Organic Synthesis Question
In any synthesis questions, we first need to note the number of carbon atoms, is there an increase or decrease in the carbon chain?
In the above question, yes the carbon chain increased from 8 to 9 carbons. This informs us that somewhere in the intermediate steps, a step-up reaction involving nitrile group will be needed.
Then we take a look at the changes in the functional groups. We are starting with alkene and ending with alkene and carboxylic acid group.
To insert a nitrile group, we need to first add halogenoalkane functional group as a precursor. This is a common way to introduce the CN group via nucleophilic substitution in the H2 Chemistry Syllabus.
Next we need to consider how to keep the C=C group in the target molecule. Inevitably, when we add the halogen to the C=C, the alkene functional group will disappear. So how do we reform the C=C after adding the halogen?
There are 3 options,
- Cl-Cl in tetrachloromethane
- Cl-Cl in aq
First option is out as it will convert the functional group to halogenoalkane, which leaves us no way to reform the alkene through elimination.
Second option is also out as both Cl will be substituted by CN group.
Option 3 is our answer as Cl will be added to the the terminal carbon atom and OH will be added to the more substituted carbon atom (Markovnikov Rule) Choosing the correct reagents and condition for the first step is crucial to solving the question as it will set the course of synthesis.
Sequencing the Synthesis Route
After which we can just substitute the terminal Cl with CN and hydrolyse it to COOH. The alkene group can also be reformed via elimination of water.
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