enols

Problem # 741

Like enolates (Q740), enols can also act as nucleophiles and make new bonds at the alpha position.

Let's go through the mechanism for how this happens, using alpha bromination as our example.

In the reaction below, the carbonyl form is in equilibrium with its enol form (Q738), which can then attack molecular bromine.

 

Complete the structure of the protonated carbonyl, and show the curved arrows that transform it into the final carbonyl product.

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)

Problem # 738

Carbonyls are in equilibrium with their enol forms. This process is called keto-enol tautomerization.

This equilibrium happens in both acid and base.

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

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

 

a) Carbonyl to Enol (acidic)

 

b) Enol to Carbonyl (acidic)