Question 11.7: Naming Alkenes and Alkynes Write the IUPAC name for each of ...
Naming Alkenes and Alkynes
Write the IUPAC name for each of the following:
a. \begin{array}{r c}\begin{matrix} \quad {\underset{|}{{CH_{3}}}} \quad \quad \\ \quad \quad \quad \quad {CH_{3}}-CH-CH=CH-CH_{3} \end{matrix}\end{array} b. CH_{3}-CH_{2}-C\equiv C-CH_{2}-CH_{3}
a.
| Feature | Type | IUPAC Naming | |
| ANALYZE THE PROBLEM |
double bond | alkene | replace the ane of the |
| alkane name with ene |
Step \fbox{1} Name the longest carbon chain that contains the double bond. There are five carbon atoms in the longest carbon chain containing the double bond. Replace the ane in the corresponding alkane name with ene to give pentene.
\begin{array}{r c}\begin{matrix} \quad {\underset{|}{{CH_{3}}}} \quad \quad \\ \quad \quad \quad \quad {CH_{3}}-CH-CH=CH-CH_{3} \end{matrix}\end{array} pentene
Step \fbox{2} Number the carbon chain starting from the end nearer the double bond. Place the number of the first carbon in the double bond in front of the alkene name.
Alkenes or alkynes with two or three carbons do not need numbers. For example, the double bond in ethene or propene must be between carbon 1 and carbon 2.
Step \fbox{3} Give the location and name for each substituent (alphabetical order) as a prefix to the alkene name. The methyl group is located on carbon 4.
b.
| Feature | Type | IUPAC Naming | |
| ANALYZE THE PROBLEM |
triple bond | alkene | replace the ane of the |
| alkane name with yne |
Step \fbox{1} Name the longest carbon chain that contains the double bond. There are six carbon atoms in the longest chain containing the triple bond. Replace the ane in the corresponding alkane name with yne to give hexyne.
CH_{3}-CH_{2}-C\equiv C-CH_{2}-CH_{3} hexyne
Step \fbox{2} Number the carbon chain starting from the end nearer the triple bond. Place the number of the first carbon in the triple bond in front of the alkyne name.
Step \fbox{3} Give the location and name for each substituent (alphabetical order) as a prefix to the alkyne name. There are no substituents in this formula.
Guide to Naming Alkenes and Alkynes
Step \fbox{1}
Name the longest carbon chain that contains the double bond.
Step \fbox{2}
Number the carbon chain starting from the end nearer the triple bond.
Step \fbox{3}
Give the location and name for each substituent (alphabetical order) as a prefix to the alkyne name.