Which of the following aldehydes is less reactive towards nucleophilic addition reaction?

Which of the following aldehydes is less reactive towards nucleophilic addition reaction?
  1. Benzaldehyde
  2. Formaldehyde
  3. Acetaldehyde
  4. Butyraldehyde

Solution

Reactivity for N.A.R $\propto$ Attack of Nucleophile. $\propto$ +ve charge on $\mathrm{sp}^2$-carbon $\propto \frac{1}{\text { Steric hindrance }}$ $\propto \frac{-\mathrm{M}|-\mathrm{H}|-\mathrm{I}}{+\mathrm{M}|+\mathrm{H}|+\mathrm{I}}$ $\frac{\mathrm{HCHO}>\mathrm{CH}_3-\mathrm{CHO}>\mathrm{CH}_3-\mathrm{CH}_2-\mathrm{CH}_2 \mathrm{CHO}>\mathrm{C}_6 \mathrm{H}_5-\mathrm{CHO}}{\text { Reactivity in decreasing order }}$

Asked in: MHT CET 2021 (24 Sep Shift 2)

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