Experimentally, it has been found that alpha-hydrogens are more acidic than the aldehyde hydrogen. We can witness this situation in aldol c...
Experimentally, it has been found that alpha-hydrogens are more acidic than the aldehyde hydrogen. We can witness this situation in aldol condensation reactions between a ketone and an aldehyde. In this reaction a base removes an alpha-hydrogen from the ketone and not the aldehyde hydrogen. But, how can we explain this observation theoretically?
Well, we can explain it in terms of the resonance stabilization of the conjugate base.
For example, consider the conjugate base of the ketone and the aldehyde below.
Notice that it is possible to draw resonance structures for the conjugate base of the ketone. However, we cannot say the same for the conjugate base of the aldehyde.
Since the conjugate base of the ketone has resonance structures, the alpha-proton is more likely to be removed (by a base) because the resulting species (conjugate base) will be able to stabilize the negative charge.
You can think of that like if the molecule does not mind that much to donates a proton because it still can be so what stable.
Species that can stabilize a negative charge, after losing a proton, are more acidic than those that cannot provide a stabilization.
