I recently did an experiment where the addition of bromine to
trans-cinnamic acid gives a dibromide with two stereocenters (chiral
centers). Thus, there were four stereoisomers possible (see figures on
page 136 below).
According to the melting points of my product, I ended up with the
racemic mixture (2R,3S) and (2S,3R), erythro diastereomer (see below).
EVERYTHING I have read points to the idea that this should be an anti
addition, but the teaching assistant has just told me, no, this is a syn
addition since we have ended up with the erythro diastereomer. How can
this be? All the literature says that when a bromonium ion is formed in
the bromination of an alkene, this is anti addition.
Showing a lot of detail, please draw out the mechanism of the reaction
of bromine with trans-cinnamic acid step-by-step for me. How does each
bromine enter?
Is it syn or anti addition or both?
Isn’t the erythro diastereomer a meso compound?
Chemistry Homework Solutions
#11216
bromination of trans-cinnamic acid
I recently did an experiment where the addition of bromine to trans-cinnamic acid gives a dibromide with two stereocenters (chiral centers). Thus, there were four stereoisomers possible (see figures on page 136 on attachment).
According to the melting points of my product, I ended up with the racemic mixture (2R,3S) and (2S,3R), erythro diastereomer (see attachment). EVERYTHING I have read points to the idea that this should be an anti addition, but the teaching assistant has just told me, no, this is a syn addition since we have ended up with the erythro diastereomer. How can this be? All the literature says that when a bromonium ion is formed in the bromination of an alkene, this is anti addition.
(1) Showing a lot of detail, please draw out the mechanism of the reaction of bromine with trans-cinnamic acid step-by-step for me. How does each bromine enter?
(2) Is it syn or anti addition or both?
(3) Isn't the erythro diastereomer a meso compound?
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- stereochemistry of bromine addition to trans-cinnamic acid; syn or anti addition? - This problem is from Modern Projects and Experiments in Organic Chemistry by Mohrig, Hammond, Schatz, and Morrill. (1) Showing a lot of detail, please draw out the mechanism of the reaction step-by ...
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