Learn English – Why “meth-“, “eth-“, “prop-“, when there is “uni-“,”di-“,”tri-“


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?

Best Answer

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).