Naming alkanes

carbon number	stem
1	meth
2	eth
3	prop
4	but
5	pent
6	hex
7	hept
8	oct

The name of a branched hydrocarbon can be divided into four parts:
locator + prefix + stem + suffix.

The stem is defined by the number of carbon atoms in the longest chain.

Counting carbon atoms: Consider the five representations of the same molecule shown below. In each case the number of carbon atoms in the longest chain is four. This is easily seen for the two representations at the right-hand end. Roll your mouse over the first three structures to see that it is true for these also.


(CH₃)₂CHCH₂CH₃		CH₃CH₂CH(CH₃)₂

The suffix for saturated hydrocarbons (alkanes) is -ane.

carbon number	name
1	methyl
2	ethyl

The prefix is the name given to the branch. The names of one- and two-carbon branches are given in the table at the right. As can be seen these are the names of the corresponding alkane following by -yl.

The locator gives the number of the carbon in the longest chain that bears the branch. Count from the end of the chain closest to the branch point so that the carbon has the lower of the two possible numbers.

The name of the hydrocarbon shown above is 2-methylbutane.