2. A student's isolated "product" had a melting point of 130-133°C. The IR matched that of cinnamic acid. One likely exp
Posted: Thu Dec 02, 2021 6:50 am
Which mechanism is supported by the observed melting point of your product? Draw two curly-arrow mechanisms from cinnamaldehyde, one to each stereoisomer of your product. You may do this neatly by hand.
H COOH H + Br-Br Br 1 2 COOH 3 Br glacial acetic acid trans-cinnamic acid 2,3-dibromo-3-phenylpropanoic acid Carefully examine 2,3-dibromo-3-phenylpropanoic acid and identify the asymmetric centers (also called chiral centers or chirality centers). You will see that carbons 2 & 3 are asymmetric centers, and therefore 2,3-dibromo-3- phenylpropanoic acid has four stereoisomers indicated below. Br Br COOH Br COOH Br COOH Br COOH Br Br Br (2R, 3R) (28, 35) (2R, 38) (2S, 3R) To help you visualize the stereochemical relationships, here are the Fischer projections of the above compounds. COOH COOH COOH COOH Br Н. H Br Br -H H -Br Н. -Br Br -H Br -Н H Br Ph (2R, 3R) Ph (2S, 3S) Ph (2R, 35) Ph (2S, 3R) Enantiomers of threo-2,3-dibromo-3-phenylpropanoic acid (literature melting point = 91-92 °C) Enantiomers of erythro-2,3-dibromo3-phenylpropanoic acid (literature melting point = 202-204 °C)