StereochemistryBy: Isman Kurniawan

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Stereochemistry

• Stereoisomers

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Chirality

• Objects that have left-handed and right-handed forms are called chiral

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Chirality

• Chirality and enantiomerism in organic molecules

• Enantiomers : nonsuperimposable mirror-image molecules

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Chirality

• Asymmetric carbon atoms

• Assymmetric/chiral carbon atom : carbon atom that is bonded to four different groups

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Chirality

• Asymmetric carbon atoms

Friday, June 20, 14

Chirality

• Asymmetric carbon atoms

• If a compound has no asymmetric carbon atom, it is usually achiral.

• If a compound has just one asymmetric carbon atom, it is chiral.

• If a compound has more than one asymmetric carbon, it may or may not be chiral.

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Exercise

• Draw a 3D structure for each compound and star all asymmetric carbon atoms. Draw the mirror image for each structure.

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Chirality

• Mirror planes of symmetry

• Any molecule that has an internal mirror plane of symmetry cannot be chiral.

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(R) and (S) Nomenclature of Asymmetric Carbon Atoms

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(R) and (S) Nomenclature of Asymmetric Carbon Atoms

• Chan-Ingold-Prelog convention

1. Assign a “priority” to each group bonded to the asymmetric carbon.

a. Atoms with higher atomic numbers receive higher priorities.

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(R) and (S) Nomenclature of Asymmetric Carbon Atoms• Chan-Ingold-Prelog convention

1. Assign a “priority to each group bonded to the asymmetric carbon.

b. In case of ties, use the next atoms along the chain of each group as tiebreakers

Friday, June 20, 14

(R) and (S) Nomenclature of Asymmetric Carbon Atoms

• Chan-Ingold-Prelog convention

1. Assign a “priority to each group bonded to the asymmetric carbon.

c. Treat double and triple bonds as if each were a bond to a separate atom

Friday, June 20, 14

(R) and (S) Nomenclature of Asymmetric Carbon Atoms

• Chan-Ingold-Prelog convention

2. Using a three dimensional drawing, put the fourth priority group in back.

3. Draw an arrow from the first priority group, through second, to the third.

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(R) and (S) Nomenclature of Asymmetric Carbon Atoms

• Chan-Ingold-Prelog convention

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Exercise

• Draw the enantiomer of 1,3-dibromobutane and label them as (R) and (S).

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Exercise

• Star (*) each asymmetric carbon atom in the following examples and determine whether it has the (R) or (S) configuration.

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Optical Activity

• Polarimetry

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Optical Activity

• Polarimetry

• Compound that rotate plane of polarized light toward the right are called dextrorotatory (d)/(+).

• Compound that rotate plane of polarized light toward the left are called levorotatory (l)/(-).

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Fischer Projections

• Drawing Fischer projections

• Uses a cross to represent an asymmetric carbon atom.

• The horizontal lines project toward the viewer, and the vertical lines project away from the viewer.

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Fischer Projections

• Drawing Fischer projections

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Exercise

• Draw a Fischer projection for each compound

a. (S)-1,2-propanediol

b. (R)-2-butanol

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Assignment

1. Star (*) any asymmetric carbon atoms. Label each asymmetric carbon as (R) or (S).

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2. Convert the following perspective formula to Fischer projections

Assignment

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3. Convert the following Fischer projections to perspective formulas

Assignment

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Assignment

• Deadline : June 25th 2014

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