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Unformatted text preview: 5 - 1 3 The rotation of pure (+)-2-butanol i s + 1 3 . 5 ° o bserved rotation ----r otation of pure enantiomer
= To calculate percentages of ( +) a nd (-) : + 0 .45 ° x 1 00% + 1 3 .5 ° ( -) . = = 3 . 3 % optical purity 3 . 3 % e.e. = e xcess o f (+) over (-) ( +) + ( ) ( +)
(-) - (two equations in two unknowns)
= = 1 00% 3 .3 %
2 = ( +)
= = (+ )
= 1 03 . 3 % - (+) ( 1 00% - (+))
1 00 % = 3 .3% (+) (-)
5-14 5 1 .6% (rounded) 48 .4% D rawing Newman projections is the clearest way to determine symmetry of conformations.
H (b) '' Br ',C I , ( a) ,,-h H Br � CI H
H chiral optically acti ve } Plane includes Br and CI (c) ,,-h H B r � CI CI
H chiral optically acti ve H C I CH2 - C - CI Br H plane of symmetry containing B r-C-C-CI ; not optically active H B r - C - C - Cl HH no asymmetric carbons (e) H I H I I I I I * (d) H Br plane of symmetry-not optically acti ve despite the presence of two asymmetric c �rbons
, , l(:y�20 B , H : H � k�
C2 �CH2 ,,-h H H �CH20 B r H H
H no plane of symmetry optically active (other chair form is equi valent-no pl ane of symmetry) Br H ( f) Br 1 H �
� - - "' H 4 Br plane of symmetry through C - l and C-4-not optically acti ve no asymmetric c arbons Part (2) Predictions of optic al acti v i ty based on asymmetri c centers give the same answers as predictions based on the most symmetric conformation . 85 ...
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This note was uploaded on 02/27/2010 for the course CHEM 140 taught by Professor Wade during the Spring '10 term at Whitman.
- Spring '10