Answer Happy

2. A student's isolated "product" had a melting point of 130-133°C. The IR matched that of cinnamic acid. One likely explanation is that he lost the most volatile reaction component by vaporization. How might the following have affected the loss? 2. Use (or lack of use) of a solid addition (powder) funnel to add solid reagents to the round-bottom flask. b. Use (or lack of use) of stopcock grease. c. Rate of water flow through the condenser, d. Power setting on the heating mantle.

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)