Ephedrine has been known in medicine since the Chinese isolated it from natural sources in about 2800 BC. Its structure has been known since 1885. Ephedrine can be used as a bronchodilator (a compound that enlarges the air passages in the lungs), but it tends to increase blood pressure because it constricts blood vessels. Pseudoephedrine has the same effects, except that it is much less active in elevating blood pressure. Ephedrine is the (1R,2S)-stereoisomer of the structure below (Ph 5 phenyl). Pseudoephedrine is the (1S,2S)-stereoisomer of the same structure.

(a) Draw a line-and-wedge structure for each of these two stereoisomers in which the Ph, CH₃, and the two asymmetric carbons lie in the plane of the page. In this part and part (b), do not draw out the bonds within the —CH₃, —OH, and —NHCH₃ groups explicitly. (More than one correct structure is possible.)

(b) Draw a sawhorse projection and a Newman projection about the C1—C2 bond for each of the structures you drew in part (a). Let the carbon nearest the observer be the one bearing the —OH group.

(c) What is the relationship between these two compounds? Choose from enantiomers, diastereomers, identical molecules, and constitutional isomers. Explain how you know.

(d) Should the melting points of these two compounds be the same or different in principle?

(e) What, if anything, can you say about the optical activities of these two compounds?

Transcribed Image Text:

OH NHCH3 T Ph—CH–CHCH, 2 1