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Chemistry, 7/e
Raymond Chang, Williams College

Visual Chemistry

Lets start by visiting the Okanagan University site at http://www.sci.ouc.bc.ca/chem/molecule/molecule.html. Go to the index of models and click on amides. When that link appears go to number 7, ethanamide, or acetamide, as it is more usually called. Now click on this molecule and you should soon see a wireframe view of it. Click and hold to see other display options (this will vary depending on browser and plug-in). Go to ball and stick and display the molecule in the way that most chemists think about molecules. Notice that you can rotate the molecule by clicking and quickly dragging the cursor. The colors of the atoms are important because they tell you what atoms are present. Generally, gray represents carbon, white represents hydrogen, blue is nitrogen, red is oxygen, and green is chlorine.
  1. Using the colors of the atoms, write the molecular formula of this molecule.
  2. Notice that while the carbon of the CH3 group has four atoms attached to it, the other carbon does not. Can you explain the bonding at this carbon? To be sure that you understand the electronic structure of this molecule write the electron-dot formula for it.
  3. Look carefully at the five atoms--H2NCO. How would you describe the geometry of these five atoms? What do the angles between the bonds seem to be?
  4. Now, go back to the index, select amines, and click on number 21, ethanamine, usually called ethyl amine. Examine the groups around the nitrogen in this molecule. How would you discribe the difference between the geometry at this site compared with the nitrogen in acetamide?
  5. With ethyl amine in front of you, change the display mode to space-fill using van der Waals radii. Then return to ball and stick display and use the option menu to go to dot surface using van der Waals radii. What do you suppose the space-filling and dot surface models are meant to represent?
  6. Now go to the molecular viewing gallery at http://www.dcu.ie/%7Echemist/pratt/pdb/gallery.htm:
  7. Examine adamantane and determine its molecular formula, its empirical formula, and draw a line formula for it.
  8. Look at boron trfluoride and determine the geometry of this molecule.
  9. A plane of symmetry is a hypothetical plane that can be drawn through a molecule such that the parts of the molecule on both sides of the plane are mirror images of one another. For example, in BF3, there is a plane perpendicular to the plane of the molecule passing through one fluorine and the boron. On one side of this plane there is a fluorine. Imagine that the plane is a mirror. When you look into the mirror from the side of this fluorine the image that you see is exactly what the fluorine on the other side of plane looks like. How many planes of symmetry are there in the molecule?
  10. Now examine the boron trifluoride-ammonia complex. Have the bond angles around the boron changed relative to those in boron trifluoride?
  11. Examine bicyclo[2,2,2]octane. How many six membered rings are there in this molecule? How many planes of symmetry can you find in this molecule?
  12. Take a close look at Z-but-2-ene and E-but-2-ene. Write the structural formula for each molecule. Are these really different molecules? Do these two compounds have different boiling points, different refractive indices, etc.?
  13. Now look at butane (staggered), butane (ecclipsed), and butane (gauche). Write the structural formula for each of these molecules. Are these different molecules? How do these molecules differ from one another? What is ecclipsed in the ecclipsed molecule?
  14. What are the bond angles at each of the carbons in cyclohexanone? To what hybridization do these angles correspond? Can you find a plane of symmetry in this molecule?
  15. Cubane was first prepared about 30 years ago after chemists had tried for many years to prepare it. What are the bond angles at each carbon? What were the bond angles in the other hydrocarbons you have examined? Why might cubane be difficult to prepare?
  16. Look at iso-butyl propionate and n-butyl propionate. What is the difference between the two molecules? Can you find another ester [the functional group in these molecules is the ester group] that also contains an iso group?
  17. Take a look at t-butyl acetate and compare it with the two esters in part 10. What is the difference between these three butyl groups?
  18. Write the molecular formula for naphthalene. How would you describe the geometry of this molecule? How many planes of symmetry can you locate?
  19. How would you describe the geometry of phosphorus pentachloride? If one of the chlorines were replace by a bromine, how many different molecules would there be?
  20. Do any of the atoms in pyridine have a lone pair of electrons? Molecules that can donate a pair of electrons are said to be Lewis bases or nucleophiles; molecules that can accept a pair of electrons are Lewis acids or electrophiles. Is pyridine a Lewis acid or a Lewis base?
  21. Molecules that have a hydrogen attached to oxygen or nitrogen or fluorine usually have fairly strong forces between them. These forces are called hydrogen-bonding. The hydrogen of one molecule acts as a Lewis acid or electrophile toward a neighboring molecule, which donates electron density (acts as a nucleophile) from a lone pair to the hydrogen. Does salicylic acid exhibit hydrogen bonding? Can you find the nucleophilic sites on the salicylic acid?








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