Molecular Models 2
Chem 102, Fall 2005
Name ___________________________________
Important Definitions:
Plane of symmetry: A plane that passes through an object such that the part on one side
of the plane is the exact mirror reflection of the part on the other side.
Superimposable: Two objects are superimposable if when they are put together in
space all parts of each object coincide. If two objects are superimposable they are
identical.
Chiral: Containing the properties of "handedness." A chiral object is not
superimposable upon its mirror image. A chiral carbon has 4 different groups
attached.
Isomers: Two or more molecules that have identical molecular formulas, but different
arrangements of their atoms.
Stereoisomers: Isomers having the same sequence of atoms and bonds, but differing in
the fixed three-dimensional arrangement of these atoms. Stereoisomers may have
different physical and chemical properties.
Enantiomers: Stereoisomers that are mirror images of each other.
Diastereomers: Stereoisomers that are not mirror images of each other.
Molecules with One Chiral Carbon:
Construct a model containing a tetrahedral carbon (black ball) with four different atoms
attached (use the green, orange, purple and white balls). This model will be referred to
as A.
1. Make a sketch of A using wedges and dashes. Does A have any planes of symmetry?
If yes, draw their positions.
2. Construct a model that is the mirror image of A. This model will be referred to as B.
Make a sketch of B using wedges and dashes. Are A and B mirror images? Are A and
B superimposable?
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3. Are A and/or B chiral?
4. What is the relationship between A and B (enantiomers, diastereomers, identical)?
5. Switch the white and green balls on B. This model will be referred to as C. Are A
and C mirror images? Are A and C superimposable?
6. What is the relationship between A and C (enantiomers, diastereomers, identical)?
7. What is required to convert one enantiomer into its mirror image?
8. Replace the green atoms in A and C with white atoms to give models referred to as D
and E. Make a sketch of D using wedges and dashes. Does D have any planes of
symmetry? If yes, draw their positions.
9. Are D and E mirror images? Are D and E superimposable?
10. Are D and/or E chiral?
11. What is the relationship between D and E (enantiomers, diastereomers, identical)?
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12. How many different groups does a carbon need to be chiral?
Molecules with Two Chiral Carbons:
Construct a model with four different atoms attached to carbon. Use white, green,
orange and red balls to represent the different atoms. Make another model that is
identical with the first (make sure they are superimposable). Remove the orange atom
from both models and connect the two carbon atoms with a bond. This model contains
two chiral carbons. It will be referred to as F.
13. Do any of the conformations of F contain a plane of symmetry? (Rotate about the
carbon-carbon bond to observe the different possible conformations). Make a sketch of
F using wedges and dashes and draw the location of any planes of symmetry. Also
draw the Fischer projection of F.
Construct a model of the mirror image of F. This model will be referred to as G.
14. Are F and G mirror images? Are F and G superimposable?
15. Are F and/or G chiral?
16. What is the relationship between F and G (enantiomers, diastereomers, identical)?
Exchange the white and green atoms on one of the carbon atoms on G. This model will
be referred to as H.
17. Do any of the conformations of H contain a plane of symmetry? (Rotate about the
carbon-carbon bond to observe the different possible conformations). Make a sketch of
H using wedges and dashes and draw the location of any planes of symmetry. Also
draw the Fischer projection of H.
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18. Are F and H mirror images? Are F and H superimposable?
19. What is the relationship between F and H (enantiomers, diastereomers, identical)?
Construct the mirror image of H. This will be referred to as I.
20. What is the relationship between H and I (enantiomers, diastereomers, identical)?
21. Are H and/or I chiral?
22. How many "chiral" carbons does H contain?
23. What is the relationship between H and G (enantiomers, diastereomers, identical)?
24. Draw all the possible stereoisomers of 2,3-dichlorobutane. Label them (A, B, etc.)
and identify any enantiomers or diastereomers.
25. Draw all the stereoisomers of 2-bromo-3-chlorobutane. Label them (A, B, etc.) and
identify any enantiomers or diastereomers.
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