synthesisproblems

synthesisproblems - CH 310M/318M Dr Brian M Bocknack...

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CH 310M/318M Dr. Brian M. Bocknack Synthesis Problems in Organic Chemistry In a synthesis problem , you need to propose a sequence of reactions to prepare some target compound from a particular starting material (or starting materials). Consider the following synthesis problem as a representative example. Problem : Propose a sequence of reactions to prepare cis-2-hexene from 1-pentyne and any alkyl halide necessary. You may also use any other organic and/or inorganic reagents necessary during the course of your synthesis. The most effective strategy to take when confronted with a synthesis problem is to. .. “THINK BACKWARDS” As you progress in your study of organic chemistry, you will learn a large number of reactions. Any one of these reactions could end up being the key step in the synthesis you propose! To narrow down the number of reactions that you have to consider, you want to begin by thinking about how the target could be formed from a suitable precurser, in a single reaction. There may be several possible precursors! Next, consider how these immediate precursors to the target could be formed in a single step. Keep working “backwards” in this way, until the precursors are the “allowed” starting materials defined in the problem. This approach to working synthesis problems is called retrosynthetic analysis . Before we consider the retrosynthetic analysis for our sample problem, let’s consider the three types of chemical operations that are typically involved in an organic synthesis. s Functional group transformations Most of the reactions you have learned at this (early) stage in your study of organic chemistry involve a functional group transformation – one functional group is converted into another C C CH 3 CH 2 CH 2 H R X C C H CH 3 CH 2 CH 2 CH 3 H 1-pentyne alkyl halide cis -2-hexene “target” starting materials from and
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during the course of the reaction. For example, in the hydrohalogenation of an alkene
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This note was uploaded on 07/16/2008 for the course CH 310M taught by Professor Iverson during the Spring '05 term at University of Texas.

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synthesisproblems - CH 310M/318M Dr Brian M Bocknack...

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