Question 26.2: Naming an Alkane Hydrocarbon Give an appropriate IUPAC name ...
Naming an Alkane Hydrocarbon
Give an appropriate IUPAC name for the following compound, an important constituent of gasoline.
\begin{array}{r c} \begin{matrix} \ \ \ \ \ \ \ \ \ \ \underset{|}{CH_3} \ \ \ \ \ \ \ \ \ \ \ \ \ \underset{|}{CH_3} \ \ \ \ \ \ \ \ \ \ \ \ \ \ \\ \underset{1}{C} H_3-\underset{|2}C-\underset{3}{C}H_2-\underset{4}{C}H-\underset{5}{C}H_3\\ {CH_3}\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \end{matrix} \end{array}
Analyze
We apply the rules listed above. With practice, you will be able to apply the rules without referring back to the list.
The C atoms are numbered in red, and the side-chain substituents to be named are shown in blue. The longest chain of C atoms is five, and the carbons are numbered so that the one with two substituent groups is number 2 instead of number 4. Each substituent is a methyl group, —CH_3. Two methyl groups are on the second C atom, and one methyl group is on the fourth C atom. The correct name is 2,2,4-trimethylpentane.
Assess
If we had numbered the C atoms from right to left, we would have obtained the name 2,4,4-trimethylpentane. This is not an acceptable name because it does not use the smallest numbers possible.