Here's why:

* Acetone (CH3COCH3) has a carbonyl group (C=O). The oxygen atom in the carbonyl group is slightly electronegative, making it partially negative (δ-) and the carbon atom partially positive (δ+).

* Water (H2O) has two hydrogen atoms bonded to an oxygen atom. The oxygen atom is also electronegative, making it partially negative (δ-), and the hydrogen atoms partially positive (δ+).

Hydrogen bonding occurs when a partially positive hydrogen atom is attracted to a partially negative atom (usually oxygen, nitrogen, or fluorine). While the oxygen atom in acetone can accept hydrogen bonds from water molecules, the hydrogen atoms in acetone are not sufficiently positive to form strong hydrogen bonds with water's oxygen atom.

Therefore, the hydrogen bonding between acetone and water is weaker than the hydrogen bonding between water molecules. This is why acetone is somewhat soluble in water but not completely miscible.