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.
\underset{1}{C}H_{3}—\overset{\begin{matrix} CH_{3} \\ \mid \end{matrix} }{\underset{\begin{matrix} \mid 2 \\ CH_{3} \end{matrix} }{C}}—\underset{3}{C}H_{2}—\overset{\begin{matrix} CH_{3} \\ \mid \end{matrix} }{\underset{4}{C}}H—\underset{5}{C}H_{3}
Analyze
We apply the rules listed above. With practice, you will be able to apply the rules without referring back to the list.
Solve
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.