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Class 11  Β»  Chemistry  Β»  Organic Chemistry Basic Principles

Electromeric Effect - UNSOLVED PRACTICE SET

Class 11

Chapter: Organic Chemistry Basic Principles | Topic: Electromeric Effect

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Study Material.
Class 11

ELECTROMERIC EFFECT - UNSOLVED PRACTICE SET

Topic: Electromeric Effect

Time: 40 mins | Marks: 30 | Difficulty: Medium

Multiple Choice Questions

Q1. The electromeric effect is:

  1. A permanent effect involving Οƒ electrons
  2. A temporary effect involving Ο€ electrons in the presence of an attacking reagent
  3. A permanent effect involving Ο€ electrons
  4. A temporary effect involving Οƒ electrons

Q2. The electromeric effect is shown by:

  1. Only saturated compounds
  2. Only unsaturated compounds containing multiple bonds
  3. Both saturated and unsaturated compounds
  4. Only ionic compounds

Q3. In the +E effect, the Ο€ electrons move:

  1. Away from the attacking reagent
  2. Towards the attacking reagent
  3. In a circular motion
  4. Nowhere; they remain fixed

Q4. When a nucleophile attacks the carbonyl carbon of acetone, the electromeric effect causes:

  1. The C=O bond to become stronger
  2. The Ο€ electrons of C=O to move towards oxygen, making carbon electron-deficient
  3. The Ο€ electrons to move towards carbon
  4. No change in electron distribution

Q5. The electromeric effect:

  1. Operates in the ground state of the molecule
  2. Operates only in the excited state or during a reaction
  3. Is independent of the attacking reagent
  4. Is the same as the inductive effect

Q6. Which of the following compounds will show the +E effect when attacked by an electrophile?

  1. CHβ‚‚=CHβ‚‚
  2. CH₃–CH₃
  3. CHβ‚„
  4. Cβ‚‚H₆

Short Answer Questions

Q7. Define electromeric effect. How does it differ from the inductive effect and the mesomeric effect?

Q8. Explain the +E and –E effects with one example each. What determines whether a molecule shows +E or –E effect?

Q9. Draw the mechanism showing the electromeric effect in ethene when attacked by H⁺ (electrophile). Show the movement of Ο€ electrons.

Q10. Why does the carbonyl carbon in aldehydes and ketones become electrophilic during nucleophilic addition reactions? Explain using the electromeric effect.

Q11. Your teacher demonstrates that propene reacts with HBr to give 2-bromopropane as the major product. Explain how the electromeric effect helps predict this regioselectivity.

Q12. How does the electromeric effect differ from the inductive effect with respect to:

(a) The type of electrons involved

(b) The duration of the effect

(c) The presence of an attacking reagent

Long Answer Questions

Q13. Discuss the electromeric effect in detail:

(a) Definition and conditions for the electromeric effect

(b) +E effect β€” movement of Ο€ electrons towards the attacking reagent

(c) –E effect β€” movement of Ο€ electrons away from the attacking reagent

(d) Difference between electromeric effect and other electronic effects (inductive, mesomeric)

(e) Importance of the electromeric effect in predicting reaction mechanisms

Q14. Explain the role of the electromeric effect in the following reactions:

(a) Electrophilic addition of HBr to propene (Markovnikov's rule)

(b) Nucleophilic addition to carbonyl compounds (aldehydes and ketones)

(c) Electrophilic aromatic substitution in benzene

For each reaction, show the movement of electrons using curved arrow notation.

Q15. The electromeric effect is crucial in understanding reaction mechanisms in organic chemistry. Discuss:

(a) Why the +E effect in alkenes makes them susceptible to electrophilic attack

(b) How the –E effect in carbonyl compounds directs nucleophiles to the carbonyl carbon

(c) The role of the electromeric effect in the design of organic solar cells being researched in India

(d) Why understanding the electromeric effect helps predict the products of competitive reactions

Numerical / Application-Based Problems

Q16. Consider the reaction of propene (CH₃–CH=CHβ‚‚) with HBr.

(a) Draw the two possible carbocation intermediates formed after the initial electrophilic attack by H⁺.

(b) Using the concept of hyperconjugation and inductive effect, determine which carbocation is more stable.

(c) Predict the major product and explain why Markovnikov's rule operates.

Q17. In the nucleophilic addition of HCN to acetone ((CH₃)β‚‚C=O):

(a) Show the electromeric effect using curved arrows when CN⁻ attacks the carbonyl carbon.

(b) Draw the tetrahedral intermediate formed.

(c) Explain why the reaction is catalysed by base but inhibited by acid (excess H⁺).

Q18. A research team in Pune is studying the reaction of but-2-ene with bromine (Brβ‚‚).

(a) Show the step-by-step mechanism using the electromeric effect, including the formation of the cyclic bromonium ion intermediate.

(b) Explain why the addition is anti (trans) rather than syn (cis).

(c) If the reaction is carried out in the presence of NaCl, predict what other product might form and explain why.


Total: 30 Marks | Time: 40 mins

Explore more topics in Organic Chemistry Basic Principles

Classification of Organic Compounds Nomenclature IUPAC Rules Isomerism Structural and Stereoisomerism Hybridisation in Organic Molecules Inductive Effect Resonance and Mesomeric Effect Hyperconjugation Homolytic and Heterolytic Fission Types of Reagents Electrophile Nucleophile Types of Reactions Substitution Addition Elimination