Reactions of Alkenes - Addition Reactions Markovnikovs Rule - UNSOLVED PRACTICE SET
Chapter: Hydrocarbons | Topic: Reactions of Alkenes Addition Reactions Markovnikovs Rule
REACTIONS OF ALKENES - ADDITION REACTIONS MARKOVNIKOVS RULE - UNSOLVED PRACTICE SET
Topic: Reactions of Alkenes Addition Reactions Markovnikovs Rule
Multiple Choice Questions
Q1. According to Markovnikov's rule, in the addition of HX to an unsymmetrical alkene:
- H attaches to the carbon with fewer hydrogen atoms
- H attaches to the carbon with more hydrogen atoms
- X attaches to the carbon with more hydrogen atoms
- The addition is random
Q2. The addition of HBr to propene in the presence of peroxide follows:
- Markovnikov's rule
- Anti-Markovnikov's rule
- No specific rule
- Zaitsev's rule
Q3. The product of hydration of propene in the presence of dilute H₂SO₄ is:
- Propan-1-ol
- Propan-2-ol
- Propanal
- Propanoic acid
Q4. The addition of Br₂ to ethene gives:
- 1,1-Dibromoethane
- 1,2-Dibromoethane
- Bromoethane
- No reaction
Q5. Hydroboration-oxidation of an alkene gives:
- Markovnikov alcohol
- Anti-Markovnikov alcohol
- Alkane
- Aldehyde
Q6. Ozonolysis of an alkene followed by reductive workup (Zn/H₂O) gives:
- Only ketones
- Only aldehydes
- Carbonyl compounds (aldehydes and/or ketones)
- Carboxylic acids
Short Answer Questions
Q7. State Markovnikov's rule. Explain why the addition of HCl to propene gives 2-chloropropane as the major product.
Q8. What is the peroxide effect (Kharasch effect)? Explain with the addition of HBr to propene in the presence of peroxide.
Q9. Write the products formed when 2-methylbut-2-ene reacts with:
(a) HBr
(b) Br₂/H₂O
(c) Cold dilute alkaline KMnO₄
Q10. Explain the mechanism of electrophilic addition of bromine to ethene. Why is this reaction used as a test for unsaturation?
Q11. Your school lab uses Baeyer's reagent (alkaline KMnO₄) to test for unsaturation. What colour change is observed, and what does it indicate? Write the reaction for ethene.
Q12. What is hydroboration-oxidation? Why does it give anti-Markovnikov addition of water to alkenes?
Long Answer Questions
Q13. Discuss the mechanism of electrophilic addition reactions of alkenes:
(a) Addition of HX (Markovnikov addition) — carbocation formation and stability
(b) Addition of halogens (Br₂, Cl₂) — formation of cyclic halonium ion intermediate
(c) Addition of water (acid-catalysed hydration)
(d) Anti-Markovnikov addition (peroxide effect and hydroboration-oxidation)
For each, show the mechanism using curved arrows and explain the regioselectivity.
Q14. Explain the following reactions of alkenes with mechanisms:
(a) Oxidation with cold dilute alkaline KMnO₄ (Baeyer's test) — syn dihydroxylation
(b) Oxidation with hot concentrated KMnO₄ — oxidative cleavage
(c) Ozonolysis — reductive and oxidative workup
(d) Catalytic hydrogenation using Ni, Pd, or Pt catalyst
Write the products for each reaction using propene and 2-methylbut-2-ene as examples.
Q15. Addition reactions of alkenes have transformed Indian industry and agriculture. Discuss:
(a) How hydration of ethene produces ethanol, which is blended with petrol (gasohol) in India
(b) Why catalytic hydrogenation of vegetable oils is used to produce vanaspati ghee in Indian households
(c) The use of ozonolysis in determining the structure of natural products and essential oils
(d) The role of anti-Markovnikov addition in synthesising important pharmaceuticals
Numerical / Application-Based Problems
Q16. An alkene (C₅H₁₀) on ozonolysis gives acetone (CH₃COCH₃) and acetaldehyde (CH₃CHO).
(a) Deduce the structure of the alkene.
(b) Write the balanced equation for the ozonolysis reaction.
(c) If 7.0 g of the alkene is subjected to ozonolysis, calculate the mass of acetone produced.
[Given: Molar masses: C₅H₁₀ = 70 g/mol, acetone = 58 g/mol]
Q17. The addition of HBr to 3-methyl-1-butene can give two products.
(a) Draw the structures of both possible products.
(b) Identify which product is formed by Markovnikov addition and which by rearrangement.
(c) Explain why a carbocation rearrangement occurs and draw the mechanism showing the hydride shift.
(d) Predict the major product and its percentage if the rearranged product is favoured 4:1 over the direct product.
Q18. A biodiesel plant in Pune produces ethanol by hydration of ethene. The plant processes 500 kg of ethene per day.
(a) Write the hydration reaction (acid-catalysed).
(b) Calculate the theoretical yield of ethanol.
(c) If the plant operates at 85% efficiency and sells ethanol at ₹ 55 per litre (density of ethanol = 0.789 g/mL), calculate the daily revenue.
[Given: Molar masses: C₂H₄ = 28 g/mol, C₂H₅OH = 46 g/mol]