergoes smooth, unhindered nucleophilic substitution.
  • When reacting with silver cyanide (AgCN): AgCN is predominantly covalent. The lone pair on the nitrogen atom acts as the primary nucleophilic center rather than the carbon atom. Consequently, substitution at the aliphatic site yields an isonitrile (-NC) derivative as the major product, leaving the aryl bromide group completely untouched.

Step 1: Structural Resolution

The reaction progresses cleanly at the side-chain carbon:

Nucleophilic Substitution Reactions solution diagram for Q43 - JEE Main 2025 Evening
The reaction shows a dihalogenated aromatic derivative reacting with silver cyanide to generate a major product.

Pattern Recognition

Remember the key selectivity rule for cyanide nucleophiles:

  • KCN / NaCN arrow ionic reagents arrow attacks via carbon to form a Nitrile (-CN).
  • AgCN arrow covalent reagent arrow attacks via nitrogen to form an Isonitrile (-NC).
Chapter Mix

Class 12 Chemistry: Haloalkanes and Haloarenes

Q44 jee_main_2025_24_jan_morning Nucleophilic Substitution Reactions
Given below are two statements : Statement-I: The conversion proceeds well in the less polar medium. CH₃-CH₂-CH₂-CH₂-Cl HO^- CH₃-CH₂-CH₂-CH₂-OH + Cl^- Statement-II: The conversion proceeds well in the more polar medium. CH₃-CH₂-CH₂-CH₂-Cl R₃N [CH₃-CH₂-CH₂-CH₂-NR₃]⁺Cl^-
  • A. Both statement I and statement II are true
  • B. Both statement I and statement II are false.
  • C. Statement I is false but statement II is true
  • D. Statement I is true but statement II is false

Solution

Core Logic

Analyzing the solvent effects on reaction kinetics:

  • In Statement-I, the reaction involves an anionic nucleophile (OH⁻), creating a highly localized charge density on the reactant side. The resulting transition state disperses this negative charge over a larger volume, lowering its charge density. Highly polar solvents strongly solvate the reactant ion, increasing the activation energy barrier. Consequently, less polar solvents accelerate this process.
    SN2 pathway charge density solvent dynamics part 1
    SN2 pathway charge density solvent dynamics part 1
  • In Statement-II, the reaction begins with neutral precursors (R₃N and alkyl chloride). The resulting transition state develops partial charges (δ+ and δ-) as the new bond forms, increasing its charge density relative to the reactants. Polar solvents stabilize this charged transition state, lowering the activation energy barrier. Thus, highly polar media accelerate this substitution pathway.
    SN2 pathway charge density solvent dynamics part 1
    SN2 pathway charge density solvent dynamics part 1
Pattern Recognition

If the transition state concentrates charge relative to the reactants, polar solvents accelerate the reaction. If the transition state disperses charge, less polar solvents are favored.

Chapter Mix

Class 12 Chemistry: Haloalkanes and Haloarenes

Q jee_main_2025_28_jan_evening Elimination Reactions (E2)
The major product of the following reaction is:
Dihaloalkane starting reactant structure for Q38
The image details a multi-halogenated hydrocarbon chain reacting with excess ethanolic potassium hydroxide under heating conditions.
  • A. 6-Phenylhepta-2,4-diene
  • B. 2-Phenylhepta-2,5-diene
  • C. 6-Phenylhepta-3,5-diene
  • D. 2-Phenylhepta-2,4-diene

Solution

Related Formula

Base-induced dehydrohalogenation follows the Zaitsev rule to maximize thermodynamic stability via conjugated double bond networks:

R-CHX-CH₂-CHX-R' excess KOH/EtOH, Δ Conjugated Diene
Core Logic

The reactant is a dihalide containing a phenyl substitution. Treating with excess alcoholic KOH and heat induces double dehydrohalogenation via successive E2 elimination pathways.

The eliminations occur to yield the most stable, highly conjugated product where the double bonds are conjugated with each other and, if possible, with the aromatic phenyl ring system.

Step 1: Eliminating and Tracking Conjugation

Eliminating the first and second equivalents of HBr sets up a conjugated diene system along the heptadiene chain.

Tracing carbon numbers correctly from the end closest to the phenyl ring reveals that the conjugated diene centers sit across carbons 2 and 4, producing 2-Phenylhepta-2,4-diene.

Elimination mechanism steps for conjugated diene synthesis
The image details a multi-halogenated hydrocarbon chain reacting with excess ethanolic potassium hydroxide under heating conditions.

Pattern Recognition

When dealing with excess elimination agents on dihalides, look for options that form a continuous conjugated diene structure (alternating double-single-double bonds). This conjugation offers significant thermodynamic stability, especially when directly extended from a phenyl group.

Chapter Mix

Class 12 Chemistry: Haloalkanes and Haloarenes

More Haloalkanes and Haloarenes Questions — jee_main_2025_28_jan_morning

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