Common names and IUPAC names of organic compounds

Many organic compounds had names long before there were rules for naming them: acetone, chloroform, glycerol. These common names (also called trivial names) are still used in laboratories, on labels and in many textbooks. A systematic name is built from the structure by the IUPAC rules, so it can be drawn without having been learned: propan-2-one, trichloromethane, propane-1,2,3-triol.

Common names and their systematic names

Each systematic name links to its drawing exercise.

* Here the 2013 IUPAC recommendations prefer the common name: toluene, acetic acid, ethyl acetate, acetaldehyde and acetonitrile are preferred IUPAC names. In every other row the systematic name is the preferred IUPAC name. The exercises use the systematic names that many courses teach, and the worked answer gives the preferred name too; the summary of the naming rules explains why.

iso-, sec-, tert- and neo-

Common names of alkyl groups use these prefixes; the systematic names number the point of attachment. Each formula below shows the carbon that carries the bond to the rest of the molecule on the right.

In alphabetical order, iso- counts as part of the name (isopropyl is filed under i), while sec- and tert- are ignored (tert-butyl is filed under b).

Functional class names

Another kind of name gives the alkyl group and then the class of compound as a separate word: ethyl bromide for bromoethane, isopropyl alcohol for propan-2-ol, diethyl ether for ethoxyethane. These names are easy to read for simple molecules but become awkward for branched chains and for molecules with several functional groups, which is where the systematic names take over.

Which name should you write?

In a naming exercise or an exam, write the systematic name unless the question asks for another one: any reader can turn it back into the structure without having learned it. Learn the most frequent common names as well, because lab manuals, safety data sheets and teachers use them.