---
title: "Aldol and Claisen: Building Carbon Skeletons"
description: "Once one carbonyl compound can be made nucleophilic, it attacks another, and a new carbon to carbon bond appears. Which product forms depends on whether the electrophile can lose a group after the att"
canonical: https://lightmysky.com/learn/science/aldol-and-claisen-building-carbon-skeletons-mt_LYpEw4EpOX
source: https://lightmysky.com/learn/science/aldol-and-claisen-building-carbon-skeletons-mt_LYpEw4EpOX.md
retrieved: 2026-09-12
---

> **Agent view.** This is the Markdown twin of the page, for tools and assistants.
> When to use this site, and the call that answers each job: https://lightmysky.com/agent-instructions.md
> API description (OpenAPI 3.1): https://lightmysky.com/openapi.json · Authentication: https://lightmysky.com/auth.md
> Pricing: https://lightmysky.com/pricing.md · Catalog: https://lightmysky.com/llms.txt · Full catalog: https://lightmysky.com/llms-full.txt
> Every machine-readable file on this domain: https://lightmysky.com/.well-known/ai-catalog.json
> Ask for Markdown with `Accept: text/markdown`, a `.md` address, or `?mode=agent`.

# Aldol and Claisen: Building Carbon Skeletons

Once one carbonyl compound can be made nucleophilic, it attacks another, and a new carbon to carbon bond appears. Which product forms depends on whether the electrophile can lose a group after the attack.

Subject: Science · Area: Chemistry · Ages 20 to 21
Page: https://lightmysky.com/learn/science/aldol-and-claisen-building-carbon-skeletons-mt_LYpEw4EpOX

## Ready when they can

- Draws an aldol addition and the dehydration that follows it, with arrows throughout
- Draws a Claisen condensation and explains why an ester gives a different outcome from a ketone
- Predicts the products of a crossed reaction and states the conditions that make it useful rather than a mixture
- Works backwards from an enone to the two carbonyl compounds that formed it

## Lesson: Joining carbons with carbonyls

The aldol addition joins an enolate to an aldehyde or ketone. The product is a beta-hydroxy carbonyl, two functional groups separated by one carbon. Gentle heating then removes water to give a conjugated enone. Addition plus dehydration is called the condensation.

**Example.** The Claisen condensation is the ester counterpart. An ester enolate attacks another ester, and alkoxide leaves, giving a beta-keto ester. That leaving group is exactly why esters give a different outcome from ketones. Ketones have no group able to leave, so they stop at the addition product.

Mixing two different carbonyl partners can give four products, so crossed reactions need planning. The trick is to make only one partner able to form an enolate, or only one able to accept it. An aldehyde with no alpha hydrogens makes a clean acceptor.

**Tip.** Read an enone backwards to find its makers. Cut beside the double bond: the carbonyl side came from the acceptor, and the alpha side came from the enolate donor. Then ask what had to be controlled to avoid a mixture.

**Recap.** Enolate plus carbonyl builds the skeleton, the leaving group decides the family, and planning tames the cross.

## Practice

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

## Needs first

- [Enols, Enolates and Alpha Substitution](https://lightmysky.com/learn/science/enols-enolates-and-alpha-substitution-mt_EltcLAjnLC)

## Opens up

- [Organometallic Nucleophiles: Grignard and Organolithium Reagents](https://lightmysky.com/learn/science/organometallic-nucleophiles-grignard-and-organolithium-reagents-mt_0X06qlyafO)