In chemistry, the homologous series for hydrocarbons uses the following prefixes:

  • Meth-
  • Eth-
  • Prop-
  • But-
  • Pent-
  • Hex-
  • Hept-
  • Oct-

Why are these prefixes used, instead of just using "uni-", "di-", "tri-"?

I looked up the prefixes, but there is no dictionary record of them. Still, I think "uni-", "di-", "tri-", were invented first.

Is there a specific reason why, instead of using the normal counting prefixes, new prefixes were used or made up, assuming they were made up for this specific purpose?

  • 6
    Not sure if you care, but the uni-, di-, and tri-, etc, work into the complex molecule nomenclature, to designate how many side groups of a particular type are on a chain. For instance, 18-bromo-12-butyl-11-chloro-4,8-diethyl-5-hydroxy-15-methoxytricos-6,13-dien-19-yne-3,9-dione has two ethyl groups, two double carbon bonds, and two oxygen molecules.
    – Kit Z. Fox
    Jun 3, 2011 at 12:05
  • 3
    This doesn't seem a question specific for English; In Italian, the used prefixes are met-, et-, prop-, but-. It seems more a chemistry question.
    – apaderno
    Jun 3, 2011 at 15:19
  • 4-dimethylaminoazobenzene-4'-sulfonic acid sodium salt (methyl orange).
    – apaderno
    Jun 3, 2011 at 15:21

1 Answer 1


Short answer: they were invented to preserve names of organic substances that already were in use. From Wikipedia's article on number prefixes:

The IUPAC nomenclature of organic chemistry uses the numerical prefixes derived from Greek, except for the prefix for 9 (as mentioned) and the prefixes from 1 to 4 (meth-, eth-, prop-, and but-), which are not derived from words for numbers.

These prefixes were invented by the IUPAC, deriving them from the pre-existing names for several compounds that it was intended to preserve in the new system:

  • methane (via methyl which is in turn from the Greek word for wine),
  • ethane (from ethyl coined by Justus von Liebig in 1834),
  • propane (from propionic which is in turn from pro- and the Greek word for fat), and
  • butane (from butyl which is in turn from butyric which is in turn from the Latin word for butter).
  • 6
    I was surprised since wine (ideally) doesn't contain methyl alcohol. From wikipedia: French chemists Jean-Baptiste Dumas and Eugene Peligot, after determining methanol's chemical structure, introduced "methylene" from the Greek methy = "wine" + hȳlē = "wood" (patch of trees) with the intention of highlighting its origins, "alcohol made from wood (substance)", but with Greek language errors: the Greek for "wood (substance)" is xylo-. The term "methyl" was derived in about 1840 by back-formation from "methylene", and was then applied to describe "methyl alcohol".
    – Neil G
    Jun 3, 2011 at 16:35
  • @NeilG: Why do you say hûlê was not used for the substance wood? As far as I know, it can very well be so used: archimedes.fas.harvard.edu/cgi-bin/… Apr 5, 2013 at 2:18

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