between the two carboxyl groups (pKa ≈ 9–14). Loss of this acidic hydrogen atom produces a
carbanion, which is stabilized by the electron-withdrawing effect of both carboxyl groups, as shown
in Figure 8.6.
Figure 8.6. Acidity of the α-Hydrogen in β-Dicarboxylic Acids
Note that the α-hydrogen is less acidic than the hydroxyl hydrogens; the hydroxyl groups are left
protonated in this example for demonstration purposes only.KEY CONCEPT
The hydroxyl hydrogen is the most acidic proton on a carboxylic acid. However, in 1,3-
dicarbonyls, the α-hydrogen is also quite acidic.Note that this also applies to the α-hydrogens in a β-diketone, β-ketoacids, β-dialdehydes, and other
molecules that share the 1,3-dicarbonyl structure shown in Figure 8.7.
Figure 8.7. General Structure of 1,3-Dicarbonyl CompoundsMCAT Concept Check 8.1:
Before you move on, assess your understanding of the material with these questions.