The main functional groups
| Group | Structure | Name ending (suffix) | Prefix | Example |
|---|---|---|---|---|
| Alkane | C–C, C–H only | -ane | alkyl- | ethane |
| Alkene | C=C | -ene | propene | |
| Alkyne | C≡C | -yne | ethyne | |
| Arene | benzene ring | -benzene | phenyl- | methylbenzene |
| Haloalkane | C–X (X = F, Cl, Br, I) | fluoro-, chloro-, bromo-, iodo- | bromoethane | |
| Alcohol | C–OH | -ol | hydroxy- | ethanol |
| Ether | C–O–C | alkoxy- | methoxyethane | |
| Amine | C–NH₂ | -amine | amino- | ethanamine |
| Aldehyde | –CHO | -al | oxo- | ethanal |
| Ketone | C–CO–C | -one | oxo- | propanone |
| Carboxylic acid | –COOH | -oic acid | carboxy- | ethanoic acid |
| Ester | –COO–C | -oate | methyl ethanoate | |
| Acyl chloride | –COCl | -oyl chloride | ethanoyl chloride | |
| Amide | –CONH₂ | -amide | ethanamide | |
| Nitrile | –C≡N | -nitrile | cyano- | ethanenitrile |
What they look like
Telling similar groups apart
- Aldehyde or ketone? Look at the C=O carbon. If it has an H on it (end of a chain), it's an aldehyde. If it has two carbons, it's a ketone.
- Carboxylic acid or ester? Both have C(=O)O. An acid has O–H; an ester has O–C.
- Ether or alcohol? An alcohol has O–H. An ether's oxygen sits between two carbons.
- Amine or amide? An amide's nitrogen is attached to a C=O. An amine's isn't.
- Primary, secondary, tertiary alcohols depend on how many carbons are attached to the C–OH carbon: one, two or three. This decides how they oxidise.
Spotting them in spectra
IR tells you which groups are present: a broad O–H around 3200–3550 cm⁻¹, a sharp C=O near 1700 cm⁻¹, C≡N near 2250 cm⁻¹. See the IR spectroscopy table.
Quick answers
What is a functional group?
A functional group is an atom or group of atoms in a molecule that gives it its characteristic reactions, such as –OH in alcohols or C=O in ketones.
How many functional groups are there in organic chemistry?
School and first-year courses usually cover about 15: alkanes, alkenes, alkynes, arenes, haloalkanes, alcohols, ethers, amines, aldehydes, ketones, carboxylic acids, esters, acyl chlorides, amides and nitriles.
What is the difference between an aldehyde and a ketone?
Both have C=O. In an aldehyde the C=O carbon is at the end of the chain and has a hydrogen on it. In a ketone the C=O carbon is joined to two other carbons.
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