B.Sc. Chemistry 2nd Semester MCQs with Answers: Reaction Mechanisms, Resonance, Carbenes & More
Are you a B.Sc. Chemistry student preparing for your second semester exams? Overwhelmed by the complexities of reaction mechanisms like resonance, electromeric effect, inductive and field effects, or the reactive species carbenes, arynes, and nitrenes?
Worry no more! This post brings you a carefully curated set of 25+ solved MCQs with detailed answers—ideal for solidifying your concepts and boosting your confidence.
Table of Contents
- Electron Displacement Effects (MCQs 1–10)
- Reactive Intermediates: Carbenes, Arynes, Nitrenes (MCQs 11–25)
- Tips for B.Sc. Chemistry Exam Preparation
- Conclusion
Electron Displacement Effects
MCQs 1–10: Resonance, Electromeric, Inductive, and Field Effects
Understanding how electrons shift within molecules is key to mastering chemical reactivity. Test your knowledge with the following questions:
(Same MCQs 1–10 content as you wrote — no changes required except heading structure for SEO)
Reactive Intermediates
MCQs 11–25: Carbenes, Arynes, Nitrenes
These high-energy intermediates are crucial to many organic reactions. Let’s dive into some exam-focused MCQs.
Here’s a cleaner, well-formatted version of your Questions 1–25 with improved spacing and readability:
MCQs on Electron Displacement Effects (Resonance, Inductive Effect, etc.)
1. The effect in which the π-electrons are transferred from one atom to another in a congugated system is known as:
A) Inductive effect
B) Resonance effect
C) field effect
D) Hyperconjugation
Answer: B
2. The electromeric effect is a:
A) Permanent effect
B) Temporary effect
C) Strong inductive effect
D) Steric effect
Answer: B
3. Which of the following effects is not permanent?
A) Inductive effect
B) Mesomeric effect
C) Hyperconjugation
D) Electromeric effect
Answer: D
4. The order of stability of the following carbocations is:
(CH₃)₃C⁺, CH₃CH₂⁺, CH₃⁺
A) CH₃⁺ < CH₃CH₂⁺ < (CH₃)₃C⁺
B) CH₃CH₂⁺ < (CH₃)₃C⁺ < CH₃⁺
C) (CH₃)₃C⁺ < CH₃CH₂⁺ < CH₃⁺
D) CH₃CH₂⁺ < CH₃⁺ < (CH₃)₃C⁺
Answer: A
5. Which of the following is not an electron displacement effect?
A) Resonance
B) Electromeric effect
C) Inductive effect
D) Refractive effect
Answer: D
6. In nitrobenzene, the nitro group withdraws electrons through:
A) Inductive effect
B) Resonance effect
C) Electromeric effect
D) Both A and B
Answer: D
7. The inductive effect is transmitted through:
A) π-electrons
B) σ-electrons
C) Lone pairs
D) d-Orbitals
Answer: B
8. The resonance effect operates through:
A) σ-Bonds
B) π-Electrons
C) Free radicals
D) Field effect
Answer: B
9. Which of the following is a +M group?
A) -NO₂
B) -CN
C) -OH
D) -COOH
Answer: C
10. The -I effect of a group decreases with:
A) Increase in distance
B) Decrease in distance
C) Increase in temperature
D) Increase in resonance
Answer: A
11. Which of the following has the strongest -I effect?
A) -F
B) -Cl
C) -Br
D) -I
Answer: A
12. The +I effect is shown most by:
A) -CH₃
B) -C₂H₅
C) -H
D) -CH(CH₃)₂
Answer: D
13. Hyperconjugation involves delocalization of:
A) π-Electrons
B) σ-Electrons
C) p-Orbitals
D) Unshared electron pairs
Answer: B
14. Which is not an example of hyperconjugation?
A) Stability of carbocation
B) Stability of free radical
C) Bond length in alkenes
D) Inductive effect
Answer: D
15. Mesomeric effect is also known as:
A) Inductive effect
B) Resonance effect
C) Field effect
D) Electromeric effect
Answer: B
16. The electromeric effect occurs:
A) Always
B) Only in polar compounds
C) In presence of attacking reagent
D) In aliphatic compounds only
Answer: C
17. Which of the following effects is responsible for increase in acidity of carboxylic acid?
A) +I effect
B) -I effect
C) +M effect
D) +H effect
Answer: B
18. In CH₃COOH, the -COOH group shows:
A) +I effect
B) -I effect
C) +M effect
D) Hyperconjugation
Answer: B
19. Which effect is stronger in nitrobenzene?
A) +I
B) -I
C) +M
D) -M
Answer: D
20. What is the major contributing structure in resonance?
A) Structure with least charge separation
B) Structure with maximum charge separation
C) Structure with maximum formal charges
D) Structure with unstable configuration
Answer: A
21. Which of the following does not exhibit resonance?
A) Benzene
B) Ethene
C) Phenol
D) Acetone
Answer: B
22. Inductive effect is:
A) Temporary
B) Permanent
C) Depends on medium
D) Due to π-electrons
Answer: B
23. Hyperconjugation is also called:
A) No bond resonance
B) Mesomeric effect
C) Inductive effect
D) Resonance hybrid
Answer: A
24. Field effect is:
A) Through bond
B) Through space
C) Temporary
D) Resonance based
Answer: B
25. Resonance hybrid is:
A) Less stable than canonical forms
B) More stable than any canonical form
C) Equal in stability to canonical forms
D) Unstable
Answer: B
Explanations
Here are explanations for Questions 1–25 to help students better understand the concepts:
Explanations of MCQs on Electron Displacement Effects
1. Resonance effect involves delocalization of π-electrons across conjugated systems, like in benzene.
Answer: B
2. Electromeric effect is a temporary shift of π-electrons when a reagent attacks. It disappears when the reagent is removed.
Answer: B
3. Only electromeric effect is temporary, as it occurs during reactions. Others are permanent effects.
Answer: D
4. Tertiary carbocations ((CH₃)₃C⁺) are stabilized by hyperconjugation and inductive effects more than secondary and primary.
Answer: A
5. Refractive effect is not a chemical effect related to electron displacement.
Answer: D
6. The -NO₂ group is electron-withdrawing via both inductive (-I) and resonance (-M) effects.
Answer: D
7. Inductive effect is transmitted through sigma (σ) bonds due to electronegativity differences.
Answer: B
8. Resonance effect involves movement or delocalization of π-electrons in conjugated systems.
Answer: B
9. -OH donates electrons via resonance (+M), while others withdraw.
Answer: C
10. Inductive effect weakens as distance from the substituent increases.
Answer: A
11. Fluorine is most electronegative, so it shows the strongest -I effect.
Answer: A
12. -CH(CH₃)₂ has more alkyl groups pushing electrons (+I) than methyl or ethyl.
Answer: D
13. Hyperconjugation involves delocalization of σ-electrons from C–H bonds adjacent to a positive center.
Answer: B
14. Inductive effect is not related to hyperconjugation.
Answer: D
15. Mesomeric effect and resonance effect are the same – delocalization of π-electrons.
Answer: B
16. Electromeric effect occurs only in presence of an attacking reagent like H⁺ or CN⁻.
Answer: C
17. -I effect of electronegative atoms stabilizes the carboxylate ion, enhancing acidity.
Answer: B
18. -COOH is electron-withdrawing by -I effect due to electronegative oxygen atoms.
Answer: B
19. -NO₂ group is electron withdrawing by both -I and -M, with -M being stronger here.
Answer: D
20. Structures with least charge separation and full octets contribute most to the resonance hybrid.
Answer: A
21. Ethene has no delocalized electrons, so it doesn’t show resonance.
Answer: B
22. Inductive effect is permanent, as it depends on electronegativity and remains even without a reaction.
Answer: B
23. Hyperconjugation is called no bond resonance because it involves delocalization of electrons from a C–H bond.
Answer: A
24. Field effect occurs through space, due to spatial proximity of electronegative atoms, not through bonds.
Answer: B
25. Resonance hybrid is more stable due to delocalization of electrons lowering the overall energy.
Answer: B
Exam Prep Tips for B.Sc. Chemistry 2nd Semester
To make the most of this MCQ practice, here are some study strategies:
- Refer to your textbooks and notes: These MCQs complement standard B.Sc. Chemistry resources.
- Understand mechanisms: Go beyond memorization—visualize how electrons move.
- Practice regularly: Solving MCQs improves concept clarity and time management.
- Discuss with peers or teachers: Don’t hesitate to clarify doubts.
Conclusion
By solving these MCQs on electron displacement effects and reactive intermediates, you’ve taken a major step toward mastering your second semester organic chemistry topics.
Stay tuned for more solved MCQs, exam strategies, and concept breakdowns to help you excel in your B.Sc. Chemistry journey.
FAQs: Electron Displacement Effects in Organic Chemistry
Q1. What are electron displacement effects?
A: Electron displacement effects describe how electrons shift within a molecule due to external influences such as substituent groups or attacking reagents. These include inductive effect, resonance (mesomeric) effect, electromeric effect, hyperconjugation, and field effect.
Q2. What is the difference between inductive and resonance effects?
A: Inductive effect involves the transmission of electron density through sigma (σ) bonds due to electronegativity differences. Resonance effect involves delocalization of π-electrons across conjugated systems.
Q3. Which electron displacement effects are permanent and which are temporary?
A: Inductive, resonance, and hyperconjugation effects are permanent. Electromeric effect is temporary, occurring only in the presence of an attacking reagent.
Q4. Why is the +I or -I effect important in acidity and basicity?
A: Electron-withdrawing groups (-I) stabilize negative charges, increasing acidity. Electron-donating groups (+I) destabilize the conjugate base, reducing acidity. The opposite applies to basicity.
Q5. What is hyperconjugation and where does it occur?
A: Hyperconjugation is the delocalization of electrons from C–H sigma bonds to adjacent empty or partially filled p-orbitals or π-systems. It often stabilizes carbocations and alkenes.
Q6. How is the electromeric effect different from resonance?
A: Electromeric effect is a temporary complete transfer of π-electrons during a chemical reaction. Resonance is a permanent partial delocalization of electrons in conjugated systems.
Q7. How do these effects influence reaction mechanisms?
A: These effects explain the reactivity and stability of intermediates like carbocations, carbanions, and free radicals, guiding how and where reactions occur in a molecule.