Chemistry - STEREO ISOMERISM Question with Solution | TestHub
For many centuries, the Chinese have used extracts from a group of herbs known as ephedra to treat asthma. A compound named ephedrine has been isolated from these herbs and found to be a potent dilator of air passages in the lungs.
(a) How many stereoisomers does ephedrine have?
(b) The stereoisomer shown here is the one that is pharmacologically active. What is the configuration of each of the asymmetric centers?
ephedrine: 
Options:
Answer:
Solution:
Ans. (A) (a) 4 (b) 1R, 2S.
Sol. (a) Ephedrine, C6H5-CH(OH)-CH(NHCH3)-CH3, has two asymmetric centres and no internal symmetry, so the number of stereoisomers = 22 = 4.
(b) C1: priorities OH CH(NHCH3)CH3 C6H5 H; with H wedged towards the viewer the observed order is counterclockwise, inverted : R. C2: priorities NHCH3 CH(OH)C6H5 CH3 H; H is dashed away and 1 2 3 is counterclockwise : S. The active stereoisomer is (1R, 2S).
