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Unformatted text preview: CHEM 231 Stereochemistry II LECTURE 9 LECTURE 9 1 Review of why stereochemistry is important
Organic compounds are 3dimensional sp hybridized carbons are what makes them Lecture 9 2 How do you name molecules with chiral centers
CH3 Cl F
Many students asked about how to utilize cistrans nomenclature to describe a compound such as this We will utilize the CahnIngoldPrelog rules in a new setting to give accurate names to structures like the one above.
Lecture 9 3 CahnIngoldPrelog Rules: A review First comparison in ranking is atomic number Sometimes groups have the same atomic number but not the same mass Often 2 groups on the alkene are identical. To solve this follow bonds away from alkene to determine rank Multiple bonds get counted as multiple single bonds Lecture 9 4 Determination of absolute configuration of a drawn compound using CIP:
1 Cl 3 H 4 F2 Rank each group relative to each other. Each of these can be ranked based on the first CIP rule Chlorine has the highest atomic numberthus it has the highest priority Highest priority =1; lowest priority = 4
Lecture 9 5 Determination of absolute configuration of a drawn compound using CIP
1 Cl 3
We ignore group 4 We track the trend from highest priority to third priority H 4 F2 We observe in which general direction groups 1,2 3 trend. Lecture 9 6 Determination of absolute configuration of a drawn compound using CIP
1 Cl 3
The counterclockwise trend indicates that this molecule is an (S) molecule This is related to the latin, sinister, which means left handed H 4 F2 counterclockwise trend The molecule is (S)1chloro1fluoroethane Lecture 9 7 Lets do some other examples I Cl H Br CH3 Br H I Cl
8 Lecture 9 Using models to simplify determinations Br
4H 2 Cl 3 I
1 Lecture 9 9 Using models to simplify determinations 1 Br F 4 H3C
C H2 2 CH3 H 4 Cl 3 3 2 1 Lecture 9 10 Assigning absolute configuration to cyclic compounds
H CH3 Cl 2 4 H CH 3 3 1 Cl Cl Cl Lecture 9 11 Assigning absolute configuration to cyclic compounds
H3C H H3C H H3C H H H3C H CH3 H CH3 Lecture 9 12 Chirality with heteroatomic centers
Any central atom with 4 different groups is CHIRAL N Cl F Br O P O O NH S H3 C H Si Lecture 9 13 ...
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