Chapter Exam

Unit 16: Organic Compounds Containing Halogens — Online MCQ Test

Q: Given below are two statements: Statement I: Aniline does not undergo Friedel-Crafts alkylation reaction. Statement II: Aniline cannot be prepared through Gabriel synthesis. In the light of the above statements, choose the correct answer from the options given below:

Answer: C. Both Statement I and Statement II are correct. — Aniline does not undergo Friedel-Crafts alkylation because the amino group forms a complex with Lewis acid catalysts such as AlCl3. Gabriel synthesis is used for preparing primary aliphatic amines, not aniline, so aniline cannot be prepared by Gabriel synthesis.

Q: The products A and B obtained in the following reactions, respectively, are: 3ROH + PCl3 → 3RCl + A ROH + PCl5 → RCl + HCl + B

Answer: B. H3PO3 and POCl3 — Alcohol with PCl3 gives phosphorous acid H3PO3. With PCl5, the by-product is phosphoryl chloride POCl3.

Q: Identify A and predict the type of reaction: OCH3-substituted bromobenzene reacts with NaNH2 to give A.

Answer: C. Methoxyaniline; substitution reaction — NaNH2 converts aryl halide to aniline derivative via the benzyne mechanism. The product is methoxyaniline, and the reaction is an elimination-addition substitution, not cine substitution.

Q: The reaction R-ONa + Me-I -> R-O-Me + NaI can be classified as :-

Answer: A. Williamson ether synthesis reaction — Williamson ether synthesis involves the nucleophilic substitution of an alkyl halide by an alkoxide ion to form an ether.

Q: Consider the reaction CH3CH2CH2Br + NaCN → CH3CH2CH2CN + NaBr. This reaction will be the fastest in :

Answer: A. N, N’-dimethylformamide (DMF) — This reaction proceeds via an SN2 mechanism, which is significantly accelerated in polar aprotic solvents like DMF because they do not solvate the nucleophile (CN-) as strongly as protic solvents.

Q: The compound C7H8 undergoes a series of reactions (Chlorination/Fe, Zn/HCl). The product 'C' is

Answer: A. m-bromotoluene — The reaction sequence on toluene leads to side-chain chlorination followed by bromination and final reduction, directing the bromine to the meta position due to the trichloromethyl group.

Q: In the reaction shown, the electrophile involved is

Answer: A. dichlorocarbene (:CCl2) — The reaction likely involves generation of dichlorocarbene (:CCl2), the reactive electrophile in such transformations.

Q: Identify compound X in the following sequence of reactions: Toluene → (Cl₂/hν) → X → (H₂O, 373 K) → CHO (benzaldehyde)

Answer: A. C₆H₅CHCl₂ (benzal chloride) — Toluene reacts with Cl₂ under UV light (hν) to give benzal chloride (C₆H₅CHCl₂, i.e., dichloromethyl benzene) as X. Benzal chloride on hydrolysis with water at 373 K gives benzaldehyde (CHO).

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Practice Unit 16: Organic Compounds Containing Halogens with a free chapter-wise online MCQ test for NEET NEET (All) CHEMISTRY. This chapter covers: General methods of preparation properties and reactions; Nature of C-X bond; Mechanisms of substitution reactions. Uses; Environmental effects of chloroform iodoform freons and DDT.... AI-generated questions from basic to board-exam level, with instant results and explanations.

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Unit 16: Organic Compounds Containing Halogens — Important Questions & Answers (FAQ)

Frequently asked questions from NEET NEET (All) CHEMISTRY — Unit 16: Organic Compounds Containing Halogens, with answers and explanations. These are sample questions; the exam has its own separate question set.

Given below are two statements: Assertion (A): R-I undergoes SN2 reaction faster than R-Cl. Reason (R): Iodine is a better leaving group because of its large size.

A. Both A and R are true and R is the correct explanation of A. ✓
B. Both A and R are true but R is not the correct explanation of A.
C. A is true but R is false.
D. A is false but R is true.

Answer: A. Both A and R are true and R is the correct explanation of A.
Larger halides (I-) have weaker C-X bonds and are more stable anions, making them better leaving groups for SN2.

Given below are two statements: one is labelled as Assertion (A) and the other is labelled as Reason (R): Assertion (A): RI undergoes SN2 reaction faster than RCl. Reason (R): Iodine is a better leaving group because of its large size. In the light of the above statements, choose the correct answer from the options given below:

A. Both A and R are true and R is the correct explanation of A. ✓
B. Both A and R are true but R is not the correct explanation of A.
C. A is true but R is false.
D. A is false but R is true.

Answer: A. Both A and R are true and R is the correct explanation of A.
Iodide is a weaker base than chloride, making it a better leaving group. Higher reactivity in SN2 is directly proportional to the leaving group ability.

Given below are two statements: Statement I: Aniline does not undergo Friedel-Crafts alkylation reaction. Statement II: Aniline cannot be prepared through Gabriel synthesis. In the light of the above statements, choose the correct answer from the options given below:

A. Statement I is correct but Statement II is false.
B. Statement I is incorrect but Statement II is correct.
C. Both Statement I and Statement II are correct. ✓
D. Both Statement I and Statement II are incorrect.

Answer: C. Both Statement I and Statement II are correct.
Aniline does not undergo Friedel-Crafts alkylation because the amino group forms a complex with Lewis acid catalysts such as AlCl3. Gabriel synthesis is used for preparing primary aliphatic amines, not aniline, so aniline cannot be prepared by Gabriel synthesis.

The products A and B obtained in the following reactions, respectively, are: 3ROH + PCl3 → 3RCl + A ROH + PCl5 → RCl + HCl + B

A. H3PO4 and POCl3
B. H3PO3 and POCl3 ✓
C. POCl3 and H3PO3
D. POCl3 and H3PO4

Answer: B. H3PO3 and POCl3
Alcohol with PCl3 gives phosphorous acid H3PO3. With PCl5, the by-product is phosphoryl chloride POCl3.

Identify A and predict the type of reaction: OCH3-substituted bromobenzene reacts with NaNH2 to give A.

A. Unchanged bromomethoxybenzene; cine substitution reaction
B. Methoxybenzene; cine substitution reaction
C. Methoxyaniline; substitution reaction ✓
D. Methoxyaniline; elimination-addition reaction

Answer: C. Methoxyaniline; substitution reaction
NaNH2 converts aryl halide to aniline derivative via the benzyne mechanism. The product is methoxyaniline, and the reaction is an elimination-addition substitution, not cine substitution.

The reaction R-ONa + Me-I -> R-O-Me + NaI can be classified as :-

A. Williamson ether synthesis reaction ✓
B. Alcohol formation reaction
C. Dehydration reaction
D. Williamson alcohol synthesis reaction

Answer: A. Williamson ether synthesis reaction
Williamson ether synthesis involves the nucleophilic substitution of an alkyl halide by an alkoxide ion to form an ether.

Consider the reaction CH3CH2CH2Br + NaCN → CH3CH2CH2CN + NaBr. This reaction will be the fastest in :

A. N, N’-dimethylformamide (DMF) ✓
B. Water
C. Ethanol
D. Methanol

Answer: A. N, N’-dimethylformamide (DMF)
This reaction proceeds via an SN2 mechanism, which is significantly accelerated in polar aprotic solvents like DMF because they do not solvate the nucleophile (CN-) as strongly as protic solvents.

The compound C7H8 undergoes a series of reactions (Chlorination/Fe, Zn/HCl). The product 'C' is

A. m-bromotoluene ✓
B. p-bromotoluene
C. 3-bromo-2,4,6-trichlorotoluene
D. o-bromotoluene

Answer: A. m-bromotoluene
The reaction sequence on toluene leads to side-chain chlorination followed by bromination and final reduction, directing the bromine to the meta position due to the trichloromethyl group.

In the reaction shown, the electrophile involved is

A. dichlorocarbene (:CCl2) ✓
B. dichloromethyl anion (CHCl2−)
C. formyl cation (CHO+)
D. dichloromethyl cation (CHCl2+)

Answer: A. dichlorocarbene (:CCl2)
The reaction likely involves generation of dichlorocarbene (:CCl2), the reactive electrophile in such transformations.

Identify compound X in the following sequence of reactions: Toluene → (Cl₂/hν) → X → (H₂O, 373 K) → CHO (benzaldehyde)

A. C₆H₅CHCl₂ (benzal chloride) ✓
B. C₆H₅CCl₃ (benzotrichloride)
C. C₆H₄Cl–CH₃ (chlorotoluene)
D. C₆H₅CH₂Cl (benzyl chloride)

Answer: A. C₆H₅CHCl₂ (benzal chloride)
Toluene reacts with Cl₂ under UV light (hν) to give benzal chloride (C₆H₅CHCl₂, i.e., dichloromethyl benzene) as X. Benzal chloride on hydrolysis with water at 373 K gives benzaldehyde (CHO).

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