Question

Which among the following is an allylic halide?

• A. 1-Bromopropene
• B. 2-Bromopropene
• C. 3-Bromopropene
• D. 4-Bromobut-1-ene

Hint:

Allylic: $X$ on $sp^3$ C next to $C=C$. Vinylic: $X$ directly on $sp^2$ C of $C=C$.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
An allylic halide is a compound where the halogen atom is bonded to an $sp^3$ hybridized carbon atom that is adjacent to a carbon-carbon double bond ($\text{C}=\text{C}$).
Step 2: Key Formula or Approach:
Identify the structure where $\text{X}$ (halogen) is on a carbon next to the double bond: $\text{C}=\text{C}-\text{C}-\text{X}$.
Step 3: Detailed Explanation:
(A) 1-Bromopropene: $\text{CH}_3-\text{CH}=\text{CH}-\text{Br}$. Halogen is on the vinylic carbon.
(B) 2-Bromopropene: $\text{CH}_3-\text{C}(\text{Br})=\text{CH}_2$. Halogen is on the vinylic carbon.
(C) 3-Bromopropene: $\text{CH}_2=\text{CH}-\text{CH}_2-\text{Br}$. Here, the Br is attached to an $sp^3$ carbon adjacent to the double bond. This is an allylic halide.
(D) 4-Bromobut-1-ene: $\text{CH}_2=\text{CH}-\text{CH}_2-\text{CH}_2-\text{Br}$. The halogen is two carbons away from the double bond.
Step 4: Final Answer:
3-Bromopropene is the allylic halide.