Introduction to Nomenclature
where ”C” and ”H” are used to represent the number of carbon and hydrogen atoms present
in one molecule. If C = 2, then H = 6.
Many textbooks put this in the following format:
CnH2n+2where ”Cn” and ”H2n+2” represent the number of carbon and hydrogen atoms present in one
molecule. If Cn= 3, then H2n+2= 2(3) + 2 = 8. (For this formula look to the ”n” for the
number, the ”C” and the ”H” letters themselves do not change.)
Progressively longer hydrocarbon chains can be made and are named systematically, de-
pending on the number of carbons in the longest chain.
18.2 Naming carbon chains up to twelve.
- methane (1 carbon)
- ethane (2 carbons)
- propane (3 carbons)
- butane (4 carbons)
- pentane (5 carbons)
- hexane (6 carbons)
- heptane (7 carbons)
- octane (8 carbons)
- nonane (9 carbons)
- decane (10 carbons)
- undecane (11 carbons)
- dodecane (12 carbons)
The prefixes of the first three are the contribution of a German Chemist, August Wilhelm
Hoffman, who also suggested the name quartane for 4 carbons in 1866. However, the but-
prefix had already been in use since the 1820s and the name quartane never caught on.
He also recommended the endings to use the vowels, a, e, i (or y), o, and u, or -ane, -
ene, -ine or -yne, -one, and -une. Again, only the first three caught on for single, double,
and triple bonds and -one was already in use for ketones. Pent, hex, hept, oct, and dec
all come from the ancient Greek numbers (penta, hex, hepta, octa, deka) and oddly, non,
from the Latin novem. For longer-chained alkanes we use the special IUPAC multiplying
affixes. For example, pentadecane signifies an alkane with 5+10 = 15 carbon atoms. For
chains of length 30, 40, 50, and so on the basic prefix is added to -contane. For example,
C 57 H 116 is named as heptapentacontane. When the chain contains 20-29 atoms we have
an exception. C 20 H 42 is known as icosane, and then we have, e.g. tetracosane (eliding the
”i” when necessary). For the length 100 we have ”hecta” but for 200, 300 ... 900 we have
”dicta”, ”tricta”, and so on, eliding the ”i” on ”icta” when necessary; for 1000 we have ”kilia”
but for 2000 and so on, ”dilia”, ”trilia”, and so on, eliding the ”i” on ”ilia” when necessary.
We then put all of the prefixes together in reverse order. The alkane with 9236 carbon
atoms is then hexatridinoniliane.