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Haloalkanes and Haloarenes
Elimination Reactions
3 questions from 3 papers, each with its answer.
- questions
- 3
- papers
- 3
- years asked, 2017–2026
- 2 of 10
- of Haloalkanes and Haloarenes
- 5.45%
Appears in
Concepts tested
- C-X bond strength and reactivity
- dehydrohalogenation and Zaitsev's rule
- Saytzeff rule
All Questions
2021 1 question
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The major product formed in dehydrohalogenation reaction of 2-Bromo pentane is Pent-2-ene. This product formation is based on?$CH_3-CH_2-CH_2-CH(Br)-CH_3 \xrightarrow{dehydrohalogenation} CH_3-CH_2-CH=CH-CH_3$ (major) The more substituted alkene (pent-2-ene) is formed as the major product according to Saytzeff's rule.
2020 1 question
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Elimination reaction of 2-Bromo-pentane to form pent-2-ene is: (a) $\beta$-Elimination reaction (b) Follows Zaitsev rule (c) Dehydrohalogenation reaction (d) Dehydration reaction$CH_3-CH(Br)-CH_2-CH_2-CH_3 \xrightarrow{base} CH_3-CH=CH-CH_2-CH_3$ A $\beta$-hydrogen is abstracted, so it is a $\beta$-elimination reaction. The more substituted alkene (pent-2-ene) is formed, so it follows Zaitsev's rule. H and Br are removed, so it is a dehydrohalogenation reaction (not dehydration). So (a), (b) and (c) are correct.
2002 AIPMT 1 question
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Reactivity order of halides for dehydrohalogenation is : -In dehydrohalogenation (elimination with alcoholic KOH), the C–X bond is broken.
The C–X bond strength decreases in the order C–F $\gt$ C–Cl $\gt$ C–Br $\gt$ C–I, because the halogen atom becomes larger and the overlap weaker.
The weaker the bond, the easier it breaks; also $I^-$ is the best leaving group.
So the reactivity order is R–I $\gt$ R–Br $\gt$ R–Cl $\gt$ R–F.