1.    (12+6+6+5 = 29)  Consider the following ion.  (You should know the location of any lone pairs of electrons before answering the questions.)

                                                                    +

                                                   CH2=CH–O=CH2     

                                                      A      B      C     D

 

       a.    Indicate the hybridization at each atom (except hydrogen).

 

               A     __sp2___

 

               B     __sp2___

              

               C    __sp2___

 

               D    __sp2___

 

       b.    Draw a top view that shows the correct geometry of this planar ion.  All the bond angles should be shown.  (Solid lines, only, are needed.)

                                           

                                           

 

       c.    Draw a side view of the plane of the ion.  Indicate the geometry with wedges and hashed lines where needed.  Place a p orbital (with top and bottom lobes drawn) on each atom that has one.  The p orbitals should be vertical.

 

                            

 

       d.    Draw one low energy resonance form for the cation below.  Add the unshared electrons on this structure before drawing the resonance form.  Show the curved arrow(s) needed to generate the new resonance form.

                                           CH2=CH–O=CH2  ↔          

 

 

 

2.    (12)        Draw two isomers with the molecular formula, C4H6, both of which have four different carbon atoms (i.e. each isomer gives four 13C nmr signals).

 

                     

 

 

3.    (12)  Draw the structure of (2R,3Z)-2-fluoro-3-hexene.

                                   

                                   

 

4.    (10)        Draw the most stable conformation of 1-chloro-2-methylpropane.  Use a Newman projection that looks along the C1-C2 bond.

 

                            

 

5.    (5)   The heat of formation of propyne is about + 45 kcal/mol.  Propadiene is

3 kcal/mole less stable than propyne.  What is the heat of formation of propadiene?

 

 

                                    ___48_____ kcal/mol

 

 

6.    (6)   Why is ethyne (HCΞCH) more acidic than methane?

The conjugate base of ethyne is more stable than the conjugate base of methane because the unshared electrons in the ethynyl anion occupy an sp orbital.  The sp orbital has more s character than does the sp3 orbital of the methyl anion.  As a result the ethynyl anion is more stable than the methyl anion (relative to the corresponding acids.

              

 

7.    (10)  Using asterisks, indicate all the stereogenic carbon centers in the penicillin below.

                                   

 

8.    (5)   What is the relationship between compounds A and B? 

 

                            

                                                   A                                                B

              

Are they        A.    identical      

                      B.    diastereomers                          Answer:___enantiomers___________

                      C.   enantiomers       

                      D.   meso compounds

 

 

9.    a.    (6)  Draw a stereoisomer of          

                                           

                                  

                                   

 

 

       b.    (5)   What is the relationship between these two stereoisomers?

 

Are they:       A.    identical      

                      B.    diastereomers                          Answer:____Disastereomers_______

                      C.   enantiomers       

                      D.   meso compounds