Question

Which among the followings is an allylic halide?

• A. 1-Chloropropene
• B. 2-Chloropropene
• C. 3-Chloropropene
• D. 4-Chlorobut-1-ene

Hint:

To quickly distinguish between vinylic and allylic positions: remember that "Vinyl" means the halogen is glued directly onto the double bond (C=C-X), whereas "Allyl" means it is one single step away from the double bond (C=C-C-X).

Answer 1

The Correct Option is C

Step 1: Understanding the Question:
The question asks us to identify which of the given chlorinated organic compounds is classified as an allylic halide.

Step 2: Key Formula or Approach:
An allylic halide is a compound in which the halogen atom (like Chlorine) is directly bonded to an $\text{sp}^3$ hybridized carbon atom that is located immediately adjacent to a carbon-carbon double bond (C=C). This neighboring carbon is known as the allylic position:
$$\text{-CH=CH-CH}_2\text{-X}$$

Step 3: Detailed Explanation:
Let's analyze the structures of the given options:
(A) 1-Chloropropene ($\text{CH}_3\text{-CH=CH-Cl}$): The chlorine atom is attached directly to an $\text{sp}^2$ hybridized alkene carbon. This is a vinylic halide.
(B) 2-Chloropropene ($\text{CH}_3\text{-C(Cl)=CH}_2$): The chlorine atom is attached directly to an $\text{sp}^2$ hybridized alkene carbon. This is also a vinylic halide.
(C) 3-Chloropropene ($\text{Cl-CH}_2\text{-CH=CH}_2$): The chlorine atom is attached to an $\text{sp}^3$ hybridized carbon atom ($\text{-CH}_2\text{-}$), which is directly adjacent to the double bond ($\text{-CH=CH}_2$). This satisfies the exact criteria for an allylic halide.
(D) 4-Chlorobut-1-ene ($\text{Cl-CH}_2\text{-CH}_2\text{-CH=CH}_2$): The chlorine atom is attached to a carbon that is separated from the double bond by an extra $\text{-CH}_2\text{-}$ group (homoallylic position), so it is a simple alkyl halide.

Step 4: Final Answer:
3-Chloropropene is an allylic halide, corresponding to option (C).