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Unformatted text preview: ISOMERS How are the R and S designations determined?
A. A. Assign priorities to the substituents about a chirality center. B. With the lowest priority furthest from the viewer, draw a circle from the highest (1) to lowest priority (3). (3). R = clockwise (right) O S = counter clockwise (left) O H H
OH O HO O diastereomers = stereoisomers that are not mirror images. enantiomers = mirror images that are not identical
31 32 The R isomer of limonene is found in oranges and the S isomer is found in lemons. Which structure below is the predominant compound found in lemons? How many possible stereoisomers are there for the following compound?
Pr Pr Et Me Et * * * Et A B Me A. 2 B. 4 C. 6 D. 8 E. 12 Pr Me Et Me Pr Et Pr Et Me Pr Et Me Et Et Pr Me Pr Me
33 2n stereoisomers for n stereogenic centers. (R,R,R) (R,R,S) (R,S,R) (R,S,S) (S.R,R) (S,R,S) (S,S,R) (S,S,S)
34 How many stereoisomers of androsterone are there?
A. 8 B. 32 C. 64 D. 128 E. 256 How many stereocenters? How many chair-like rings in this molecule? Tetrodotoxin HO * ** * H* * H* H O androsterone a steroid 27 = 128 = total possible stereoisomers for the above structure.
35 36 1 Tetrodotoxin
How many stereocenters?
a) b) c) d) e) f) g) h) 4 5 6 7 8 9 10 11 Tetrodotoxin
a) b) c) d) e) f) g) h) 4 5 6 7 8 9 10 11 37 38 Tetrodotoxin
How many chair-like rings in this molecule?
a) b) c) d) e) f) g) h) 4 5 6 7 8 9 10 11 Molecules with more than one stereocenter. H Cl HH
Each of these hydrogens hydrogens are prochiral prochiral. Substituting any of these hydrogens will produce different stereoisomers. stereoisomers.
40 40 39 Molecules with more than one stereocenter.
A. R B. S OH Br n=2 22 = 4 stereoisomers
OH Br H Cl
R R HO H H Cl
R H OH H Cl
OH Br *
R R H OH
mirror plane HH
mirror plane HO H R S enantiomers diastereomers
Br OH enantiomers
Br H OH
S S HO H HH
S H OH HO H
41 41 OH S R S S H Cl H Cl H Cl (2S,4R)-4-bromo-2-pentanol bromo- 42 2 What is the name of the enantiomer of (2R,3S,4S)-2-bromo-3-chloro-4-fluoropentane? bromo- chloroCH3 So then how are C and D related? Br
CH 3 Br A. B. C. D. E. (2S,3S,4S)-2-bromo-3-chloro-4-fluoropentane bromo- chloro(2R,3R,4S)-2-bromo-3-chloro-4-fluoropentane bromo- chloro(2S,3S,4R)-2-bromo-3-chloro-4-fluoropentane bromo- chloro(2R,3S,4R)-2-bromo-3-chloro-4-fluoropentane bromo- chlorobromo- chloro(2S,3R,4R)-2-bromo-3-chloro-4-fluoropentane Br CH 3 1 C D A. They are diastereomers. B. They are enantiomers. C. They are conformational isomers. D. This still makes my head hurt. 43 44 Give the stereochemical relationship between the following molecules: Give the stereochemical relationship between the following molecules:
H H HO Cl Cl H HO H (2R,4aS,8aS)-Decahydro-2-naphthalenol mp = 47-48 °C (2R,4aS,8aR)-Decahydro-2-naphthalenol mp = 67 °C a) b) c) d) Enantiomers Diastereomers Identical None of the above
46 a) b) c) d) Enantiomers Diastereomers Identical None of the above
47 Diastereomers have different physical properties! REMEMBER: Enantiomers have identical physical properties, EXCEPT…
O O Pasteur’s Discovery of Enantiomers H
(S)-carvone oil of caraway H
(R)-carvone oil of spearmint
Louis Pasteur (1822-1895) Strasbourg University
(picture: Wikipedia) 48 49 3 A model for electromagnetic radiation (light). - A model for plane polarized light. δ OH unpolarized light δ C + 51 52 The Polarimeter
An instrument for measuring the plane rotation of polarized light.
O H2N H OH O H NH2 OH (S)-phenylalanine = -32.7° 32.7° (R)-phenylalanine = +32.7° +32.7° Jean-Baptiste Biot (17741862, Collège de France) discovered this phenomenon in the early 19th century
(picture: Wikipedia) 53 54 End of Monday, Oct. 11 11 Lecture 55 4 ...
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- Fall '08