Building Isomers: Complexity and Connectivity in Organic Chemistry”                              Unit 11 Lab Exercise                                                                                                                                                     NAME:__________________

Background: As we have discussed in class, the complexity of organic chemistry comes from the ability of carbon containing compounds to form isomers.  Complexity also comes from the presence of other covalently bonded atoms like oxygen or nitrogen.

Objectives:

1.      Build models of simple organic compounds and observe their shape.

2.      Draw structural models of the compounds you build.

3.      Draw and build a number of isomers from a given molecular formula.

Instructions and Questions: (Instructions are numbered and questions are lettered.)

1.      Pentane is a saturated hydrocarbon with five carbons in a row.  Build pentane.

(a)    How many hydrogens does pentane have?

(b)   Write the molecular formula of pentane.

2.      Using the same collection of atoms you have for pentane, build two more structural isomers.

(a)    Draw pentane and its two other structural isomers.  (Typically the atoms are represented by their symbols “C” and “H” and the “stick” bonds are drawn as lines.)

 (b)   Is it possible to build a compound with all the components you used in steps 1 & 2 and have a carbon-carbon double bond (C==C?)

 (c)    If you make a C==C, double bond, how many hydrogens would your 5-carbon molecule have?

 (d)   What does this illuminate about the terms “saturated” and “unsaturated” hydrocarbons?

 3.      Now add a “red” oxygen atom. 

(a)    How many different ways can you attach the oxygen to your 5 carbons and ___ hydrogens?  (Remember how many bonds oxygen likes to have.  The holes are helpful here.)

(b)   Draw four of these that are obviously different from each other.

(c)    What is the name of one of the functional groups that you have made with this additional oxygen?

(d)   What bond angle would you estimate is formed between the elements attached to carbon?

(e)    Consider the polarity of the bonds between the oxygen and the carbon and/or hydrogen to which the oxygen is attached.  How would the following properties: water solubility, boiling point and state at room temperature, be different for the oxygen containing compounds versus the pentane you made earlier?  Explain.

4.      Now select the following atoms, C₃H₆O₂.  Build  then draw in the spaces below 5 different molecular structures according to the given description.  Be sure that all the bonding rules are followed.  Sketch the molecules with the appropriate geometry as best that you can.  Note: in all your structures, avoid bonding O to O.  The O—O single bond is very unstable.  

(i) A carboxylic acid                                    (ii) a cyclic molecule (in a ring)

 (iii) a “double alcohol” (diol)                      (iv) a single alcohol

 (v) a molecule that doesn’t fit any of the descriptions above.

 (a)     Could you fill all the bonding sites (i.e. holes in the atoms) using only single bonds and sticks  in your models?

 (b)    Were any of your models too strained when you tried to use sticks?             Assuming that the bond angles between holes are correct for the way the atoms bond, what do these “strained” bonds tell you about the bonds in the real molecules?

 5.      Now select the following atoms, C₂H₇N.  Build  then draw in the spaces below 2 different molecular structures according to the given description.  Remember how many bonds Nitrogen gets.  Sketch the molecules with the appropriate geometry as best that you can.

 (a)    Which of the two structures would be better able to hydrogen bond to another like molecule?  Explain in terms of how easily the hydrogen bonding parts on two such molecules could approach each other.

(b)   Such nitrogen containing organic compounds act as bases when dissolved in water.  Show with a drawing of the molecule and water how this basic character might be explained.  (Hint: Think Bronsted-Lowry base)