> See also: > - Reference # Enols and Enolates > [!summary] Summary > Enols and enolates are ... ![[Enols and Enolates-3.png]] ## Enols An **enol** is a compound containing a *hydroxyl group (OH) connected directly to a carbon-carbon double bond.* > [!important]+ **Acid-Catalyzed & Base-Catalyzed Tautomerization** > Enols can be formed by treating a ketone with a *catalytic acid/base*: > > **Acid-Catalyzed Tautomerization** > > ![[Enols and Enolates-4.png]] > > 1. **Proton Transfer:** the *carbonyl group* is *protonated* to form a [[Resonance Structures|resonance-stabilized]] *cation*. (Remember that [[Stability of Carbocations|tertiary carbocations]] are the most stable) > 2. **Proton Transfer:** the $\alpha$ carbon is *deprotonated* leading to a *C=C double bond* forming and thus the enol product. > > --- > **Base-Catalyzed Tautomerization** > > ![[Base-Catalyzed Tautomerization.png]] > > 1. **Proton Transfer:** the $\alpha$ carbon is *deprotonated* to form a [[Resonance Structures|resonance-stabilized]] *anion* intermediate > 2. **Proton Transfer:** the negatively charged oxygen is *protonated* ### Tautomerization and Equilibrium ![[Alpha Carbon Chemistry.png|200]] Enols/enolates and ketones are considered **tautomers** as they are [[Isomers|constitutional isomers]] that *rapidly "interconvert"* through the *migration of a proton*. It's important to note that this is **not a difference of resonance**, the ketone and enol/enolates are in fact *different compounds* that are in *equilibrium* with each other. Unless extremely rare conditions are employed, you should *always assume that tautomerization will occur if possible*, and an equilibrium will quickly be established favoring the *more stable tautomer*. In most cases, the *enol will be the less favored* product of the [[Chemical Equilibria|equilibrium]] and the original ketone will be the major product: ![[Enols and Enolates.png|200]] However, in other cases, the *formation of the enol can lead to a more stable product*, causing it to become more favored as a result: ![[Enols and Enolates-5.png|200]] ## Enolates When treated with a *strong base*, the $\alpha$ position of a ketone is deprotonated to give a resonance stabilized intermediate known as an **enolate**: ![[Enols and Enolates-6.png]] Because of this resonance, there are two [[nucleophilic]] (electron-rich) sites that are reactive. - When the *$\alpha$ carbon serves as the nucleophile*, it is called a **C-attack**, - When the *oxygen is serving as the nucleophile*, it is called an **O-attack**. ![[Enols and Enolates-7.png]] Despite the negative oxygen atom being the favored resonance structure, the **C-attack** is more reactive. --- **Enolates** are considered more useful than **enols** because: 1. *Enolates possess a full negative charge* and are therefore more reactive than enols. 2. *Enolates can be isolated and stored* for short periods of time, unlike enols which typically cannot be isolated or stored. ### Choosing a Base for Enolate Formation ## Aldol Condensation ![[Enols and Enolates-2.png]]