Chemistry - GOC Question with Solution | TestHub
Addition of water to a ketone. With the help of the HOMO-LUMO interaction involved, describe the trajectory with which the water molecule approaches the carbonyl group, and explain why the approach angle is not 90°. The approach angle of the nucleophile to the C=O axis (Bürgi-Dunitz trajectory) is about :
Options:
Answer:
Solution:
The HOMO of the nucleophile (a lone pair on the oxygen of H2O) interacts with the LUMO of the carbonyl group (the π* orbital of the C=O bond). The best overlap is achieved when the nucleophile approaches the carbonyl carbon along the Bürgi-Dunitz trajectory, at an angle of about 107° to the C=O axis (as shown). The angle is not 90° because an approach perpendicular to the carbonyl plane is repelled by the high electron density on the carbonyl oxygen; the nucleophile therefore comes in tipped away from the oxygen.
Answer: (A).
