# Are hydrogen atoms in acetone molecule acidic?

My chemistry book says that acetone is aprotic, but I think that, since the conjugate base of acetone has possible resonating structures, the hydrogen atom must be free to move out as $\ce{H+}$ (as the resulting structure is more stable than the previous one). Where am I going wrong?

• What is the conjugate base of acetone? – DHMO Oct 24 '16 at 14:24
• There are levels upon levels of wholly different meanings to the word "acidic". Yes, acetone is acidic (in a way), but not like ordinary acids. And yes, it is aprotic. – Ivan Neretin Oct 24 '16 at 14:28
• Generally, we refer to protic as meaning "can hydrogen bond." This may be a bit of an oversimplification, but it might help you understand what the problem is here. – Zhe Oct 24 '16 at 14:29
• Why, you can, but it is pretty hard. – Ivan Neretin Oct 24 '16 at 14:33
• @ Ivan neretin , what makes it hard? – Pyro Recorcinol Oct 24 '16 at 14:34

$$\ce{H3C-C(=O)-CH3 <<=> H3C-C(-O^-)=CH2}$$
When compared with truly acidic compounds such as $\ce{HCl}$ and even $\ce{NH4+}$, acetone is a very, very weak acid, though. That does not mean it should be considered aprotic. Given a strong enough base — e.g. $\ce{HMDS}$ ($\ce{(Me3Si)2N-}$) — it can be deprotonated. Weaker bases will allow for partial (but probably hardly verifiable) deprotonations.
• @orthocresol Very good question! Somewhere between acetone and DMSO would be my guess so a $\mathrm{p}K_\mathrm{a}$ value of $25$~$35$. Toluene has ~$40$ so it’s definitely out. – Jan Oct 25 '16 at 13:16