Question 12.5: Draw all stereoisomers that are possible for the following u...
Draw all stereoisomers that are possible for the following unsaturated alcohol.
Strategy
To show cis-trans isomerism, each carbon of the double bond must have two different groups bonded to it. If a molecule has n double bonds about which cis-trans isomerism is possible, then 2^n isomers are possible, where n is the number of double bonds that show cis-trans isomerism.
Solution
Cis-trans isomerism is possible only about the double bond between carbons 2 and 3 of the chain. It is not possible for the other double bond because carbon 7 has two identical groups on it (review Section 12.2B). Thus, 2^1 =2 stereoisomers (one cis-trans pair) are possible. The trans isomer of this alcohol, named geraniol, is a major component of the oils of rose, citronella, and lemon grass.
