Concept:Reactivity of carbonyl compounds toward nucleophilic attack decreases as steric hindrance (bulkiness) and electron-donating inductive effects increase.
Solution:- Methanal (\( H-CO-H \)): Has two tiny hydrogen atoms. Minimum steric hindrance and no electron-donating alkyl groups. Most reactive.
- Aldehydes (\( H-CO-R \)): Have one bulky, electron-donating alkyl group (R). The carbon is slightly less positive and slightly more blocked. Intermediate reactivity.
- Ketones (\( R-CO-R \)): Have two bulky, electron-donating alkyl groups. The carbon is sterically crowded and electronically stabilized. Least reactive.
- Therefore, the correct decreasing order of reactivity is: \( H-CO-H > H-CO-R > R-CO-R \).
Why other options are incorrect:Options A and B incorrectly rank ketones as more reactive than aldehydes. Option D incorrectly ranks ketones as more reactive than substituted aldehydes.
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.