# Functional group

A functional group is a small group of atoms in an organic molecule that decides how it reacts. Molecules with the same group react in similar ways, whatever the rest of the molecule looks like.

Chemistry (university) · Part 09: Organic structure and stereochemistry · Card 1 of 9 · Last updated 2026-10-19

## Analogy

Like the handle on a tool: a screwdriver or a hammer may differ, but the handle tells you how to hold it.

## Example

**Common groups**

C=C: alkene     C≡C: alkyne
R–OH: alcohol     R–O–R: ether
R–C(=O)–R: ketone     R–CHO: aldehyde
R–COOH: acid     R–NH₂: amine

## In practice

The OH group makes ethanol an alcohol, and the COOH group makes acetic acid an acid.

## Practice

### Flashcards

- **What is a functional group?** A group of atoms that decides how an organic molecule reacts.

## Questions people ask

### How do I find the functional group in a molecule?

Look for atoms other than carbon and hydrogen, and for double or triple bonds. An O attached to H is an alcohol. A C=O with two carbons attached is a ketone. A C=O with an OH attached is a carboxylic acid. Use a table to match each pattern.

### Why does the functional group matter more than the carbon chain?

The carbon chain is mostly unreactive C–C and C–H bonds. The functional group has polar bonds, lone pairs or pi bonds that attract other reagents. So most reactions happen at the functional group, and the rest of the molecule only changes the details.

## Related concepts

- [IUPAC naming of alkanes](https://studyvisually.com/learn/science/chemistry-university/chemistry-university-part-9/chemistry-university-part-9-concept-2)

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