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Stereochemistry

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The two structures are enantiomers of each ... trigonal planar. tetrahedral centers. Enantiomers exist when two structures have the maximum number of differing ... – PowerPoint PPT presentation

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Title: Stereochemistry


1
Stereochemistry
2
Review of Stereoisomers
cis-2-butene
trans-2-butene
3
cis-1,2-difluorocyclohexane
trans-1,2-difluorocyclohexane
4
What are the following?
5
After rotating the one on the right.
6
You can see that the two structures do not
overlap...
7
The two structures are enantiomers of each other
  • Non-superimposable mirror images.

8
Why do enantiomers exist?
  • Linear
  • trigonal planar
  • tetrahedral centers

9
Enantiomers exist when two structures have the
maximum number of differing groups attached to
the center atom (I.e. carbon has 4 different
groups).Opposite enantiomers have the groups
attached different ways.Each is a mirror image
of the other, and neither are superimposable on
each other.
10
Definitions
  • Chiral Carbon a carbon with four different
    groups attached to it.
  • Chiral object an object or compound that
    contains at least one chiral center

11
How can you tell the difference?
  • Using the Cahn-Ingold-Prelog rules, the groups
    attached to the center carbon are ranked.
  • These groups are determined to be attached in a
    clockwise fashion. R or a
    counterclockwise fashion. S

12
Dealing with Stereochemistry
  • How to assign R and S configurations from a
    structure.
  • How to assign R and S configurations from a
    Fisher Projection.
  • Having Greater than One Chiral Center
  • Diastereomers
  • Meso Compounds

13
Bromine red Chlorine blue Fluorine green Hydrogen
white
Br
Rotate the molecule so that the lowest group is
in the back...

Cl
F
H
14
Br
F
Cl

Connecting bromine to chlorine to fluorine takes
you counterclockwise, so this structure would be
S
15
Using Spartan to view enatiomers...
  • Click here to go to spartan.

16
Drawings
17
Fisher Projections
  • Originally designed to help aid in the
    determination of sugar molecules
  • It flattens out the chiral carbon (so you dont
    have to use the dimensional analysis).

18
Br
Rotate the molecule so that the horizontal
groups are coming out toward you like a hug...
F
Cl
H

The Fisher Projection from the view shown...
19
Fisher Projections
20
Are these Fisher Projections of the same compound?
  • Determine the Configuration of each one
  • If one is R and one is S they are enantiomers.
  • If both are the same, they are the same
    compound.

21
With more than one stereocenter, there are other
relationships
  • Enantiomers are non-superimposible mirror images
    of each other. No matter how many stereogenic
    centers (chiral carbons), all are opposite in
    enantiomers.
  • Diasteriomers are stereoisomers that are not
    mirror images of each other. (They have opposite
    configurations at some centers, but have the same
    configurations at others).

22
Examples
  • Easy to tell....

23
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24
Meso Compounds...
  • ------------------------------------------
  • Contain a Plane of Symmetry through the middle of
    the compound

25
Enantiomers or Diasteriomers?
26
Group Problem Session
27
Newman Projections view a carbon-carbon bond
from the side. The carbon in the background
winds up straight behind the carbon in the
foreground.
28
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29
Geometry of Propane
Best Geometry is Staggered
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