# IUPAC numerical multiplier

Number Multiplier   Number Multiplier
1 mono-   32 dotriaconta-
2 di-   40 tetraconta-
3 tri-   50 pentaconta-
4 tetra-   60 hexaconta-
5 penta-   70 heptaconta-
6 hexa-   80 octaconta-
7 hepta-   90 nonaconta-
8 octa-   100 hecta-
9 nona-   200 dicta-
10 deca-   300 tricta-
11 undeca-   400 tetracta-
12 dodeca-   500 pentacta-
13 trideca-   600 hexacta-
20 icosa-/eicosa-   4000 tetralia-
21 henicosa-/heneicosa-   5000 pentalia-
22 docosa-   6000 hexalia-
23 tricosa-   7000 heptalia-
30 triaconta-   8000 octalia-
31 hentriaconta-   9000 nonalia-

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 → 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-.

## 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.