Unit 16: Organic Compounds Containing Halogens — Online MCQ Test
CHEMISTRY · NEET (All) · NEET
Practice Unit 16: Organic Compounds Containing Halogens with a free chapter-wise online MCQ test.
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....
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Unit 16: Organic Compounds Containing Halogens — Important Questions & Answers
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.
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.
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.
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.
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.
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.
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.
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.
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.
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).
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).