---
title: "Enols, Enolates and Alpha Substitution"
description: "A carbonyl compound has a second reactive site, the carbon next to the group, which becomes nucleophilic when a proton is removed. That flip from electrophile to nucleophile is what lets carbonyl comp"
canonical: https://lightmysky.com/learn/science/enols-enolates-and-alpha-substitution-mt_EltcLAjnLC
source: https://lightmysky.com/learn/science/enols-enolates-and-alpha-substitution-mt_EltcLAjnLC.md
retrieved: 2026-09-12
---

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# Enols, Enolates and Alpha Substitution

A carbonyl compound has a second reactive site, the carbon next to the group, which becomes nucleophilic when a proton is removed. That flip from electrophile to nucleophile is what lets carbonyl compounds react with each other.

Subject: Science · Area: Chemistry · Ages 20 to 21
Page: https://lightmysky.com/learn/science/enols-enolates-and-alpha-substitution-mt_EltcLAjnLC

## Ready when they can

- Explains alpha acidity from delocalisation of the resulting anion onto oxygen
- Draws keto and enol forms and predicts which dominates for a simple ketone and for a diketone
- Chooses between a base that deprotonates completely and one that sets up a small equilibrium, with the consequence for the product
- Predicts the site of alkylation or halogenation for an unsymmetrical ketone

## Lesson: The carbon next door fights back

A carbonyl compound has a second reactive site, the alpha carbon next to the group. Its hydrogens are far more acidic than ordinary C-H bonds because the resulting anion shares its charge onto oxygen through delocalisation. Pull one off with base and you hold an enolate, an anion with its charge spread over carbon and oxygen.

**Example.** A ketone in a bottle is always shifting a little into its enol form, with the alpha hydrogen moved to oxygen and a double bond beside it. For a simple ketone the keto form wins by a huge margin. A diketone with a second carbonyl to share the load holds far more enol.

The choice of base matters enormously. A strong hindered base drives deprotonation to completion, banking the full enolate. A weaker base sets up only a small equilibrium concentration, and each choice leads to different products.

**Tip.** An unsymmetrical ketone offers two different alpha positions. A bulky base grabs the more exposed hydrogen, while a small base with time to equilibrate favours the more substituted enolate. Match the base to the site you want.

**Recap.** Delocalisation makes the alpha proton acidic, and the base you pick decides how much enolate you hold and where.

## Practice

8 questions on this page, each with its working shown.

## Needs first

- [Nucleophilic Acyl Substitution and the Reactivity Ladder](https://lightmysky.com/learn/science/nucleophilic-acyl-substitution-and-the-reactivity-ladder-mt_b60fq2aQ7r)
- [pKa as a Predictive Tool in Organic Chemistry](https://lightmysky.com/learn/science/pka-as-a-predictive-tool-in-organic-chemistry-mt_fI03mNIC_m)

## Opens up

- [Organocatalysis: Enamine and Iminium Activation](https://lightmysky.com/learn/science/organocatalysis-enamine-and-iminium-activation-mt_E3lmwAFuIO)
- [Aldol and Claisen: Building Carbon Skeletons](https://lightmysky.com/learn/science/aldol-and-claisen-building-carbon-skeletons-mt_LYpEw4EpOX)