# Why is the hydrogen adjacent to carbonyl carbon of aldehyde not acidic?

In $\ce{H^a-CH_2-CO-H^b}$, why is $\ce{H^a}$ more acidic than $\ce{H^b}$ ? From what I know, $\alpha$ hydrogen ($\ce{H^a}$) is highly acidic and is easily abstracted in presence of base $\ce{OH^-}$. But why is $\ce{H^b}$ not abstracted in the similar fashion?

$\ce{C}$ is electronegative because of the $+I$ effect it exerts on $\ce{O}$. Since, $\ce{H^b}$ is more nearer to the $\ce{C}$, shouldn't it be more acidic as the bond pair is more shifted towards the carbonyl carbon?

• The problem is that removal of H in the latter case causes resonance stabilization while in the other one it does not. – Sawarnik Apr 1 '17 at 19:41
• – Mithoron Apr 1 '17 at 20:15