Chemistry Hydrocarbons MDCAT 2017
PMDC Verified Question 49 of 65
Among the following, which one has electron withdrawing effect:
A
\( -\text{NH}_2 \)
B
\( -\text{N}(\text{CH}_3)_2 \)
C
\( -\text{I} \)
D
\( -\text{CHO} \)
Tap any option to test your recall and reveal the step-by-step Propolis autopsy.

Propolis Cognitive Error Autopsy

Official Correct Choice:
Option D: \( -\text{CHO} \)
Concept:

Electron-withdrawing groups (EWG) usually possess atoms with a partial or full positive charge directly bonded to the ring, often due to multiple bonds with more electronegative atoms (like oxygen).

Solution:

  • The formyl group (\( -\text{CHO} \)) features a carbon atom double-bonded to a highly electronegative oxygen atom.


  • The oxygen pulls electron density away from the carbon, leaving it with a partial positive charge. This carbon, in turn, withdraws pi electron density from the benzene ring via resonance.


  • Hence, \( -\text{CHO} \) is a strong electron-withdrawing and ring-deactivating group.


Why other options are incorrect:

  • \( -\text{NH}_2 \) and \( -\text{N}(\text{CH}_3)_2 \) possess nitrogen atoms with a lone pair that can be donated into the ring via resonance, making them electron-donating groups (EDG).


  • Iodine (\( -\text{I} \)) withdraws electrons inductively but donates them via resonance. It is considered weakly deactivating but ortho/para directing. However, compared to \( -\text{CHO} \), the aldehyde group is fundamentally the definitive EWG via strong resonance.

Quality & Fidelity Assurance: Every question on BeambePrep is rigorously curated against the official PMDC syllabus with zero filler, zero out-of-syllabus content, and zero typos. When an authentic past paper originally contained a historical mistake or ambiguity from the examining board (such as UHS or NUMS), BeambePrep faithfully reflects the original paper while detailing the nuance and scientific consensus in the autopsy above.

Previous Question All Hydrocarbons MCQs Next Question

Want to solve full-length papers under timed exam conditions?

Practice with zero-scroll lockdown sprints, dynamic latency zone timers, live peer selection telemetry, and the automated Amber mistake recovery loop.

Enter Arena Sprint iOS App Android App