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13.6 Chiral Molecules

Chapter 13 Organic Compounds with Oxygen and Sulfur

Copyright © 2005 by Pearson Education, Inc.Publishing as Benjamin Cummings

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Chiral Objects

Chiral objects• have the same number of atoms

arranged differently in space.

• have one or more chiral carbon atoms each of which is bonded to four different groups.

• are like your hands. Try to superimpose your thumbs, palms, back of hands, and little fingers.

Copyright © 2005 by Pearson Education, Inc.Publishing as Benjamin Cummings

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Mirror Images

• The mirror images of chiral compounds cannot be superimposed.

• When the H and I atoms are aligned, the Cl and Br atoms are on opposite sides.

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Achiral Structures are Superimposable

When the mirror image of an achiral structure is rotated, the structure can be aligned with the initial structure. Thus this mirror image is superimposable.

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Some Everyday Chiral and Achiral Objects

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Learning Check

Identify each as a chiral or achiral compound.

A

CH2CH3

H CH3

Cl

C

B

H

H CH3

Cl

C

C

Br

H CH3

Cl

C

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Solution

Identify each as a chiral or achiral compound.

chiral achiral chiral

A

CH2CH3

H CH3

Cl

C

B

H

H CH3

Cl

C

C

Br

H CH3

Cl

C

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Fischer Projections

A Fischer projection

• is a 2-dimensional representation of a 3-dimensional molecule.

• places the most oxidized group at the top.

• uses vertical lines in place of dashes for bonds that go back.

• uses horizontal lines in place of wedges for bonds that come forward.

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Drawing Fischer Projections

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D and L Notations

• By convention, the letter L is assigned to the structure with the —OH on the left.

• The letter D is assigned to the structure with the —OH on the right.

Copyright © 2005 by Pearson Education, Inc.Publishing as Benjamin Cummings

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Learning Check

Indicate whether each pair is a mirror image that cannot be superimposed (enantiomers).

B.

A.

and

and

Br

CH3 H

CH2OH

C

H

CH3 H

Cl

C

Br

H CH3

CH2OH

C

H

H CH3

Cl

C

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Solution

Indicate whether each pair is a mirror image that cannot be superimposed (enantiomers).

Yes

NoB.

A.

and

and

Br

CH3 H

CH2OH

C

H

CH3 H

Cl

C

Br

H CH3

CH2OH

C

H

H CH3

Cl

C