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Hydrocarbons question

2019 · 9 Apr · Shift 2 · Q5
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Hydrocarbons question

2019 · 9 Apr · Shift 2 · Q5

JEE MainChemistryHydrocarbonsMCQ+4 / −1
Which of the following potential energy (PE) diagrams represents the SN1 reaction?
  1. A
    JEE Main 2019 (Online) 9th April Evening Slot Chemistry - Hydrocarbons Question 112 English Option 1
  2. B
    JEE Main 2019 (Online) 9th April Evening Slot Chemistry - Hydrocarbons Question 112 English Option 2
  3. C
    JEE Main 2019 (Online) 9th April Evening Slot Chemistry - Hydrocarbons Question 112 English Option 3
  4. D
    JEE Main 2019 (Online) 9th April Evening Slot Chemistry - Hydrocarbons Question 112 English Option 4
View written solutionFree

Correct answer: A

  1. In an SN1\mathrm{S_N1}SN​1 reaction, the mechanism occurs in two steps:

    • Step 1: Formation of a carbocation intermediate by leaving group departure.
    • Step 2: Nucleophile attacks the carbocation.

  2. Since there are two elementary steps, the potential energy diagram must show:

    • Two transition states ⇒\Rightarrow⇒ two peaks
    • One intermediate ⇒\Rightarrow⇒ one valley between the peaks

  3. Also, in most SN1\mathrm{S_N1}SN​1 reactions, the first step is slow (rate-determining step), because bond breaking to form the carbocation requires significant energy.

    • Therefore, the first peak is usually higher than the second peak.

  4. So the correct PE diagram for an SN1\mathrm{S_N1}SN​1 reaction should have:

    • two maxima
    • one intermediate between them
    • first activation barrier larger than the second

  5. Among the given options, the diagram matching this description is Option A.

Therefore, the SN1\mathrm{S_N1}SN​1 potential energy diagram is represented by A.

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