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Difference Between Enols Enolates and Enamines

March 22, 2018 Posted by Madhu

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.

Difference Between Enols Enolates and Enamines

Figure 01: The structure of Dimedone; the enol form of Dimedone

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.

Difference Between Enols Enolates and Enamines_Figure 02

Figure 02: Enolate Reactions

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.

Key Difference Between Enols Enolates and Enamines

Figure 03: Structure of an Enamine

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.“Enamine.” Wikipedia, Wikimedia Foundation, 18 Mar. 2018. Available here  
2.“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 

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Filed Under: Organic Chemistry Tagged With: alkenols, Compare Enols Enolates and Enamines, Enamines, Enamines Bonding, Enamines Definition, Enamines Nitrogen, Enamines Preparation, Enolates, Enolates Bonding, Enolates Definition, Enolates Nitrogen, Enolates Preparation, Enols, Enols Bonding, Enols Definition, Enols Enolates and Enamines Differences, Enols Enolates and Enamines Similarities, Enols Nitrogen, Enols Preparation, Enols vs Enolates vs Enamines

About the Author: Madhu

Madhu is a graduate in Biological Sciences with BSc (Honours) Degree and currently persuing a Masters Degree in Industrial and Environmental Chemistry. With a mind rooted firmly to basic principals of chemistry and passion for ever evolving field of industrial chemistry, she is keenly interested to be a true companion for those who seek knowledge in the subject of chemistry.

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