This document discusses enols and enolates. Enols are formed when a carbonyl compound loses its alpha proton, forming an anion called an enolate that is stabilized by delocalization. Keto-enol tautomerism allows easy interconversion between keto and enol forms using acid or base. Enolates such as lithium enolates and silyl enolates are stable equivalents that can undergo reactions like halogenation, the haloform reaction, malonic ester synthesis, and alkylation. Thermodynamic enolates predominate under equilibrium while kinetic enolates form fastest with hindered bases. Reactions of enolates include acid/base-catalyzed

1. Enol and Enolates
Presented by: Rizwana Sarwar
Presented to: Dr. Imran Ali Hashmi
Dr. Firdos
Dr. Samreen

2. Contents
1. Enol and Enolates
2. Keto Enol Toutomarism
3. Stable Enol Equivelents
4. Synthsis of Enolates
5. Thermodynamic and Kinetic Enolates
6. Reaction of Enolates

3. What are Enol and
Enolates?
• The carbonyl group is strongly electron withdrawing.
• When a carbonyl compound loses α proton, the anion
that is produced, called an enolate.
• It is stabilized by delocalization.
• The Term Enol is used because of C=C ene and -OH ol.

4. Keto Enol Tautomers
• The keto and enol forms of carbonyl compounds are constitutional
isomers.
• They are easily interconverted by proton transfers in the presence of
an acid or base.
• Interconvertible keto and enol forms are called tautomers, and
their interconversion is called Tautomerization.

5. Keto Enol Tautomers
• In compounds whose molecules have two carbonyl groups.
• The amount of enol present at equilibrium is far higher.
• The greater stability of the enol form of β-dicarbonyl compounds is
due to hydrogen bonding.

6. Acid catalyzed Enolization

7. Base catalyzed Enolization

8. Some Enol Equivelents
• Lithium Enolates
• Silyl Enolates
• Aza Enolates

9. Thermodynamic and Kinetic Enolates
Thermodynamic Enolates:
• The Thermodynamic enolate predominates under
conditions of thermodynamic control.
• A deprotonation–protonation equilibrium allows
interconversion among the possible enolates.
• Thermodynamic enolates are more highly
substituted enolate and more stable one.

10. Thermodynamic and Kinetic Enolates
Kinetic Enolates:
• The Kinetic Enolate is that which is formed
fastest.
• It is usually formed by removal of the least
sterically hindered α hydrogen.
• Kinetic enolates formed with sterically hindered
base in an aprotic solvent.
• Such as LDA in tetrahydrofuran (THF) or
dimethoxyethane (DME)

11. Example of Thermodynamic and Kinetic Enolates

12. Lithium Enolates
• It is a special type of Kinetic Enolate, means
reaction occur at low temperature and fast.
• It always give less substituted Enolates.
• An strong base for converting carbonyl
compounds to enolates is lithium
diisopropylamide (LDA) or LiN(i-Pr)2.

13. Silyl Enolates
• Silicon is less electropositive than lithium.
• The silyl enol ethers are more stable, and less reactive,
than lithium enolates.
• They are made by treating an enolate or α carbonyl with
a silicon electrophile in presence of base.
• Silyl enol ethers also made from lithium enolates by
treating Lithum enolate with trimethylsilyl chloride.

14. Aza-Enolate
• The enamines are the nitrogen analogues of enols.
• Aza-enolates are the nitrogen analogues of
enolates.
• They are made by deprotonating enamines with
strong base.

15. Reaction of Enolates
• Acid and base catalyzed halogenation.
• Haloform reaction
• Malonic easter synthesis
• Alkylation and halogenation via Lithium and
Silyl enolates.

16. Acid and base catalyzed halogenation
• Carbonyl compounds bearing an α hydrogen can
undergo halogen substitution at the α carbon in
the presence of acid or base.

17. Acid and base catalyzed halogenation
• Carbonyl compounds bearing an α hydrogen can undergo
halogen substitution at the a carbon in the presence of acid.

18. Haloform Reaction
• Methyl ketones react with halogens in the presence of
excess base.
• Multiple halogenations always occur at the carbon of the
methyl group.
• Multiple halogenations occur because addition of the first
halogen makes the remaining α hydrogens more acidic.

20. The Malonic Ester Synthesis
(Alkylation of Ester)
• A useful counterpart of the acetoacetic ester synthesis.
• That allows the synthesis of mono- and disubstituted acetic acid is
called the malonic ester synthesis.

21. The Malonic Ester Synthesis
(Alkylation of Ester)

22. Halogenation via Silyl enolates.
• Electrophilic attack occurs at the α carbon atom.
• The halide ion released in this step.
• Then attacks the silicon atom to release the product and a
molecule of Me3SiX.

23. Alkylation via Lithium Enolates.
• The formation of lithium enolates using lithium
diisopropylamide a useful way to alkylating
ketones in a regioselective way.

24. References
• Organic Chemistry, T.W. Graham Solomons, Craig
B. Fryhle and Scott A. Snyder 11th Edition.
• Organic Chemistry 2nd Edition. Jonathan Clayden
Nick Greeves Stuart Warren