Arrange the following compounds in decreasing order of the acidity of their most acidic protons: (I) (II) (III)

Step-by-step solution

The acidity of the given compounds is determined by the stability of their respective conjugate bases formed after the removal of the most acidic proton. Compound (III) is dimethyl malonate. Its most acidic protons are the methylene protons between the two carbonyl groups. The resulting carbanion is highly stabilized by resonance delocalization over two ester carbonyl groups, making it the most acidic ( pK_a 13 ). Compound (I) is acetaldehyde. Its conjugate base is stabilized by resonance with one aldehyde carbonyl