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 I don’t understand why the erythro diastereomer appears
to have been formed by syn addition. I can not seem to work this problem
out using my molecular models.
Showing a lot of detail, please draw out the mechanism of the reaction
step-by-step for me.
Is it syn or anti addition or both?
Isn’t the erythro diastereomer a meso compound?
If my melting points came out about 5 degrees Celsius under the mp of
202-204 recorded below, is it because there was some threo diastereomer
in my product?
Chemistry Homework Solutions
#11160
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-step for me.
(2) Is it syn or anti addition or both?
(3) Isn't the erythro diastereomer a meso compound?
(4) If my melting points came out about 5 degrees Celsius under the mp of 202-204 recorded below, is it because there was some threo diastereomer in my product?
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