Molecular Modeling Exercise II

Chemistry 231 – SSCC

11-13-06

Names______

Turn in only 1 sheet per group.

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 molecule coincide. They are identical molecules.
  • Chiral: An object that possesses the property of “handedness”. A chiral object is not superimposable upon its mirror image.
  • Isomers: Molecules that have the same molecular formula, but differ in the arrangement of atoms.
  • Constitutional Isomers: Molecules that have the same molecular formula, but different connectivity of atoms.
  • Stereoisomers: Molecules that have the same sequence of atoms and bonds, but differ in their arrangement in space. Stereoisomers are only interconvertible by breaking and making bonds. Stereoisomers are not constitutional isomers.
  • Enantiomers: Stereoisomers that are nonsuperimposable mirror images of each other.
  • Diastereomers: Stereoisomers that are not mirror images of each other.

Stereoisomerism

Construct a model containing a tetrahedral carbon (black ball) attached to four different atoms (use green, orange, purple and white balls). This model will be referred to as ModelA.

  1. Does Model A have any planes of symmetry? If yes, draw their positions.

No planes of symmetry.

Construct a model that is the mirror image of Model A. This model will be referred to as Model B.

  1. Are Model A and Model B superimposable or are they mirror images? Mirror images
  1. Is Model A chiral? YesIs Model B chiral? Yes
  1. What is the relationship between Model A and Model B (enantiomers, diastereomers, or identical?)

enantiomers

Switch the white and green balls on Model B. This model will be referred to as Model C.

  1. Are Model A and Model C superimposable or are they mirror images? superimposable
  1. What is the relationship between Model A and Model C (enantiomers, diastereomers, or identical?)

identical

  1. What is required to convert one enantiomer into its mirror image?

Break bonds and switch two atoms

Replace the green atoms in Model A and Model C with white atoms to give Models D and E. Now there are only three different groups attached to each carbon.

  1. Are Model D and Model E superimposable? Yes
  1. Are Model D and Model E mirror images of each other? Yes
  1. Does Model D have a plane of symmetry? If so, draw its location.

Plane of symmetry in the plane of the paper.

  1. Is Model D or E chiral? No
  1. What is the relationship between Models D and E (enantiomers, diastereomers, or identical?)

identical

  1. How many different groups does a carbon need to be chiral? 4

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 atoms from both models and connect the two carbon atoms with a bond. This model contains two chiral carbons. It will be referred to as Model F.

  1. Do any of the conformations of Model F contain a plane of symmetry? If yes, draw their location. (You may rotate about the carbon-carbon bond to observe the different possible conformations). NO

Construct a model of he mirror image of Model F. This will be referred to as Model G.

  1. Are Model F and Model G superimposable? NO
  1. Is Model F or Model G chiral? Both are chiral.
  1. What is the relationship between Models F and G (enantiomers, diastereomers, or identical?)

enantiomers

For Model G, exchange the white and green atoms on one of the carbon atoms. This will be referred to as Model H.

  1. Are Model F and Model H mirror images? NO
  1. What is the relationship between Models F and H (enantiomers, diastereomers, or identical?)

Diastereomers

Construct the mirror image of Model H. This will be referred to as Model I.

  1. Do any of the conformations of Model H contain a plane of symmetry? If yes, draw their location. (You may rotate the carbon-carbon bond to observe the different conformations).
  1. What is the relationship between Models H and I (enantiomers, diastereomers, or identical?)

Identical

  1. How many chiral carbons does Model H contain? 2
  1. Is Model H or Model I chiral? NO, there is a plane of symmetry through each molecule.
  1. Draw all the stereoisomers of 2,3-difluorobutane.

A and B are diastereomers

A and C are diastereomers

B and C are enantiomers

  1. Draw all the stereoisomers of 2-bromo-3-iodobutane.

A and B are enantiomers

A and C, A and D, B and C, B and D are diastereomers

C and D are enantiomers

  1. If carbon atoms were planar (flat) and had 90 angles would the compound below have an enantiomer? A diastereomer? If yes, depict them.

No enantiomers, all three above are diastereomers.

Make the model of the allene shown below.

  1. Draw all the stereoisomers of the allene.
  1. What is the relationship of the stereoisomers depicted? Enantiomers