a) Explain the mechanism of a nucleophilic attack on the carbonyl group of an aldehyde or a ketone.
b) An organic compound (A), molecular formula C₈H₁₆O₂, was hydrolysed with dilute sulphuric acid to give a carboxylic acid (B) and an alcohol (C). Oxidation of (C) with chromic acid also produced (B). On dehydration (C) gives but-2-ene. Write the equations for the reactions involved.
b) An organic compound (A), molecular formula C₈H₁₆O₂, was hydrolysed with dilute sulphuric acid to give a carboxylic acid (B) and an alcohol (C). Oxidation of (C) with chromic acid also produced (B). On dehydration (C) gives but-2-ene. Write the equations for the reactions involved.
Solution
(a) The nucleophile approaches the carbonyl carbon perpendicular to the molecular plane; as Nu–C forms, the π-pair moves to O giving the tetrahedral alkoxide, which is then protonated:
(b) C oxidises to the same acid B ⇒ C is the primary alcohol butan-1-ol (acid-catalysed dehydration gives but-1-ene, which isomerises to the more stable but-2-ene under HSO — as the paper states). B = butanoic acid; hence
(b) C oxidises to the same acid B ⇒ C is the primary alcohol butan-1-ol (acid-catalysed dehydration gives but-1-ene, which isomerises to the more stable but-2-ene under HSO — as the paper states). B = butanoic acid; hence
CBSE Class 12 Board · 2010 · Delhi · Subjective