91Ó°ÊÓ

Diketones have two different sets of alpha-hydrogens. They can potentially form products with different membered rings, e.g., 3-membered, 4-membered, 5-membered,6-membered, etc.

The greater stability of the rings, it draws the equilibria towards its formation; therefore, the products with the more stable ring is the only product formed from the intramolecular aldol addition reactions.

2,4-pentanedione does not undergo an intramolecular addition reaction because if it does so it will form a strained four-membered ring of 3-hydroxy-3 -methylcyclobutanone.

Therefore 2,4-pentanedione undergoes an intermolecular reaction in which the removal of a proton from more acidic central carbon leads to the formation of a product 3-acetyl-4-hydroxy-4-methyl heptane-2,6-dione.

The formation of intermolecular product over intramolecular product is shown as follows:

Formation of intermolecular product