Alkenes
Markovnikov's rule predicts that the addition of HBr to propene (CH₃–CH=CH₂) will predominantly yield:
Select the correct option:
Solution
2-Bromopropane
Markovnikov's rule states that in electrophilic addition of a protic acid HX to an unsymmetrical alkene, the proton (H⁺) adds to the carbon bearing more hydrogens (forming the more stable carbocation), while X⁻ adds to the carbon bearing fewer hydrogens. In propene, C1 (=CH₂) bears 2 H atoms and C2 (CH=) bears 1 H atom. Protonation of C1 generates a secondary carbocation at C2 (CH₃–CH⁺–CH₃), which is more stable than the primary carbocation at C1. Br⁻ then attacks C2, giving 2-bromopropane (CH₃CHBrCH₃) as the major product. 1-Bromopropane would form from the less stable primary carbocation and is the minor product.
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About This Question
- Subject
- chemistry
- Chapter
- hydrocarbons
- Topic
- alkenes
- Difficulty
- Easy
- Year
- 2025
Solution
Correct Answer:
2-Bromopropane
Markovnikov's rule states that in electrophilic addition of a protic acid HX to an unsymmetrical alkene, the proton (H⁺) adds to the carbon bearing more hydrogens (forming the more stable carbocation), while X⁻ adds to the carbon bearing fewer hydrogens. In propene, C1 (=CH₂) bears 2 H atoms and C2 (CH=) bears 1 H atom. Protonation of C1 generates a secondary carbocation at C2 (CH₃–CH⁺–CH₃), which is more stable than the primary carbocation at C1. Br⁻ then attacks C2, giving 2-bromopropane (CH₃CHBrCH₃) as the major product. 1-Bromopropane would form from the less stable primary carbocation and is the minor product.
This easy difficulty chemistry question is from the chapter hydrocarbons, covering the topic of alkenes. It appeared in the 2025 exam.
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