Organic Chemistry I: Alkanes: Nomenclature

Although many different types of nomenclature, or naming systems, were employed in the past, today only the International Union of Pure and Applied Chemistry (IUPAC) nomenclature is acceptable for all scientific publications. In this system, a series of rules has been created that is adaptable to all classes of organic compounds. For alkanes, the following rules apply.

Identify the longest continuous chain of carbon atoms. The parent name of the alkane is the IUPAC-assigned name for the alkane of this number of carbon atoms (see Table 1 ). Thus, if the longest chain of carbon atoms has six carbon atoms in it, the parent name for the compound is hexane.

TABLE 1

Iupac Names of the First Twenty Parent Alkanes

Number of carbon atoms	Name
1	methane
2	ethane
3	propane
4	butane
5	pentane
6	hexane
7	heptane
8	octane
9	nonane
10	decane
11	undecane
12	dodecane
13	tridecane
14	tetradecane
15	pentadecane
16	hexadecane
17	heptadecane
18	octadecane
19	nonadecane
20	icosane

Identify the substituent groups attached to the parent chain. A substituent group is any atom or group that has replaced a hydrogen atom on the parent chain.

Number the continuous chain in the direction that places the substituents on the lowest-numbered carbon atoms.

Write the name of the compound. The parent name is the last part of the name. The name(s) of the substituent group(s) and the location number(s) precede the parent name. A hyphen separates the number associated with the substituent from its name. If two substituents are on the same carbon of the parent chain, the number of the carbon they are attached to is written before each substituent name. If the two substituents are identical, the numbers are both written before the substituent name, and the prefix “di” is added to the name. Substituent group names are placed in alphabetical order.