1

12.6 Chiral Molecules

Chapter 12 Organic Compounds with Oxygen and Sulfur

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

2

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

3

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.

4

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.

5

Some Everyday Chiral and Achiral Objects

6

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

7

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

8

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.

9

Drawing Fischer Projections

10

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

11

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

12

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

13

Good practice problems

Draw a star on the carbon atoms to denote chirality in menthol (peppermint)

OH

14

Answer:

There are three chiral carbon atoms in menthol (peppermint)

OH

*

**

15

Try this popular antidepressant

Zoloft (Sertraline)HN

Cl

Cl

16

Answer

Two HN

Cl

Cl

*

*

17

Try the following

Lipitor (atorvastatin)

N

OH

HO O

O-

HN

O

F

Ca2+

2

18

Answer

Two

N

OH

HO O

O-

HN

O

F

Ca2+

2

*

*

19

Another anticholesterol drug

Zocor

O

OH3C

H3C CH3

O

H3C

HO

CH3

H

O

20

Answer

Seven

O

OH3C

H3C CH3

O

H3C

HO

CH3

H

O

**

*****

21

Chapter 13 Carboxylic Acids, Esters, Amines, and Amides

13.1 Carboxylic Acids

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

22

A carboxylic acid contains a carboxyl group, which• is a carbonyl group (C=O) attached to a hydroxyl

group (—OH).• is found on carbon 1 in carboxylic acids.

O

CH3 — C—OH hydroxyl group or CH3COOH

carbonyl group

Carboxylic Acids

23

Models of Carboxylic Acids

The three-dimensional models show the geometry of atoms in carboxylic acid molecules.

24

The IUPAC names of carboxylic acids:

• Replace the -e in the alkane name with -oic acid.

CH4 methane HCOOH methanoic acid

CH3—CH3 ethane CH3—COOH ethanoic acid

• Number substituents from the carboxyl carbon 1.

CH3 O | ║

CH3—CH—CH2—C—OH 4 3 2 1

3-methylbutanoic acid

IUPAC Names

25

Names and Sources of Some Carboxylic Acids

26

Common Carboxylic Acids

Methanoic acid (formic acid)

O

║

H─C─OH

ethanoic acid (acetic acid)

O

║

CH3─C─OH

27

Aromatic Carboxylic Acids

Benzoic acid• is the aromatic

carboxylic acid.

• locates substituents by numbering the ring from carbon 1 in the carboxyl group.

OHC

O

OHC

O

OHC

O

ClNH2

3-chlorobenzoic acid 4-aminobenzoic acid

benzoic acid

28

Learning Check

Give the IUPAC names of each compound. A. CH3─CH2─COOH

CH3

|

B. CH3─CH─CH2─COOHC.

OHC

O

Br

29

Solution

A. CH3─CH2─COOH propanoic acid

CH3

|

B. CH3─CH─CH2─COOH 3-methylbutanoic acid

C. 3-bromobenzoic acid OHC

O

Br