Fundamentals of Organic ChemistryChemistryAldehydes and Ketones
Choose the correct order of increasing reactivity with NaBH ₄ for the following carbonyl compounds: (i) (ii) (iii)
Options
- A(ii) < (i) < (iii)
- B(i) < (iii) < (ii)
- C(i) < (ii) < (iii)
- D(iii) < (i) < (ii)
Correct answer
D. (iii) < (i) < (ii)
Step-by-step solution
The reactivity of carbonyl compounds towards nucleophilic addition (such as reduction by NaBH₄ ) depends on the magnitude of the positive charge on the carbonyl carbon and the steric hindrance around it. 1. Ketones are generally less reactive than aldehydes due to greater steric hindrance from two alkyl groups and their electron-donating +I effect, which decreases the electrophilicity of the carbonyl carbon. Thus, acetone (iii) is the least reactive. 2. Between the two aldehydes, acetaldehyde (i) has a methyl group