IUPAC numerical multiplier

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 is the opposite order to that which the number is written in Hindu-Arabic numerals: units, then tens, then hundreds, then thousands. For example::548 → octa- (8) + tetraconta- (40) + pentacta- (500) = "octatetracontapentacta-":9267 → 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 → hen- (1) + tetraconta- (40) + dicta- (200) = "hentetracontadicta-":411 → 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-".


"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, "khīlioi" = 1000, "diskhīlioi" = 2000, "triskhīlioi" = 3000, etc, and 13 to 19 are "treiskaideka" etc with the Greek for "and" inserted (as in triskaidekaphobia).


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