Chemistry - GOC Question with Solution | TestHub
Addition of ammonia to a ketone (acetone). With the help of the HOMO-LUMO interaction involved, describe the trajectory of attack. The angle θ between the C=O bond axis and the approaching nucleophile (Burgi-Dunitz angle) is closest to :
Options:
Answer:
Solution:
The highest occupied molecular orbital (HOMO) of the nucleophile, which is the lone pair on the nitrogen atom of NH3, interacts with the lowest unoccupied molecular orbital (LUMO) of the carbonyl group, specifically the π* C=O orbital. The large lobe of this orbital is located on the carbon atom, perpendicular to the plane of the carbonyl group. Therefore, the nucleophile approaches from above the plane, rather than along the C=O axis. The optimal balance between maximizing orbital overlap and minimizing repulsion from the oxygen atom results in an approach angle of approximately 107°, known as the Bürgi-Dunitz angle.
Answer: (A)
