Every organic name is built from two parts: a stem that counts the carbon atoms and an ending that names the family. Learn four stems and five endings and you can name, and draw, any compound on the IGCSE syllabus.
The stem counts the carbon atoms in the chain: meth- 1, eth- 2, prop- 3, but- 4. The ending names the homologous series: -ane for alkanes, -ene for alkenes, -ol for alcohols and -oic acid for carboxylic acids. A number shows where the functional group sits when it could be in more than one place, as in propan-1-ol or but-2-ene. (Extended) An ester is named alcohol part first (ending -yl) then acid part (ending -oate): ethanol + ethanoic acid gives ethyl ethanoate. (Extended) Structural isomers have the same molecular formula but different structural formulae, such as butane and methylpropane (both C4H10).
Pick a stem and an ending in the simulator and check that your displayed formula matches the name. Count the carbons first, then place the functional group.
| Carbons | Alkane | Alkene | Alcohol | Carboxylic acid |
|---|---|---|---|---|
| 1 | methane CH4 | (none) | methanol CH3OH | methanoic acid HCOOH |
| 2 | ethane C2H6 | ethene CH2=CH2 | ethanol CH3CH2OH | ethanoic acid CH3COOH |
| 3 | propane C3H8 | propene CH3CH=CH2 | propan-1-ol CH3CH2CH2OH | propanoic acid CH3CH2COOH |
| 4 | butane C4H10 | but-1-ene CH2=CHCH2CH3 | butan-1-ol CH3(CH2)3OH | butanoic acid CH3CH2CH2COOH |
In a carboxylic acid the carbon of the −COOH group counts in the stem: ethanoic acid has two carbons, CH3 and COOH. There is no "methene", because a C=C bond needs at least two carbons.
Extended. Esters: name the alcohol part first, then the acid part. Methanol + ethanoic acid → methyl ethanoate, CH3COOCH3; ethanol + propanoic acid → ethyl propanoate, CH3CH2COOCH2CH3.
Four quick checks. Each correct answer earns XP and records this skill on your profile.
What is the name of CH3CH2CH3?
Which compound is butanoic acid?
What is the name of CH3OH?
Which name is correct for CH2=CH2?
Extended. Rearrange the atoms of C4H10 in the simulator. Every arrangement has the same molecular formula, but the atoms are joined differently.
A chain drawn with a bend is the same molecule, not an isomer: follow the bonds, not the shape on the page. Name the longest unbroken carbon chain, so a "bent butane" is still butane. In esters the alcohol gives the first word (ethyl) and the acid gives the second (ethanoate), the reverse of the order in the word equation.
Unlocks once the four checks above are done. Worth more XP, written to IGCSE Paper 2 and Paper 4 standard.
(Extended) Which ester is made from ethanol and ethanoic acid?
(Extended) Which pair are structural isomers?
(Extended) Which compound is an isomer of butane, C4H10?
Which is the structural formula of propan-2-ol?
This skill is now recorded on your profile. Keep the chain going.