"In earlier times, when relatively few pure organic chemicals were known, new compounds were named at the whim of their discoverer … As the science of organic chemistry slowly grew in the 19th century, so too did the number of known compounds and the need for a systematic method of naming them. … A chemical name typically has four parts in the IUPAC system of nomenclature: prefix, parent, locant, and suffix. The prefix identifies the various substituent groups in the molecule, the parent selects a main part of the molecule and tells how many carbon atoms are in that part, the locants give the positions of the functional groups and substituents, and the suffix identifies the primary functional group. … For historical reasons, some of the simpler branched-chain alkyl groups also have nonsystematic, common names, as noted earlier."