Difference Between Enols Enolates and Enamines

Key Difference – Enols vs Enolates vs Enamines
 

Enols, enolates and enamines are three different types of organic compounds. Enols are also known as alkenols. That is because an enol is formed by combining an alkene group with an alcohol group. It is a reactive structure because enols occur as intermediate compounds in chemical reactions. Enolates are derived from enols. An enolate is the conjugated base of an enol. This means an enolate is formed by the removal of a hydrogen atom from the hydroxyl group of an enol. Enamines are amine compounds which contain an amine group adjacent to a double bond. The chemical reactivity of enolates and enamines are nearly similar. The key difference between enols, enolates and enamines is that enols contain a hydroxyl group with an adjacent C=C double bond and enolates contain a negative charge on the oxygen atom of an enol whereas enamines contain an amine group adjacent to a C=C double bond.

CONTENTS

1. Overview and Key Difference
2. What are Enols
3. What are Enolates
4. What are Enamines
5. Side by Side Comparison – Enols vs Enolates vs Enamines in Tabular Form
6. Summary

What are Enols?

Enols are organic compounds that contain a hydroxyl group adjacent to an alkene group (C=C double bond). An enol is formed by the combination of an alcohol with an alkene. The name of this compound is derived from the starting compound of its formation; “en” from an alkene and “ol” from alcohol.

When compared with enolates and enamines of similar molar mass, enols have the least nucleophilic reactivity. This means the enols are poorly nucleophilic. However, its nucleophilicity is governed by the electron-rich pi bond, which comprises of an additional electron density from oxygen atom of the hydroxyl group.

Enols are often obtained by the removal of a hydrogen atom from the alpha carbon of a carbonyl compound. Alpha carbon is the carbon atom that is adjacent to the carbonyl group. This is a deprotonating reaction since it includes a proton removal. If this proton does not return, it results in an enolate ion.

What are Enolates?

Enolates are the conjugated bases of enols. Therefore, an enolate is formed by the removal of a hydrogen atom from the hydroxyl group of an enol. The enolate is the anionic form of the enol. Enolate has a negative charge on the oxygen atom that is located adjacent to a C=C double bond. Enolates can be formed from enols using a base. The hydrogen atom of the hydroxyl group of the enol can be removed and reacted with the base, resulting in the enolate. An enolate can be obtained when an aldehyde or a ketone react with a suitable base.

Enolates effective react with electrophiles due to its high nucleophilicity. The nucleophilic reactivity of enolates is higher than the enols and enamines. The nucleophilicity of enolate anion occurs due to several reasons.

• The oxygen atom has a small atomic radius
• The enolate has a formal negative charge
• When enolate and enamine is compared the oxygen in enolate is highly electronegative than nitrogen atom in the enamine

What are Enamines?

Enamines are organic compounds composed of an amine group adjacent to a C=C double bond. An enamine is formed by the condensation of an aldehyde or ketone with a secondary amine. Enamines are considered as nitrogen analogs of enols.

Enamines reacts in a similar way to that of enolate anions. When compared with enols and enolates, the nucleophilic reactivity of enamines is moderate to that of enols and enolates. This moderate nucleophilicity of enamines results due to the low electronegativity of nitrogen atom compared to the oxygen atom in enols and enolates. However, the reactivity of enamines is different from each other based on the alkyl group attached to the molecule.

What is the Difference Between Enols and Enolates and Enamines?

Enols vs Enolates vs Enamines
Enols	Enols are organic compounds that contain a hydroxyl group adjacent to an alkene group (C=C double bond).
Enolates	Enolates are the conjugated bases of enols.
Enamines	Enamines are organic compounds composed of an amine group adjacent to a C=C double bond.
Functional groups adjacent to the C=C bond
Enols	Enols contain a hydroxyl group.
Enolates	Enolates contain a negatively charged oxygen atom.
Enamines	Enamines contain an amine group.
Presence of Nitrogen
Enols	Enols do not contain nitrogen.
Enolates	Enolates do not contain nitrogen.
Enamines	Enamines contain nitrogen.
Nucleophilic Reactivity
Enols	Enols are less reactive than enolates and enamines.
Enolates	Enolates are reactive than enols and enamines.
Enamines	Enamines are moderately reactive.
Preparation
Enols	Enols are formed by the removal of a hydrogen atom from the alpha carbon of a carbonyl compound.
Enolates	Enolates are formed from enols using a base; the base can react with the hydrogen atom of the hydroxyl group of Enol.
Enamines	Enamines are formed by the condensation of an aldehyde or ketone with a secondary amine.

Summary – Enols vs Enolates vs Enamines

Enols and enolates are closely related because enolates are formed from enols. Enamines contain amine groups adjacent to an alkene group. The difference between enols, enolates and enamines is that enols contain a hydroxyl group with an adjacent C=C double bond and enolates contain a negative charge on the oxygen atom of an enol whereas enamines contain an amine group adjacent to a C=C double bond.

Reference:

1.Hunt, Ian R. Ch18: Enols, Enolates and Tautomerism. Available here 
2.“Enamine.” Wikipedia, Wikimedia Foundation, 18 Mar. 2018. Available here  
3.“Enol.” Wikipedia, Wikimedia Foundation, 28 Feb. 2018. Available here

Image Courtesy:

1.’Dimedon Enol’By NEUROtiker – Own work, (Public Domain) via Commons Wikimedia
2.’Enolate aldol formation mechanism’By Walkerma – Own work, (Public Domain) via Commons Wikimedia  
3.’Enamine-2D-skeletal’ (Public Domain) via Commons Wikimedia