Consider the following compounds (i) C6H5COCl (ii) [figure] (iii) [figure] (iv) [figure] The correct decreasing order of their reactivity towards hydrolysis is
- (i) > (ii) > (iii) > (iv)
- (iv) > (ii) > (i) > (iii)
- (ii) > (iv) > (i) > (iii)
- (ii) > (iv) > (iii) > (i)
Answer
(3) (ii) > (iv) > (i) > (iii)
Solution
Hydrolysis of an acyl chloride is a nucleophilic attack of H2O on the carbonyl carbon of –COCl.
⇒ Electron-withdrawing groups at the para position increase the positive charge on this carbon and increase the rate; electron-donating groups decrease it.
–NO2: strong –R and –I effect ⇒ most reactive (ii).
–CHO: –R and –I effect, weaker than –NO2 ⇒ (iv).
–H: reference ⇒ (i).
–CH3: +I effect and hyperconjugation ⇒ least reactive (iii).
∴ Order: (ii) > (iv) > (i) > (iii)
Answer: (3)