Naming organic compounds
Prefixes for chain length and suffixes for functional groups.
Review these first
Learning objectives
What you need to be able to do
Teacher-mapped phrasing — check against the official Cambridge syllabus for exact wording.
- 11.2.1Name and draw the first four members of the alkanes, alkenes, alcohols and carboxylic acids.
5 minute read
Naming organic compounds
Every IUPAC organic name is built from two parts glued together: a prefix that tells you how many carbon atoms are in the chain, and a suffix that tells you the functional group.
The chain-length prefixes
| Carbons | Prefix |
|---|---|
| 1 | meth- |
| 2 | eth- |
| 3 | prop- |
| 4 | but- |
These are worth memorising cold — they appear in the name of every alkane, alkene, alcohol and carboxylic acid.
The functional-group suffixes
- -ane: alkane (saturated hydrocarbon), e.g. propane, C₃H₈.
- -ene: alkene (contains a C=C double bond), e.g. propene, C₃H₆.
- -ol: alcohol (contains −OH), e.g. propanol, C₃H₇OH.
- -oic acid: carboxylic acid (contains −COOH), e.g. propanoic acid.
Put together: "but" + "ane" = butane (4-carbon alkane); "eth" + "ol" = ethanol (2-carbon alcohol).
Think of it like this
Naming an organic molecule is like naming a hybrid car: the prefix (meth-, eth-, prop-, but-) is the "model" telling you how big the chain is, and the suffix (-ane, -ene, -ol, -oic acid) is the "trim level" telling you which functional group it has.
Worked examples
Method, step by step
Name the alcohol with the structural formula CH₃CH₂CH₂OH.
- 1Count the carbon chain: 3 carbons, so the prefix is prop-.
- 2The −OH functional group gives the suffix -ol.
- 3Combine: propan-1-ol (commonly just "propanol" at this level).
Propanol (propan-1-ol).
Common misconceptions
- Applying the prefix to the wrong count — but- means 4 carbons, not 2; a quick way to check is counting from meth- (1) upward: meth, eth, prop, but.
- Forgetting that the suffix, not the prefix, is what determines the class of compound and hence its reactions — propene and propane share a prefix but react completely differently because of the suffix.
In the exam
- When asked to name a compound from its structure, count the longest continuous carbon chain first to fix the prefix, then identify the functional group for the suffix.
- Carboxylic acid names always end "-oic acid", not just "-oic" — dropping "acid" is a common mark loss.