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CH 237 Lab 2 Bromination Of Trans-cinnamic Acid

Sandra Watson
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University of Alabama

Elem Organic Chem Lab (CH 237)

The chemical engineers at The Bond Triplex Company presented the problem for this
experiment to me. They were not sure of the stereochemistry of the intermediates during the
addition reaction that converts trans-cinnamic acid with bromine to make 3-phenylpropanic acid.
Due to the electron-donating effects of some of the substituents on alkenes, the bromine could
potentially be added across the double bond in a syn-addition through a concerted mechanism, in an
anti-addition using an onium ion intermediate, or in a mixture of both additions through a benzylic
carbocation intermediate. The possible products that could form depending on the mechanism that
occurred are erythro-2,3-dibromo-3-phenylpropanoic acid or threo-2,3-dibromo-3-phenylpropanoic
acid. Knowing the stereochemistry of the intermediate dibromides could increase the company’s
efficiency, so they asked for assistance in characterizing the intermediates of the reaction.
The goal of this experiment was to determine if the addition of bromine to trans-cinnamic
acid only adds by syn-addition, only adds by anti-addition, or if both products are produced. To
accomplish this goal, I carried out the bromination of trans-cinnamic acid in order to determine the
stereochemical structure of the dibromide intermediate and find out whether the reaction proceeds
by the usual bromonium ion mechanism or another mechanism.



CH 237 Lab 2 Bromination Of Trans-cinnamic Acid

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