Aldehydes, Ketones and Carboxylic Acids

Lesson

Part 1 — compounds with the carbonyl group C=O: naming, making and their reactions.

In this lesson you will

Name aldehydes and ketones and explain the structure and polarity of the carbonyl group
Write methods of preparing aldehydes and ketones, including Rosenmund, Stephen, Etard and Friedel–Crafts reactions
Explain nucleophilic addition and the relative reactivity of aldehydes and ketones
Write reduction, oxidation (Tollens’ and Fehling’s tests), aldol, Cannizzaro and haloform reactions

Table of familiar carbonyl compounds and carboxylic acids and where they are met
Compound	Where you meet it
Methanal (formalin)	Preserving biological specimens
Propanone (acetone)	Nail-polish remover, solvent
Benzaldehyde	Bitter-almond flavour
Cinnamaldehyde	Smell of cinnamon (dalchini)
Ethanoic acid	Vinegar

Concept

Naming aldehydes and ketones

Aldehydes: replace -e of the alkane by -al (the CHO carbon is C1). Ketones: replace -e by -one, with a locant. Aromatic examples have common names that are still used.

Table of common and IUPAC names of aldehydes and ketones
Structure	Common name	IUPAC name
$\ce{HCHO}$	Formaldehyde	Methanal
$\ce{CH3CHO}$	Acetaldehyde	Ethanal
$\ce{CH3CH(CH3)CHO}$	Isobutyraldehyde	2-Methylpropanal
$\ce{CH3COCH3}$	Acetone	Propan-2-one (propanone)
$\ce{CH3COCH2CH3}$	Ethyl methyl ketone	Butan-2-one
$\ce{C6H5CHO}$	Benzaldehyde	Benzenecarbaldehyde
$\ce{C6H5COCH3}$	Acetophenone	1-Phenylethan-1-one

Diagram

Structure of the carbonyl group

The carbonyl carbon is sp² hybridised: three σ bonds in a plane at about 120°, plus a π bond to oxygen. Oxygen is more electronegative, so the C=O bond is polar: carbon is an electrophile, oxygen a nucleophile/Lewis base.

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