Chapter 9
Content
Chapter 9 Review Sheet - Stereochemistry Important Definitions
Chiral carbon: also known as asymmetric carbon or chirality center; a carbon atom with four different substituents surrounding it; must have sp3 hybridization Enantiomer: a non-superimposable, mirror-image; must have at least one chiral carbon Diastereomer: a non-superimposable, non-mirror image; must have more than one chiral carbon; for n chiral carbons in a molecule there are 2n diastereomers; includes cis and trans isomers of alkenes Meso: molecules containing more than one chiral carbon but are overall achiral because of the presence of a plane of symmetry Chiral: the property of a molecule such that it rotates plane polarized light in a particular direction Achiral: molecules that do not rotate plane polarized light
Fisher Projections
A D C B
Substituents on the vertical line are directed into the page away from the viewer.
Look down on molecule from here to see the Fisher model
Substituents on the horizontal line are directed out of the page toward the viewer.
D A
B C
BUILD THE MODEL AND YOU WILL SEE IT!
Basic Rules of Fisher Projections
1. If you switch the positions of any two substituents that are attached to the same carbon, then the absolute configuration of that carbon (R or S) is switched. 2. If you switch the positions of any two substituents that are attached to the same carbon, and then switch two more substituents (on that same carbon), the absolute configuration does not change. 3. In summary, an even number of switches conserves the absolute configuration while an odd number of switches changes the absolute configuration. 4. Rotating the Fisher projection 90 degrees switches the absolute configuration. 5. Rotating the Fisher projection by 180 degrees conserves the absolute configuration.
A D C B
switch A and B
B D C A
switch B and C
C D B A
S
A D C B
R
rotate 90 deg.
D C B A
S
rotate 90 deg.
C B A D
Diastereomers
CH3 Br Cl I F CH3
enantiomers
CH3 Cl Br F I CH3
diastereomers
diastereomers
diastereomers
CH3 Cl I CH3
Cl I
CH3 Br F CH3
enantiomers
Br F
There are two pairs of enantiomers and four pairs of diastereomers
No Chiral Centers!
No Chiral Centers!
Chiral carbon: also known as asymmetric carbon or chirality center; a carbon atom with four different substituents surrounding it; must have sp3 hybridization Enantiomer: a non-superimposable, mirror-image; must have at least one chiral carbon Diastereomer: a non-superimposable, non-mirror image; must have more than one chiral carbon; for n chiral carbons in a molecule there are 2n diastereomers; includes cis and trans isomers of alkenes Meso: molecules containing more than one chiral carbon but are overall achiral because of the presence of a plane of symmetry Chiral: the property of a molecule such that it rotates plane polarized light in a particular direction Achiral: molecules that do not rotate plane polarized light
Fisher Projections
A D C B
Substituents on the vertical line are directed into the page away from the viewer.
Look down on molecule from here to see the Fisher model
Substituents on the horizontal line are directed out of the page toward the viewer.
D A
B C
BUILD THE MODEL AND YOU WILL SEE IT!
Basic Rules of Fisher Projections
1. If you switch the positions of any two substituents that are attached to the same carbon, then the absolute configuration of that carbon (R or S) is switched. 2. If you switch the positions of any two substituents that are attached to the same carbon, and then switch two more substituents (on that same carbon), the absolute configuration does not change. 3. In summary, an even number of switches conserves the absolute configuration while an odd number of switches changes the absolute configuration. 4. Rotating the Fisher projection 90 degrees switches the absolute configuration. 5. Rotating the Fisher projection by 180 degrees conserves the absolute configuration.
A D C B
switch A and B
B D C A
switch B and C
C D B A
S
A D C B
R
rotate 90 deg.
D C B A
S
rotate 90 deg.
C B A D
Diastereomers
CH3 Br Cl I F CH3
enantiomers
CH3 Cl Br F I CH3
diastereomers
diastereomers
diastereomers
CH3 Cl I CH3
Cl I
CH3 Br F CH3
enantiomers
Br F
There are two pairs of enantiomers and four pairs of diastereomers
No Chiral Centers!
No Chiral Centers!
