Question

The decreasing order of reactivity towards dehydrohalogenation (\(E_1\)) reaction of the following compounds is: 

 

• A. \( D>B>C>A \)
• B. \( B>D>A>C \)
• C. \( B>D>C>A \)
• D. \( B>A>D>C \)

Hint:

In \(E_1\) reactions, the rate-determining step is the formation of the carbocation. The more stable the carbocation, the faster the reaction.

Answer 1

The Correct Option is A

Step 1: Understanding the \(E_1\) Mechanism
The \(E_1\) (unimolecular elimination) reaction involves the formation of a carbocation intermediate.
The stability of the carbocation determines the reactivity: the more stable the carbocation, the faster the reaction.
Step 2: Analyzing the Given Compounds
The compounds contain halides (\(\text{Cl}\)) attached to different carbon atoms.
The reactivity order depends on the stability of the carbocation formed after the loss of \(\text{Cl}^-\).
Step 3: Determining the Order of Reactivity
(A) Primary Carbocation: Least stable, leading to the slowest reaction.
(B) Carbocation Undergoing Rearrangement: Results in a more stable secondary or tertiary carbocation, enhancing reactivity.
(C) Five Hyperconjugating Structures: Provides moderate stability.
(D) Resonance-Stabilized Carbocation: Most stable due to delocalization, increasing reactivity.
Step 4: Final Order of Reactivity
The stability of carbocations follows: \[ D>B>C>A \] Final Answer: The correct order is \( D>B>C>A \).