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Organic Chemistry I (CH 320M) Synthesis Practice Problems

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Sandra Watson
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University of Texas at Austin

Organic Chemistry I (CH 320M)

How to approach multi-step synthesis:
1) Compare the final product (aka “target”) to the starting compound. What atoms need to added or
removed?
2) What reactions are required to make the final product (target)? This is the organic compound in the
middle.
3) What reaction will link the starting compound to the middle compound?
First, take an atom “inventory”; in this problem, only 2 H atoms have been removed from the starting material
to form the target. But, we don’t have a single reaction that would perform that transformation‐it will require
more than one step. Second: consider what reactions have we studied to make an alkyne?
Since there are no additional Cs to add, we would not make the product from another alkyne. The reaction we
need is the elimination rxn from a dibromide:
This requires 2 molar equivalents (2 eq.) of strong base to eliminate HBr, two times, to form the alkyne.
Now, the problem has been simplified to a single step organic reaction. What reagents are required to make a
dibromide from an alkene? This is an addition rxn, from chap 6:
In this case, we specify the solvent (CH2Cl2) to ensure that the dibromide is formed. Note, the use of Br2/H2O
would give a bromohydrin and that would not work in this synthesis, since there is no way to eliminate HOBr.
The next page contains a problem set as they would appear in an exam. Try your hand at these.

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Organic Chemistry I (CH 320M)  Synthesis Practice Problems

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