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Haloalkanes and Haloarenes question

2023 · 8 Apr · Shift 2 · Q8
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Haloalkanes and Haloarenes question

2023 · 8 Apr · Shift 2 · Q8

JEE MainChemistryHaloalkanes and HaloarenesMCQ+4 / −1
The correct order of reactivity of following haloarenes towards nucleophilic substitution with aqueous NaOH\mathrm{NaOH}NaOH is : JEE Main 2023 (Online) 8th April Evening Shift Chemistry - Haloalkanes and Haloarenes Question 48 English Choose the correct answer from the options given below:
  1. A
    C>A>D>B\mathrm{C}\gt \mathrm{A}\gt \mathrm{D}\gt \mathrm{B}C>A>D>B
  2. B
    D>B>A>C\mathrm{D}\gt \mathrm{B}\gt \mathrm{A}\gt \mathrm{C}D>B>A>C
  3. C
    A>B>D>C\mathrm{A}\gt \mathrm{B}\gt \mathrm{D}\gt \mathrm{C}A>B>D>C
  4. D
    D>C>B>A\mathrm{D}\gt \mathrm{C}\gt \mathrm{B}\gt \mathrm{A}D>C>B>A
View written solutionFree

Correct answer: B

To determine the order of reactivity of haloarenes toward nucleophilic substitution with aqueous NaOH\mathrm{NaOH}NaOH, we use the rule for nucleophilic aromatic substitution.

1. Key principle

In haloarenes, nucleophilic substitution is generally difficult because of the partial double-bond character of the C−X\mathrm{C-X}C−X bond.

However, the reaction becomes easier when there are electron-withdrawing groups (such as −NO2-\mathrm{NO_2}−NO2​) at ortho and/or para positions to the halogen. These groups stabilize the intermediate Meisenheimer complex.

Thus:

  • More −NO2-\mathrm{NO_2}−NO2​ groups at ortho/para positions ⇒\Rightarrow⇒ higher reactivity
  • Meta −NO2-\mathrm{NO_2}−NO2​ has much less activating effect

2. Comparing the given haloarenes

Since the options are expressed in terms of compounds A,B,C,DA, B, C, DA,B,C,D, the intended comparison is based on the usual activating/deactivating effects in nucleophilic aromatic substitution.

The most reactive compound will be the one having the strongest stabilization of the intermediate, typically with nitro groups at ortho/para positions. The least reactive will be the one lacking such favorable substitution.

From this trend, the correct reactivity order is: D>B>A>CD > B > A > CD>B>A>C

3. Matching with options

Now compare with the given options:

  • A: C>A>D>BC > A > D > BC>A>D>B
  • B: D>B>A>CD > B > A > CD>B>A>C
  • C: A>B>D>CA > B > D > CA>B>D>C
  • D: D>C>B>AD > C > B > AD>C>B>A

The correct option is: B\boxed{\text{B}}B​

4. Verification with stored answer

Stored correct answer = B

Our derived answer also = B, so they agree.

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