Arrange the following carbonyl compounds in decreasing order of their rate of reduction by NaBH ₄ : (i) (ii) (iii) (iv)

Step-by-step solution

The rate of reduction of carbonyl compounds by NaBH₄ depends on the electrophilicity of the carbonyl carbon and the steric hindrance around it. Aldehydes are generally more reactive than ketones towards nucleophilic addition because they have less steric crowding and only one electron-donating group attached to the carbonyl carbon. Therefore, the aldehydes (i) and (iv) are more reactive than the ketones (ii) and (iii). Comparing the aldehydes (i) and (iv), compound (iv) is 4-nitrobenzaldehyde. The -NO₂ group is str