-4
$\begingroup$

I have found various sources saying that ketones are acidic (pKa=20), and then relate it to the formation of the enolate ion. However, isn't an enolate ion of a ketone basic due to the oxygen's negative charge and all the pairs of electrons surrounding it?

$\endgroup$
  • 4
    $\begingroup$ If an acid loses its proton, it becomes a base and thus basic. $\endgroup$ – Jan Jul 3 '16 at 18:37
2
$\begingroup$

I think you need to recall the definition of an acid (in the Bronsted-Lowry scheme). An acid is a proton donor. A base is a proton acceptor. When a acid dissociates, it forms a hydrogen ion and the conjugate base of the acid. Remember, acid and base are only relative terms. The species which loses a proton in the reaction is acting as an acid and that which gains a proton is a base.

enter image description here

In the example above, the ketone is acting as an acid because it donates a proton. The hydride anion is acting a base because it accepts a proton. The resulting enolate anion is stabilised by delocalisation of the negative charge onto the oxygen. In the reverse reaction, the enolate would act as a base, accepting a proton from hydrogen (this is unlikely to happen though because the hydrogen will be liberated as a gas).

$\endgroup$
0
$\begingroup$

It will shift the places of the double bond and one of the hydrogen atoms, which will end up in a compound with a double bond between two of the carbon atoms.

That makes an enol which isn't as stable as a Ketone. The enol and Ketone are in a equilibrium which causes the enol to lose an hydrogen ion which then - the enol will become an enolate.

$\endgroup$
  • 1
    $\begingroup$ Enol formation is not required before the ketone can be deprotonated. Both routes yield the same result - an enolate ion. $\endgroup$ – bon Jul 3 '16 at 19:20

Your Answer

By clicking "Post Your Answer", you acknowledge that you have read our updated terms of service, privacy policy and cookie policy, and that your continued use of the website is subject to these policies.

Not the answer you're looking for? Browse other questions tagged or ask your own question.