Rank the bold-faced hydrogens for the following compounds from most acidic to least acidic.
A)I IV II V III
B)II I IV V III
C)V III II I IV
D)IV I II V III
E)IV II I V III

Question

Rank the bold-faced hydrogens for the following compounds from most acidic to least acidic. 
A)I > IV > II > V > III 
B)II > I > IV > V > III 
C)V > III > II > I > IV 
D)IV > I > II > V > III 
E)IV > II > I > V > III

Quizplus · Accepted Answer

The most acidic hydrogen will be the one that is most likely to dissociate from the molecule and form a hydronium ion. This is typically the hydrogen that is attached to the most electronegative atom or the one that is located on the most stable anion. In this case, the carbonyl group in compound IV is the most electronegative atom and also forms the most stable anion (the enolate). Therefore, the hydrogen attached to the carbonyl group in compound IV is the most acidic. The order of acidity is therefore IV > I > II > V > III, which is given by choice D.

Rank the Bold-Faced Hydrogens for the Following Compounds from Most