Chemistry Department

 

University of Alberta

           

CHEM 261

 

Final Exam

 

May 28, 2010

 

1. Name the following compounds by the IUPAC system. The name must indicate the stereochemistry of the compound. (12 points)

 

a.     

 

 

b.     

 

 

c.     

 

                                   

                                   

2. Complete the following partial Fischer structure of meso-3,4-dibromohexane: (4 points)

 

 

3. Complete the following partial structure of (E,5R)-5-bromo-3,6-dimethyl-3-heptene: (5 points)

 

 

        

 

4. Give the structure(s) of the major organic products of five (5) of the following reactions:

 

a.     

 

 

b.     

 

                                                          

c.     

 

 

d.     

 

 

e.     

       

 

f.      

 

 

5. What reagents would you use to effect five (5) of the following conversions?

 

a.     

 

 

b.     

 

 

c.     

 

 

d.     

 

 

e.     

 

 

f.      

 

 

6. Provide a synthetic pathway for the following transformations.  Begin your synthesis with the indicated starting material.

 

a.    (10 points)

 

 

b.    (8 points)

 

 

7.  

a.    Select the member of each pair of compounds that will react faster by an S_N2 mechanism: (2 points)

 

                              i.        CH₃CH₂CH₂CH₂NH₂ or CH₃CH₂CH₂CH₂F

 

                            ii.        CH₃CH₂CH₂CH₂Cl or CH₃CH₂CH₂CH₂Br

 

b.    Which S_N2 reaction of each pair would you expect to take place more readily in a protic solvent? (2 points)

 

                              i.        CH₃CH₂CH₂Cl + (CH₃)₂S ® CH₃CH₂CH₂S(CH₃)₂⁺ + Cl^-

or

CH₃CH₂CH₂Cl + (CH₃)₂O  ® CH₃CH₂CH₂O(CH₃)₂⁺  + Cl^-

                               

                            ii.        CH₃CH₂CH₂Cl + CH₃CH₂OH ® CH₃CH₂CH₂OCH₂CH₃ + Cl^-

or

CH₃CH₂CH₂Cl + CH₃CH₂O^- ® CH₃CH₂CH₂OCH₂CH₃ + HCl

 

c.    Which S_N1 reaction of each pair would you expect to take place more rapidly? : (2 points)

 

                              i.        (CH₃)₃CF + H₂O ® (CH₃)₃COH + HF

or

(CH₃)₃CCl + H₂O ® (CH₃)₃COH + HCl

                       

                            ii.        (CH₃)₂CHBr + H₂O ® (CH₃)₂CHOH + HBr

or

(CH₃)₃CBr + H₂O ® (CH₃)₃COH + HBr

 

d.    1-Bromopropane reacts with an aqueous solution of sodium hydroxide to form 1-propanol.

 

                              i.        Draw the most likely mechanism for this reaction.  (Don’t forget the curved arrows). (3 points)

 

                            ii.        If potassium iodide is added to the reaction mixture, the rate of formation of the 1-propanol is enhanced. Explain what takes place. (3 points)

 

e.       3,3-Dimethyl-2-butanol reacts with HCl to form 2-chloro-2,3-dimethylbutane. Draw the most likely mechanism for this reaction.  (Don’t forget the curved arrows). (8 points)

 

8. When the deuterium-labeled compound shown below is subjected to dehydrohalogenation using sodium ethoxide in ethanol, the only alkene product is 3-methylcyclohexene.  The product contains no deuterium.

 

 

a.    What is a deuterium isotope effect? (2 points)

 

b.    Draw the most likely mechanism for this reaction and explain why the deuterium is lost.  (Don’t forget the curved arrows). (9 points)

 

9. 1-Methyl-1-vinylcyclopentane reacts with HCl to form 1-chloro-1,2-dimethylcyclohexane. Propose a mechanism to account for this behaviour. (Don’t forget the curved arrows). (9 points)

                 

10. At the beginning of the biogenesis of squalene isopentenyl pyrophosphate, CH₂=C(CH₃)CH₂CH₂OPP, is enzymatically isomerized to dimethylallyl pyrophosphate, (CH₃)₂C=CHCH₂OPP.  These two compounds then react together to yield geranyl pyrophosphate,  (CH₃)₂C=CHCH₂CH₂(CH₃)C=CHCH₂OPP.  Assuming that the weakly basic pyrophosphate anion is, like the protonated hydroxyl group, a good leaving group, R-OPP ® R⁺ + OPP^- suggest a mechanism by which geranyl pyrophosphate might be formed. (Don’t forget the curved arrows). (9 points)

 

11. Caryophyllene, C₁₅H₂₄, is a terpene which largely responsible for the odor associated with cloves.  Catalytic hydrogenation gives a compound of formula C₁₅H₂₈.

 

a.    How many units of unsaturation are present in caryophyllene? (1 point)

 

b.    How many rings are present in caryophyllene?  (1 point)

 

Ozonolysis of caryophyllene gives formaldehyde, H₂C=O, and the following compound:

 

 

 

c.    How many double bonds are present in caryophyllene?  (1 point)

 

Hydroboration of caryophyllene with one equivalent of diborane followed by ozonolysis yields:

 

 

 

d.    Draw the structure of caryophyllene.  (4 points)