Question textThe figure shows a series of substituted anilines A-F, each with a different R-group in the para position to the NH2. For each molecule, indicate the electronic effect that the R group has on the benzene ring based on mesomeric and inductive effects. CH3 is known to be inductively electron donating, but has no mesomeric contribution. [table]
Compound | R group | Mesomeric Effect | Inductive Effect A | NO2 | Answer 1 Question 54 Electron WithdrawingElectron DonatingNone | Answer 2 Question 54 Electron WithdrawingElectron DonatingNone B | OMe | Answer 3 Question 54 Electron WithdrawingElectron DonatingNone | Answer 4 Question 54 Electron WithdrawingElectron DonatingNone C | NMe3+ | Answer 5 Question 54 Electron WithdrawingElectron DonatingNone | Answer 6 Question 54 Electron WithdrawingElectron DonatingNone D | CH3 | None | Electron Donating E | H | Answer 7 Question 54 Electron WithdrawingElectron DonatingNone | Answer 8 Question 54 Electron WithdrawingElectron DonatingNone F | CF3 | Answer 9 Question 54 Electron WithdrawingElectron DonatingNone | Answer 10 Question 54 Electron WithdrawingElectron DonatingNone
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Question

BlackTom AI · Accepted Answer

We are asked to indicate for each para substituent R the electronic effect on the benzene ring based on mesomeric (resonance) and inductive effects.
First, recall general rules:
- Electron-donating via mesomeric (R groups with lone pairs or π-donation) increase electron density in the ring (activating groups for electrophilic substitution in o/p positions).
- Electron-withdrawing via mesomeric effects pull electron density from the ring through resonance (often deactivating, or at least altering reactivity).
- Inductive effects reflect through-bond withdrawal or donation based on electronegativity and polarizability; strong electronegative substituents withdraw electron density inductively (-I), while alkyl groups typically donate slightly via inductive effects (+I in some contexts, but often considered electron-donating overall for substituent constants).
With that framework, evaluate each substituent:

A) NO2 (nitro group)
- Mesomeric effect: Electron Withdrawing. The NO2 group withdraws electron density from the ring by resonance, stabilizing negative charge but pulling electrons away from the ring in the conjugated system.
- Inductive effect: Electron Withdrawing. The nitro group is highly electronegative and pulls electron density through sigma bonds as well.

B) OMe (methoxy group)
- Mesomeric effect: Electron Donating. The lone pairs on oxygen can delocalize into the ring, increasing electron density via resonance.
- Inductive effect: Electron Withdrawing. The oxygen is electronegative and withdraws electron density through the sigma framework, though this effect is often weaker than the resonance donation.

C) NMe3+ (trimethylammonium substituent)
- Mesomeric effect: Electron Withdrawing. A positively charged nitrogen cannot donate electron density through resonance; its presence withdraws electron density from the ring via resonance as there is no available lone pair to push into the ring.
- Inductive effect: Electron Withdrawing. The positive charge on the substituent strongly pulls electron density through sigma bonds toward the substituent, reducing electron density on the ring.

D) CH3 (methyl group)
- Mesomeric effect: None. A simple alkyl group has no π-system to donate via resonance to the ring.
- Inductive effect: Electron Donating. Alkyl groups donate electron density slightly through sigma bonds, increasing ring electron density modestly.

E) H (hydrogen)
- Mesomeric effect: None. Hydrogen has no ability to donate or withdraw via resonance.
- Inductive effect: None. A hydrogen substituent does not perturb electron density through induction notably.

F) CF3 (trifluoromethyl group)
- Mesomeric effect: None. CF3 has no resonance donation or withdrawal via a π-system with the ring.
- Inductive effect: Electron Withdrawing. The highly electronegative fluorines withdraw electron density through sigma bonds, pulling electrons away from the ring.

Summary of each option in order:
- A (NO2): Mesomeric Effect = Electron Withdrawing; Inductive Effect = Electron Withdrawing
- B (OMe): Mesomeric Effect = Electron Donating; Inductive Effect = Electron Withdrawing
- C (NMe3+): Mesomeric Effect = Electron Withdrawing; Inductive Effect = Electron Withdrawing
- D (CH3): Mesomeric Effect = None; Inductive Effect = Electron Donating
- E (H): Mesomeric Effect = None; Inductive Effect = None
- F (CF3): Mesomeric Effect = None; Inductive Effect = Electron Withdrawing

CHEM0005_24-25 CHEM0005 2024-25 On-line Exam

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