chirality n.
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Chirality. “ chiral ”. Greek for hands. chiral =. non-superimposable mirror images. chiral =. no plane of symmetry. C *. C with 4 different substituents. stereocenter. chiral C. Chirality. H. H. *. HOH 2 C. C. CHO. OHC. C. CH 2 OH. OH. OH. enantiomers.

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chirality
Chirality

“chiral”

Greek for hands

chiral =

non-superimposable mirror images

chiral =

no plane of symmetry

C*

C with 4 different substituents

stereocenter

chiral C

chirality1
Chirality

H

H

*

HOH2C

C

CHO

OHC

C

CH2OH

OH

OH

enantiomers

non-superimposable mirror images

no plane of symmetry

3 d representations

H

*

HOH2C

C

CHO

OH

H

OH C

H

O

C

H

3-D Representations

glyceraldehyde

2,3-dihydroxy

propanal

CHO

vertical = into paper

*

H

OH

horizontal = out of paper

CH2OH

slide4

CHO

CHO

H

OH

HO

H

CH2OH

CH2OH

*

*

D-(+)-glyceraldehyde

L-(-)-glyceraldehyde

*

*

1. Most oxidized C on top

2. C* furthest from top

OH on left = L enantiomer

OH on right = D enantiomer

enantiomers
Enantiomers

identical in most properties

differ in:

1.interaction with polarized light

2. interaction with chiral environments

Light interacts with molecules

when it passes through them

[interaction of electrical fields]

When light encounters mirror image

of molecule, interaction is reversed

polarized light
Polarized light

(-)

One enantiomer -

rotate light to the left

(+)

Other enantiomer -

rotate light to the right

in 50/50 mix -

no net rotation

racemic mixture

one enantiomer -

polarized light will be rotated

optical activity

chirality2
Chirality

2. Enantiomers in chiral environments

hands

chiral

mittens

achiral -

plane of symmetry

achiral environments

don’t distinguish between enantiomers

gloves

chiral -

no plane of symmetry

chiral environments

do distinguish between enantiomers

chirality3
Chirality

caraway seed

enantiomers

of carvone

spearmint gum

Is there a C*

*

Is there a plane of symmetry

no

carvone

chirality4

CH3

CH3

O

O

*

C

H2C

CH3

C

H3C

CH2

Chirality

*

(+) carvone

(-) carvone

spearmint

caraway

rotates light to left

rotates light to right

racemic mixture - optically inactive

taste buds are chiral environment

formation of chiral compounds
Formation of chiral compounds

catalyzed by chiral enzymes

alkene + H2O

alcohol

fumerase

chiral

*

+ H2O

fumaric acid

optically inactive

COOH

*

HO

H

Malic acid

L-

CH2CO2H

optically active

slide11

carboxylic acid + alcohol

ester + H2O

O-CH3

*

*

+

+ H2O

CH3OH

D-

(-)-

lactic acid

methyl

lactate

D-

(+)-

optically active

optically active

slide12

ketone

mild reducing agent

2o alcohol

+

NaBH4

+

*

*

HO

H

H

OH

pyruvic acid

D-lactic acid

L-lactic acid

optically inactive

optically active

optically active

racemic mixture

inactive

slide13

CHO

HO

H

HO

H

CH2OH

Compounds with more than 1 C*

*

*

CHO

*

H

OH

*

H

OH

CH2OH

L-Erythrose

D-Erythrose

slide14

CHO

H

OH

HO

H

CH2OH

diastereomers

CHO

CHO

H

OH

HO

H

H

OH

HO

H

CH2OH

CH2OH

L-Erythrose

D-Erythrose

2 C*

A maximum of

2n steroisomers

*

*

*

*

enantiomers

CHO

HO

H

enantiomers

H

OH

diastereomers:

non-mirror image

stereoisomers

CH2OH

L-Threose

D-Threose

slide15

COOH

HO

H

H

OH

COOH

COOH

HO

H

HO

H

COOH

22 = 4 stereoisomers

*

*

II

I

COOH

I and II

enantiomers

H

OH

optically active

HO

H

III and IV

same

COOH

optically inactive

III

IV

meso compound

COOH

plane of symmetry

H

OH

superimposible

mirror images

H

OH

COOH