Ch. 21 - Enolate Chemistry: Reactions at the Alpha-Carbon See all chapters
All Chapters
Ch. 1 - A Review of General Chemistry
Ch. 2 - Molecular Representations
Ch. 3 - Acids and Bases
Ch. 4 - Alkanes and Cycloalkanes
Ch. 5 - Chirality
Ch. 6 - Thermodynamics and Kinetics
Ch. 7 - Substitution Reactions
Ch. 8 - Elimination Reactions
Ch. 9 - Alkenes and Alkynes
Ch. 10 - Addition Reactions
Ch. 11 - Radical Reactions
Ch. 12 - Alcohols, Ethers, Epoxides and Thiols
Ch. 13 - Alcohols and Carbonyl Compounds
Ch. 14 - Synthetic Techniques
Ch. 15 - Analytical Techniques: IR, NMR, Mass Spect
Ch. 16 - Conjugated Systems
Ch. 17 - Aromaticity
Ch. 18 - Reactions of Aromatics: EAS and Beyond
Ch. 19 - Aldehydes and Ketones: Nucleophilic Addition
Ch. 20 - Carboxylic Acid Derivatives: NAS
Ch. 21 - Enolate Chemistry: Reactions at the Alpha-Carbon
Ch. 22 - Condensation Chemistry
Ch. 23 - Amines
Ch. 24 - Carbohydrates
Ch. 25 - Phenols
Ch. 26 - Amino Acids, Peptides, and Proteins
Johnny Betancourt

Enolates are anions at the the alpha position of carbonyl compounds like ketones and aldehydes. They can participate in many kinds of reactions including tautomerization, alkylation, acylation, condensation, etc. 

Enolate Formation

Enolate formation oxyanion and carbanion resonance structure contributorsEnolate formation, oxyanion and carbanion resonance structure contributorsEnolate anions are intermediates of base-catalyzed tautomerization (aka tautomerism). Carbonyls and enols (aka alkene-ols) are tautomers and exist in equilibrium 

Tautomerization-mechanismTautomerization mechanismReactions:

Alkylation and Acylation

Enolate alkylation and acylationEnolate alkylation and acylation Enolates can undergo alkylation and acylation reactions. In these, the carbanion acts as a nucleophile to attack an electrophile like an alkyl halide or acyl chloride. Acylation reactions form beta-dicarbonyls

Condensation Reactions

Enolates can also attack carbonyls directly through nucleophilic addition, and in this process larger molecules are formed. Condensation reactions like Aldol, Claisen, and Dieckmann

Claisen condensation mechanismClaisen condensation mechanism

Johnny Betancourt

Johnny got his start tutoring Organic in 2006 when he was a Teaching Assistant. He graduated in Chemistry from FIU and finished up his UF Doctor of Pharmacy last year. He now enjoys helping thousands of students crush mechanisms, while moonlighting as a clinical pharmacist on weekends.

Additional Problems
Which one of the following  cannot form an enolate anion? a 2,2-dimethylbutanal b 2-ethylbutanal c 2,3-dimethylbutanal d 3,3-dimethylbutanal e All can form enolate anion
Which of the following compounds exchanges the largest number of hydrogens for deuterium when treated with KOD in D2O? A. 6-methyl-1,4-cycloheptanedione  B. 2-methyl-1,3-cycloheptanedione C. 5-methyl-1,3-cycloheptanedione D. 3-methyl-1,2-cycloheptanedione
Draw cyclohexanone and its enol tautomer. Place the correct symbol between them.
Draw all reasonance forms for the enolate conjugate base that is produced when the compound below is treated with sodium ethoxide. Place the correct symbol between them.
Draw in and circle the most acidic hydrogen (or hydrogens) in each molecule below and place them in order of their acidity with #1 being the most acidic and #4 being the least acidic. 
Which of the following hydrogens is most acidic? Hint: try drawing out the conjugate bases to see which is most stable.
What set of ketone (1) and aldehyde (2) will provide the same alchohol product (3) when submitted to the reaction conditions shown?
Read the following statements and decide whether they are True or False.    1. Enolates are similar to enols but they are for more nucleophilic T or F 2. In order to generate an enolate we we need either an acid or a base to abstract an alpha hydrogen T or F 3. The pka of an alpha hydrogen on a single carbonyl is ~20 T or F 4. The choice of base will determine the extent of enolate formation. T or F
Which base should be used to quantitatively convert this  N,N-dimethylamide into its enolate ion?
Draw the product formed when the following starting material is treated with LDA in THF solution at -78°C. 
Draw the structure(s) of the major organic product(s) of the following reaction.