Section 1 of 7How an organic name is built
The stem
- The stem The first part of the name tells you how many carbon atoms are in the longest continuous carbon chain.
The ending
- The ending The second part, the suffix, tells you the functional group,
- which is the atom or group that gives the compound its characteristic reactions.
Families
- Families Compounds with the same functional group belong to one family, called a homologous series, and have similar chemical properties.
Section 2 of 7Stems for the carbon chain
| Number of carbon atoms | Stem |
|---|---|
| 1 | Meth- |
| 2 | Eth- |
| 3 | Prop- |
| 4 | But- |
| 5 | Pent- |
| 6 | Hex- |
Section 3 of 7Endings and functional groups
| Family | Ending | Functional group | Example |
|---|---|---|---|
| Alkane | -ane | None, only C–C single bonds | Methane, CH4 |
| Alkene | -ene | C=C double bond | Ethene, C2H4 |
| Alcohol | -anol | –OH | Propanol, C3H7OH |
| Carboxylic acid | -anoic acid | –COOH | Butanoic acid, C3H7COOH |
| Ester | -yl ...-anoate | –COO– in the middle of the chain | Ethyl ethanoate |
| Amine | -amine | –NH2 | Pentylamine |
Section 4 of 7Naming step by step
1
Find the longest continuous chain of carbon atoms and choose the matching stem.
2
Identify the functional group and choose the correct ending.
3
Join the stem and the ending, for example propane or propene, and propanol for three carbons with an –OH group.
4
If the functional group can sit on more than one carbon, number the chain and put the number before the ending, as in propan-1-ol and propan-2-ol.
5
If two identical functional groups are present, add di- before the ending, as in ethane-1,2-diol.
Section 5 of 7Isomers and numbering
Same formula, different structure
What isomers are
- What isomers are Isomers are compounds with the same molecular formula but different arrangements of atoms.
- Propan-1-ol and propan-2-ol both have the formula C3H8O.
Numbers tell them apart
- Numbers tell them apart The number shows which carbon carries the functional group, so each isomer gets its own name.
- Number from the end that gives the lowest number.
Level required
- Level required You are mainly expected to name straight-chain compounds and unbranched isomers.
- In branched names, the numbers show where side chains are attached, which you should be able to interpret.
Section 6 of 7Key terms
| Term | Meaning |
|---|---|
| Functional group | The atom or group of atoms that gives a family of organic compounds its characteristic chemical properties. |
| Homologous series | A family of compounds with the same functional group and general formula. |
| Stem | The part of the name that shows the number of carbon atoms in the longest chain. |
| Isomers | Compounds with the same molecular formula but different structural formulae. |
| Suffix | The ending of a name that shows the functional group. |
Section 7 of 7Exam technique
1
Choosing the stem by counting carbon atoms in any branch rather than in the longest continuous chain.
2
Forgetting the number in names such as propan-1-ol and propan-2-ol, so that two isomers get the same name.
3
Mixing up the endings-ene is the C=C alkene, but -anol is the alcohol with –OH.
4
Treating esters like single-word names. They have two parts, such as ethyl ethanoate.
5
Assuming isomers have the same structure because their molecular formula matches. Only the formula is shared.