Structure and Reactivity of Alkenes

Structure and Reactivity of Alkenes MDCAT MCQs with answers

9 past paper MCQs on Structure and Reactivity of Alkenes, from the Chemistry of Hydrocarbons unit of MDCAT Chemistry. The year each question appeared is shown where known; tap “Show answer” for the correct option and a short solution.

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1.The addition reaction of 2-butene with HBr produces: (MDCAT 2023)

  1. 1-bromobutane
  2. 2-bromobutane
  3. 3-bromobutane
  4. 2,3-dibromobutane
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Correct answer: (b) 2-bromobutane

Either carbon of the double bond is equivalent here, so the bromine ends up on carbon 2.

2.The addition of water to propene in the presence of sulfuric acid produces: (KMU MDCAT 2025)

  1. Propane
  2. Propan-2-ol
  3. Butanol
  4. Ethanol
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Correct answer: (b) Propan-2-ol

The proton adds to give the more stable secondary carbocation, so the hydroxyl ends on the middle carbon.

3.Addition of HBr to isobutylene mainly gives (KMU MDCAT 2024)

  1. isobutyl bromide
  2. n-butyl bromide
  3. sec-butyl bromide
  4. tert-butyl bromide
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Correct answer: (d) tert-butyl bromide

By Markovnikov’s rule the bromine goes to the more substituted carbon, giving the tertiary halide.

4.Identify the alkene which gives only one type of aldehyde upon ozonolysis: (NUMS MDCAT 2024)

  1. 1-pentene
  2. 2-methyl propene
  3. 2-butene
  4. 2,3-dimethyl-2-butene
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Correct answer: (c) 2-butene

But-2-ene is symmetrical, so both halves give the same aldehyde, acetaldehyde.

5.Major product of the following reaction is: CH2=CH-CH2-CH3 + HBr -> (PMC MDCAT 2022)

  1. CH2 (Br)-CH2 -CH2 -CH3
  2. CH3-CH(Br)-CH2-CH3
  3. CH2=CH-CH(Br)-CH3
  4. CH2=CH-CH2-CH2(Br)
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Correct answer: (b) CH3-CH(Br)-CH2-CH3

By Markovnikov’s rule the bromine adds to the carbon already carrying more substituents.

6.Which of the following method is used to prepare Ethylene glycol from ethene? (PMC Practice 2021)

  1. Dehydration
  2. Hydroxylation
  3. Hydration
  4. Luca's test
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Correct answer: (b) Hydroxylation

Cold alkaline permanganate adds two hydroxyl groups across the double bond.

7.Alkenes undergo: (UHS MDCAT 2019)

  1. Electrophilic Addition
  2. Electrophilic substitution
  3. Nucleophilic substitution
  4. Nucleophilic addition
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Correct answer: (a) Electrophilic Addition

The pi electrons of the double bond attract an electrophile, which then adds across it.

8.Bromination of alkene is shown in the following reaction. This reaction is used for: (UHS MDCAT 2018)

  1. Detection of ketones
  2. Detection of double bond
  3. Identification of Primary and Secondary alcohols
  4. Detection of Aldehydes
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Correct answer: (b) Detection of double bond

Bromine water is decolourized by an alkene, which is the test for a double bond.

9.What do you call the process when sodium periodate is reacted to 1,2-diols? (UHS MDCAT 2017)

  1. Protonation
  2. Epoxidification
  3. Oxidative cleavage
  4. Esterification
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Correct answer: (c) Oxidative cleavage

Periodate splits the bond between the two hydroxyl-bearing carbons, which is oxidative cleavage.

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