Beginner Topic 800 of 1102 Organic Chemistry
Aldehydes
Compounds with a terminal carbonyl group, easily oxidized to carboxylic acids.
In-depth explanation of Aldehydes
Aldehydes contain a carbonyl group, C=O, bonded to at least one hydrogen, and the carbonyl sits at the end of the carbon chain. The name ends in -al. Aldehydes are more reactive toward nucleophiles than ketones because the carbonyl carbon carries a larger partial positive charge and has less steric hindrance from alkyl groups. They are easily oxidized to carboxylic acids, which distinguishes them from ketones. Formaldehyde is used in making resins, and it is also a preservative.
Going deeper: Aldehydes
Key ideas: Aldehydes (RCHO) have a carbonyl carbon bonded to at least one H, so they are easily oxidised and more reactive to nucleophiles than ketones. Made by oxidising primary alcohols (PCC), ozonolysis, Rosenmund reduction of acid chlorides (H2, Pd-BaSO4) or DIBAL reduction of esters and nitriles. Tests: Tollens, Fehling (aliphatic only), Schiff reagent. Boiling points are above alkanes but below alcohols.
Common mistakes and connections: Students think benzaldehyde gives a Fehling positive result; it does not. Another error is forgetting that aldehydes lacking alpha hydrogens (HCHO, benzaldehyde) cannot enolise and undergo Cannizzaro instead of aldol. Links to oxidation of alcohols, nucleophilic addition and aldol chemistry.
Visualization of Aldehydes
Formaldehyde is the simplest aldehyde: a planar C=O group with two hydrogens and bond angles near 120 degrees. The interactive lesson shows this as a live animation or chart.
Worked example and use case
Benzaldehyde, C6H5CHO, has the characteristic smell of almonds.
Frequently asked questions about Aldehydes
What is Aldehydes?
Compounds with a terminal carbonyl group, easily oxidized to carboxylic acids.
Is Aldehydes a beginner, intermediate or advanced topic?
Aldehydes is a beginner topic in Organic Chemistry. It needs no earlier chemistry lessons and is a good starting point.
What should I learn before Aldehydes?
Study these earlier topics in Organic Chemistry first: Phenols, Ethers, Williamson Ether Synthesis.
What comes after Aldehydes?
The next topics in Organic Chemistry are Ketones and Nucleophilic Addition to Carbonyls.
Can I practise Aldehydes with quizzes?
Yes. The interactive lesson includes a self-check question on Aldehydes, and the Organic Chemistry quiz draws on every topic in this area.
Where Aldehydes fits in Organic Chemistry
Aldehydes is topic 72 of 148 in Organic Chemistry.