Unit 16: Organic Compounds Containing Halogens — Online MCQ Test
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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 ofsubstitution 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: Statement I: CH3-O-CH2-Cl will undergo SN1 reaction though it is a primary halide. Statement II: CH3-O-CH2-Cl will not undergo SN2 reaction very easily though it is a primary halide. In the light of the above statements, choose the most appropriate answer from the options given below:
- A. Both Statement I and Statement II are incorrect
- B. Both Statement I and Statement II are correct
- C. Statement I is incorrect but Statement II is correct
- D. Statement I is correct but Statement II is incorrect
Answer: B. Both Statement I and Statement II are correct
CH3-O-CH2-Cl is highly reactive in SN1 due to resonance stabilization of the intermediate oxonium carbocation, and steric/electronic effects influence SN2 kinetics.
CH3-O-CH2-Cl is highly reactive in SN1 due to resonance stabilization of the intermediate oxonium carbocation, and steric/electronic effects influence SN2 kinetics.
The correct order of the rate of the reaction (substitution) with respect to nucleophiles for CH3Br is:
- A. (1) PhO- > OH- > CH3COO- > ClO4-
- B. (2) ClO4- > CH3COO- > OH- > PhO-
- C. (3) CH3COO- > PhO- > OH- > ClO4-
- D. (4) OH- > PhO- > CH3COO- > ClO4-
Answer: D. (4) OH- > PhO- > CH3COO- > ClO4-
Nucleophilicity is inversely proportional to the stability of the anion. Stronger bases (conjugate bases of weaker acids) are better nucleophiles. OH- is the strongest base among the options, followed by phenoxide, acetate, and perchlorate.
Nucleophilicity is inversely proportional to the stability of the anion. Stronger bases (conjugate bases of weaker acids) are better nucleophiles. OH- is the strongest base among the options, followed by phenoxide, acetate, and perchlorate.
The correct order of reactivity of CH3Br in methanol with the following nucleophiles is F–, I–, C2H5O– and C6H5O–.
- A. C6H5O– > C2H5O– > I– > F–
- B. I– > C2H5O– > C6H5O– > F–
- C. I– > C2H5O– > F– > C6H5O–
- D. C6H5O– > F– > C2H5O– > I–
Answer: B. I– > C2H5O– > C6H5O– > F–
Reactivity follows nucleophilicity order: C2H5O– (strong base/nucleophile) > C6H5O– (less basic due to resonance) > I–. F– is a poor nucleophile in protic solvents like methanol due to strong solvation.
Reactivity follows nucleophilicity order: C2H5O– (strong base/nucleophile) > C6H5O– (less basic due to resonance) > I–. F– is a poor nucleophile in protic solvents like methanol due to strong solvation.
The correct order of the rate of reaction of the following reactants with nucleophile by SN1 mechanism is : (Given : Structure I and II are rigid)
- A. IV < III < II < I
- B. III < I < II < IV
- C. II < I < III < IV
- D. I < II < III < IV
Answer: C. II < I < III < IV
The rate of SN1 reaction depends on the stability of the carbocation formed. Structures I and II are bridgehead carbons and are highly unstable due to Bredt's rule. I has more +I effect than II. Therefore the order is II < I < III < IV.
The rate of SN1 reaction depends on the stability of the carbocation formed. Structures I and II are bridgehead carbons and are highly unstable due to Bredt's rule. I has more +I effect than II. Therefore the order is II < I < III < IV.
Identify the correct order of reactivity for the following pairs towards the respective mechanism
- A. $(B), (C) and (D) only$
- B. $(A), (B) and (D) only$
- C. $(A), (C) and (D) only$
- D. $(A), (B), (C) and (D)$
Answer: D. $(A), (B), (C) and (D)$
Check each statement: (A) For $S_N2$, the less hindered primary bromide reacts faster than the tertiary bromide, so the given order is correct. (B) For $S_N1$, the benzylic bromide forms a resonance-stabilized carbocation and is more reactive than the non-benzylic alkyl bromide, so the given order is correct. (C) In electrophilic substitution, chlorobenzene is more reactive than nitrochlorobenzene because $NO_2$ is strongly deactivating, so the given order is correct. (D) In nucleophilic substitution on aryl bromides, nitro-substituted bromobenzene is more reactive than bromobenzene because $NO_2$ activates the ring toward nucleophilic attack, so the given order is correct. Hence all four statements are correct.
Check each statement: (A) For $S_N2$, the less hindered primary bromide reacts faster than the tertiary bromide, so the given order is correct. (B) For $S_N1$, the benzylic bromide forms a resonance-stabilized carbocation and is more reactive than the non-benzylic alkyl bromide, so the given order is correct. (C) In electrophilic substitution, chlorobenzene is more reactive than nitrochlorobenzene because $NO_2$ is strongly deactivating, so the given order is correct. (D) In nucleophilic substitution on aryl bromides, nitro-substituted bromobenzene is more reactive than bromobenzene because $NO_2$ activates the ring toward nucleophilic attack, so the given order is correct. Hence all four statements are correct.