Which one is not an allylic halide?

Options

A. 3 - chloro cyclo hex -1 - ene
B. 1 - chloro but -2- ene
C. 1 - chloro prop -1- ene.
D. 3 - chloro prop -1- ene

Answer

To determine which compound is not an allylic halide, we first need to understand the definition of an allylic halide. An allylic halide is a compound where a halogen atom (like Cl) is attached to a carbon atom that is sp³ hybridized and is adjacent (alpha position) to a carbon-carbon double bond.

### Step-by-Step Solution:

1. **Identify the Structure of Each Compound**:
- For each compound given, we need to draw the structure and identify the position of the halogen and the double bond.

2. **Check for Allylic Halide Criteria**:
- The carbon atom to which the halogen is attached must be sp³ hybridized.
- The carbon atom with the halogen must be adjacent to a carbon-carbon double bond.

3. **Analyze Each Compound**:
- **3-chloro-cyclo-hex-1-ene**:
- Structure: The chlorine is on the 3rd carbon of cyclohexene (which has a double bond between C1 and C2). The carbon with Cl is sp³ and adjacent to the double bond. This is an allylic halide.

- **1-chloro-2-butene**:
- Structure: The chlorine is on the 1st carbon of 2-butene (double bond between C2 and C3). The carbon with Cl is sp³ and adjacent to the double bond. This is also an allylic halide.

- **1-chloroprop-1-ene**:
- Structure: The chlorine is on the 1st carbon of prop-1-ene (double bond between C1 and C2). The carbon with Cl is sp² (not sp³) and directly involved in the double bond. This is NOT an allylic halide.

- **3-chloro-1-pentene**:
- Structure: The chlorine is on the 3rd carbon of 1-pentene (double bond between C1 and C2). The carbon with Cl is sp³ and adjacent to the double bond. This is an allylic halide.

4. **Conclusion**:
- The compound that is not an allylic halide is **1-chloroprop-1-ene**.

### Final Answer:
**1-chloroprop-1-ene is not an allylic halide.**

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