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Solving Problems: A Chemistry Handbook
Chemistry: Matter and Change
219
SOLVING PROBLEMS:
A CHEMISTRY HANDBOOK
CHAPTER 21
When naming a cyclic alkene, position 1 is assigned to one of the
carbons connected by the double bond, as illustrated here for the
compound 1-ethyl-4-methylcyclohexene.
Naming branched-chain alkenes The parent chain in an alkene
is always the longest chain that contains the double bond, even if
this is not the longest chain of carbon atoms. The numbering of the
parent chain is determined by the position of the double bond. If
there is more than one double bond, the positions of the double
bonds are numbered so as to give the lowest set of numbers. The
following example problem demonstrates how to name a branchedchain alkene.
Example Problem 21-3
Naming Branched-Chain Alkenes
Name the following alkene.
a. The longest continuous carbon chain that includes the two double bonds contains six carbon atoms. The parent name is
hexadiene, where the prefix di- indicates two double bonds.
b. Numbering the chain from right to left gives the lowest numbers (1 and 4) for the double bonds.
CH 3 C CCH 2 C CH 2
CH 3
CH 3 CH 2 CH 3
▲
1-ethyl-4-methylcyclohexene
CH 2 CH 3
6
5
4
3
2
1
CH 3
1-pentene
3-heptene
CH 2 CHCH 2 CH 2 CH 3
CH 3 CH 2 CH 2 CH CHCH 2 CH 3
1
2
3
4
5
6
7
1
2 3 4 5