Untitled - Kelly Walsh High School

Organic, Biochemistry, and Polymers 309
Quick Tip
Answer: 5-ethyl-2,2-dimethylnonane
Solution:
First, pick the longest chain. This is bold-faced in this example. Since only single
bonds are present between the carbon atoms, this is an alkane. Since the
longest chain has 9 carbons, this is a nonane.
CH 3
CH 3 C CH 2 CH 2 CH CH 2 CH 3
CH 3
CH 2
CH 2 CH 2 CH 3
In the structure above, we could have chosen either of the other two CH 3
groups to be the first carbon on the left-hand side.
Next, number the longest chain from one end to the other with the lowest
number(s) going to the branches. For the above example the numbering of
the chain (boldface carbon atoms) would be:
1 2 3 4 5
6
7 8 9
Once you have assigned these numbers, do not alter them later.
All carbon atoms that are not part of the nine atom main chain are branches.
Branches have -yl endings. It may help you to circle the carbon atoms belonging
in the branches. In the above example, there are three branches. Two consist
of only one carbon and are methyl groups. The remaining branch has two
carbons, so it is an ethyl group. We arrange the branches alphabetically. If there
is more than one of a particular type use a prefix (such as di-, tri-,and tetra-.).
The two methyl groups are designated dimethyl. We indicate the position of
each branch with a number already determined from the main chain. Each
branch must get its own number even if it is identical to one already used.