IUPAC numerical multiplier

The numerical multiplier (or multiplying affix) in IUPAC nomenclature indicates how many particular atoms or functional groups are attached at a particular point in a molecule. The affixes are derived from both Latin and Greek.

Compound affixes

The affix for a number larger than twelve is constructed in the opposite order to that which the number is written in Hindu-Arabic numerals: units, then tens, then hundreds, then thousands. For example:

548 â†' octa- (8) + tetraconta- (40) + pentacta- (500) = octatetracontapentacta-

9267 â†' hepta- (7) + hexaconta- (60) + dicta- (200) + nonalia- (9000) = heptahexacontadictanonalia-

The numeral one

While the use of the affix mono- is rarely necessary in organic chemistry, it is often essential in inorganic chemistry to avoid ambiguity: carbon oxide could refer to either carbon monoxide or carbon dioxide. In forming compound affixes, the numeral one is represented by the term hen- except when it forms part of the number eleven (undeca-): hence

241 â†' hen- (1) + tetraconta- (40) + dicta- (200) = hentetracontadicta-

411 â†' undeca- (11) + tetracta- (400) = undecatetracta-

The numeral two

In compound affixes, the numeral two is represented by do- except when it forms part of the numbers 20 (icosa-), 200 (dicta-) or 2000 (dilia-).

Icosa- v. eicosa-

IUPAC prefers the spelling icosa- for the affix corresponding to the number twenty on the grounds of etymology. However both the Chemical Abstracts Service and the Beilstein database use the alternative spelling eicosa-.

Etymology

"mono-" is from Greek monos = "alone". "un" = 1 and "nona-" = 9 are from Latin. The others are derived from Greek numbers.

Linguists should note that the forms 100 and upwards are not correct Greek. In Ancient Greek, hekaton = 100, diakosioi = 200, triakosioi = 300, etc. The numbers 200-900 would be confused easily with 22 to 29 if they were used in chemistry. khīlioi = 1000, diskhīlioi = 2000, triskhīlioi = 3000, etc., and 13 to 19 are treiskaideka etc. with the Greek for "and" inserted (as in triskaidekaphobia).

Notes and references

• Panico, R.; & Powell, W. H. (Eds.) (1994). A Guide to IUPAC Nomenclature of Organic Compounds 1993. Oxford: Blackwell Science. ISBN 0-632-03488-2.