Question:
Which one of the following is not an allylic halide?
Which one of the following is not an allylic halide?
Show Hint
To identify an allylic halide, look for the pattern \(C=C-C-X\). If there is an extra carbon between the double bond and the carbon holding the halogen (\(C=C-C-C-X\)), it is no longer allylic.
Updated On: Apr 22, 2026
- 4-bromopent-2-ene
- 3-bromo-2-methylbut-1-ene
- 1-bromobut-2-ene
- 4-bromobut-1-ene
- 3-bromo-2-methylpropene
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The Correct Option is D
Solution and Explanation
Step 1: Understanding the Concept:
An allylic halide is a compound where the halogen atom (like Bromine) is bonded to an \(sp^3\) hybridized carbon atom which is directly adjacent to a carbon-carbon double bond (\(C=C\)). This specific position is called the "allylic position."
Step 2: Detailed Explanation:
1. 4-bromopent-2-ene: \(CH_3-CH=CH-CH(Br)-CH_3\). The Br is on a carbon adjacent to the double bond. (Allylic)
2. 3-bromo-2-methylbut-1-ene: \(CH_2=C(CH_3)-CH(Br)-CH_3\). The Br is on a carbon adjacent to the double bond. (Allylic)
3. 1-bromobut-2-ene: \(CH_3-CH=CH-CH_2Br\). The Br is on a carbon adjacent to the double bond. (Allylic)
4. 4-bromobut-1-ene: \(CH_2=CH-CH_2-CH_2Br\). The Br is attached to a carbon that is separated from the double bond by another carbon atom. (Not Allylic; this is a homoallylic position).
5. 3-bromo-2-methylpropene: \(CH_2=C(CH_3)-CH_2Br\). The Br is on a carbon adjacent to the double bond. (Allylic)
Step 3: Final Answer
4-bromobut-1-ene is not an allylic halide.
An allylic halide is a compound where the halogen atom (like Bromine) is bonded to an \(sp^3\) hybridized carbon atom which is directly adjacent to a carbon-carbon double bond (\(C=C\)). This specific position is called the "allylic position."
Step 2: Detailed Explanation:
1. 4-bromopent-2-ene: \(CH_3-CH=CH-CH(Br)-CH_3\). The Br is on a carbon adjacent to the double bond. (Allylic)
2. 3-bromo-2-methylbut-1-ene: \(CH_2=C(CH_3)-CH(Br)-CH_3\). The Br is on a carbon adjacent to the double bond. (Allylic)
3. 1-bromobut-2-ene: \(CH_3-CH=CH-CH_2Br\). The Br is on a carbon adjacent to the double bond. (Allylic)
4. 4-bromobut-1-ene: \(CH_2=CH-CH_2-CH_2Br\). The Br is attached to a carbon that is separated from the double bond by another carbon atom. (Not Allylic; this is a homoallylic position).
5. 3-bromo-2-methylpropene: \(CH_2=C(CH_3)-CH_2Br\). The Br is on a carbon adjacent to the double bond. (Allylic)
Step 3: Final Answer
4-bromobut-1-ene is not an allylic halide.
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