Problem 739

Problem # 739

Carbonyls are in equilibrium with their enol forms. An enolate is the deprotonated form of an enol.

Enolates are formed from carbonyls under basic conditions.

Let's go through this equilibrium under basic conditions. Draw a mechanism using curved arrows for each reaction below.

Remember that under basic conditions, most species are either neutral or negatively charged, and rarely positively charged. So your structures will contain either ROH or RO^-, but not ROH₂⁺.

a) Carbonyl to Enolate (basic)

b) Enolate to Carbonyl (basic)

Solution

These mechanisms are similar to those in problem 738, only under basic conditions.

a) Carbonyl to Enolate (basic)

In the mechanism below the carbonyl was deprotonated at the alpha position, and the enolate was then drawn as a resonance form. You can also go straight from carbonyl to enolate in one reaction arrow. (rip off the proton, form the new double bond, and send the carbonyl "up" to form a negative charged oxygen).

b) Enolate to Carbonyl (basic) "DOWN"

Like a), this reaction can be done in one reaction arrow (negative charge comes "down" and double bond attacks a proton)

It's important that you become familiar with the mechanisms for enol and enolate formation in both acid (Q738) and in base (this problem), as well as carbonyl hydrate formation in both acid (Q706) and base (Q705).

If you can draw these four mechanisms you will be able to figure most of the reactions in second semester organic chemistry!

Problem Details

MendelSet practice problem # 739 submitted by Matt on July 27, 2011.