Question 24.6: Writing the IUPAC Name of an Alkene Given the Structural For...
Writing the IUPAC Name of an Alkene Given the Structural Formula
What is the IUPAC name of each of the following alkenes?
a. 
b. 
a. The numbering of the carbon chain is
Because the longest chain containing a double bond has five carbon atoms, this is a pentene. It is a 1-pentene, because the double bond is between carbon atoms 1 and 2. The name of the compound is 3-methyl-1-pentene. Note the placement of hyphens. If the numbering had been in the opposite direction, you would have named the compound as a 4-pentene. But this is unacceptable, because 4 is greater than 1. b. The numbering of the longest chain containing the double bond is
This gives the name 4-butyl-2-nonene. There is a longer chain (of ten carbon atoms), but it does not contain the double bond.