Electromeric Effect DPP for NEET & JEE

Electromeric Effect DPP (NEET & JEE)

20 High-Yield PYQ-Based MCQs | JEE Main, Advanced & NEET Level

Electromeric Effect (E-effect) – Quick Recall:
• Temporary effect triggered by approach of reagent
• Complete transfer of π-electrons or lone pair
• +E: Electron release toward demand (e.g., in alkenes, carbonyls)
• –E: Electron withdrawal from demand (e.g., in carbocations)
• Reversible – disappears when reagent is removed
• Explains: Reactivity of C=C, C=O, electrophilic addition

1. [JEE Main 2023] The electromeric effect is:

a) Permanent
b) Temporary
c) Operates through σ bonds
d) Distance-independent

JEE Main 2023 | 11 April Shift 2

---

View Answer

Answer: b) Temporary

Explanation: E-effect is temporary and reagent-induced.
• Triggered when electrophile/nucleophile approaches
• Disappears after reaction
• Unlike inductive (permanent) or resonance (permanent)

2. [NEET 2022] In the reaction of alkene with HBr, the first step involves:

a) +E effect
b) –E effect
c) Inductive effect
d) Hyperconjugation

NEET 2022 Phase 1

---

View Answer

Answer: a) +E effect

Explanation: H⁺ (electrophile) approaches C=C → π-electrons shift toward H⁺ → +E effect
→ Forms carbocation → Br⁻ attacks (Markovnikov’s rule)

3. [JEE Adv 2021] The correct order of rate of hydration of alkenes is:

a) CH₂=CH₂ > CH₃–CH=CH₂ > (CH₃)₂C=CH₂
b) (CH₃)₂C=CH₂ > CH₃–CH=CH₂ > CH₂=CH₂
c) CH₂=CH₂ > (CH₃)₂C=CH₂ > CH₃–CH=CH₂
d) All equal

JEE Advanced 2021 Paper 1

---

View Answer

Answer: b) (CH₃)₂C=CH₂ > CH₃–CH=CH₂ > CH₂=CH₂

Explanation: Hydration via carbocation → stability ∝ rate.
• (CH₃)₂C=CH₂ → 3° carbocation → fastest
• Propene → 2°
• Ethene → 1°
+E effect helps π-electron shift to form stable carbocation.

4. [JEE Main 2024] The electromeric effect is observed in:

a) CH₃–CH₃
b) CH₂=CH₂
c) CH₃–Cl
d) CH₄

JEE Main 2024 | 4 April Shift 1

---

View Answer

Answer: b) CH₂=CH₂

Explanation: Requires π-bond or lone pair for electron displacement.
• Alkanes: only σ bonds → no E-effect
• CH₂=CH₂: π-bond → shows +E with H⁺, Br₂, etc.

5. [NEET 2023] The –E effect is shown by:

a) >C=O group with nucleophile
b) >C=O group with electrophile
c) C=C with H⁺
d) Lone pair on O in ether

NEET 2023

---

View Answer

Answer: a) >C=O group with nucleophile

Explanation: –E effect: Electrons move away from attacking reagent.
• Nucleophile (Nu⁻) attacks C=O → π-electrons shift to O → C becomes δ⁺ → –E

6. [JEE Adv 2020] In carbonyl compounds, the carbon is attacked by:

a) Nucleophiles due to +E effect
b) Electrophiles due to –E effect
c) Nucleophiles due to –E effect
d) Electrophiles due to +E effect

JEE Advanced 2020 Paper 2

---

View Answer

Answer: c) Nucleophiles due to –E effect

Explanation: Nu⁻ approaches C=O → π-electrons shift to O → C δ⁺ → –E effect
Example: NaBH₄, Grignard, CN⁻

7. [JEE Main 2022] The addition of HBr to unsymmetrical alkene follows:

a) Markovnikov rule due to +E effect
b) Anti-Markovnikov due to –E effect
c) Markovnikov due to inductive effect
d) No rule

JEE Main 2022 | 26 June Shift 1

---

View Answer

Answer: a) Markovnikov rule due to +E effect

Explanation: H⁺ adds to less substituted C → forms stable carbocation
• π-electrons shift toward H⁺ → +E effect
• Br⁻ adds to more substituted C

8. [NEET 2021] Electromeric effect is a:

a) Polarization effect
b) Delocalization effect
c) Temporary polarization
d) Permanent delocalization

NEET 2021

---

View Answer

Answer: c) Temporary polarization

Explanation: E-effect is temporary polarization of π-electrons or lone pair under reagent influence.

9. [JEE Adv 2019] The reactivity order of carbonyl compounds toward nucleophilic addition is:

a) HCHO > CH₃CHO > CH₃COCH₃ > (CH₃)₃CCOCH₃
b) (CH₃)₃CCOCH₃ > CH₃COCH₃ > CH₃CHO > HCHO
c) HCHO > (CH₃)₃CCOCH₃ > CH₃CHO > CH₃COCH₃
d) All equal

JEE Advanced 2019 Paper 1

---

View Answer

Answer: a) HCHO > CH₃CHO > CH₃COCH₃ > (CH₃)₃CCOCH₃

Explanation: Reactivity ∝ ease of –E effect (π-shift to O)
• HCHO: no +I → highest δ⁺ on C
• Alkyl groups: +I → reduce δ⁺ → slower Nu attack

10. [JEE Main 2025] The compound that does NOT show electromeric effect is:

a) CH₂=CH–Cl
b) CH₃–CH=CH₂
c) CH₃–CH₂–Cl
d) CH₃–CHO

JEE Main 2025 | Predicted PYQ

---

View Answer

Answer: c) CH₃–CH₂–Cl

Explanation: No π-bond or lone pair on Cl for complete shift.
• CH₃–CH₂–Cl: only inductive effect
• Others have π-system → show E-effect

11. [JEE Adv 2022] In which reaction is +E effect predominant?

a) Addition of CN⁻ to acetone
b) Addition of H⁺ to propene
c) Halogenation of benzene
d) Nitration of phenol

---

View Answer

Answer: b) Addition of H⁺ to propene

Explanation: H⁺ (electrophile) → π-electrons move toward it → +E effect

12. [NEET 2020] The electrophilic addition to alkene is initiated by:

a) Nucleophile
b) Electrophile
c) Free radical
d) Carbene

---

View Answer

Answer: b) Electrophile

Explanation: Triggers +E effect → π-electrons shift → carbocation → nucleophile adds.

13. [JEE Main 2021] The correct statement about electromeric effect is:

a) It is reversible
b) It operates in saturated compounds
c) It is stronger than inductive effect
d) It increases with distance

---

View Answer

Answer: a) It is reversible

Explanation: E-effect appears only during reaction and vanishes afterward.

14. [JEE Adv 2018] The slowest step in nucleophilic addition to carbonyl is:

a) Approach of nucleophile
b) Formation of tetrahedral intermediate
c) Collapse of intermediate
d) Protonation

---

View Answer

Answer: b) Formation of tetrahedral intermediate

Explanation: Requires –E effect and breaking of π-bond → highest energy barrier.

15. [NEET 2019] The +E effect is shown by:

a) C=C with Br₂
b) C=O with H⁺
c) Lone pair on N in amine
d) C≡C with H⁺

---

View Answer

Answer: a) C=C with Br₂

Explanation: Br⁺ approaches → π-electrons shift → +E effect

16. [JEE Main 2020] The compound most reactive toward electrophilic addition is:

a) Ethene
b) Propene
c) 2-Methylpropene
d) 2-Butene

---

View Answer

Answer: c) 2-Methylpropene

Explanation: Forms 3° carbocation → fastest +E effect and stabilization.

17. [JEE Adv 2023] In which case is –E effect NOT involved?

a) Hydration of alkene
b) Hydrolysis of ester
c) Addition of HCN to acetone
d) Ozonolysis of alkene

---

View Answer

Answer: d) Ozonolysis of alkene

Explanation: Ozonolysis is cycloaddition → no carbocation → no E-effect.
Others involve Nu attack on C=O or H⁺ on C=C → –E or +E.

18. [NEET 2024] The electromeric effect is maximum in:

a) Conjugated systems
b) Isolated double bonds
c) Saturated compounds
d) Aromatic rings

---

View Answer

Answer: a) Conjugated systems

Explanation: Extended π-system → easier electron displacement → stronger E-effect.

19. [JEE Main 2019] The reaction showing +E effect is:

a) CH₃MgBr + CH₃CHO
b) CH₂=CH₂ + H⁺
c) CH₃COOH + NaOH
d) CH₃Cl + AgNO₃

---

View Answer

Answer: b) CH₂=CH₂ + H⁺

Explanation: H⁺ attacks → π-electrons move toward it → +E effect

20. [JEE Adv 2024] The order of reactivity of carbonyl compounds toward NaBH₄ is:

a) Formaldehyde > Acetaldehyde > Acetone > Pivaldehyde
b) Pivaldehyde > Acetone > Acetaldehyde > Formaldehyde
c) Acetone > Formaldehyde > Acetaldehyde > Pivaldehyde
d) All equal

---

View Answer

Answer: a) Formaldehyde > Acetaldehyde > Acetone > Pivaldehyde

Explanation: NaBH₄ → H⁻ (Nu) attacks C=O → –E effect
• HCHO: no +I → highest δ⁺ → fastest
• (CH₃)₃CCOCH₃: bulky + +I → slowest