Chemistry Department

 

University of Alberta

           

CHEM 161

 

Exam II

 

November 8, 2005

 

1. The following table lists the steric strain due to one hydrogen - substituent 1,3-diaxial interaction in some monosubstituted cyclohexanes:

 

 

 

a.      Draw the most stable conformation of trans-1-chloro-3-methylcyclohexane:

 

 

b.      Justify your decision using the principles of conformational analysis.

 

Both possible conformations are free of angle strain and of torsional strain.  However the steric strain due to two H – Cl 1,3-diaxial interactions is 2.0 kJ/mol whereas that due to two H – CH₃ 1,3-diaxial interactions is 7.6 kJ/mol

 

c.      One of the two chair structures of cis-1-chloro-3-methylcyclohexane is more stable than the other by 15.5 kJ/mol. Draw the structure of the more stable structure.

 

 

d.      Calculate the energy cost of a 1,3-diaxial interaction between a chlorine and a methyl group.

 

            15.5 - 1.0 – 3.8 = 10.7 kJ/mol

 

2. Using acceptable chemical nomenclature, provide an unambiguous name for the following compounds:

 

a.       

 

                       

 

                        cis-4-tert-butylcyclohexanol

 

b.       

 

                       

 

                        trans-1-methoxy-2-pentene

 

3. What reagents would you use to effect the following conversion?

                       

           

 

4. Give the major product(s) of the following reaction:

 

           

 

           

 

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

 

1.  

 

 

 

2.  

 

 

 

6. AIBN, azobisisobutyronitrile, is an initiator of radical reactions.  It undergoes thermal homolysis at 60°C as follows:

 

           

 

a.   Draw the transition state for this process.

 

                       

 

b.   Explain the term “chain reaction”.

 

                        A chain reaction involves a series of steps.  Each one generates a reactive species that brings about the next step.

 

c.   The tributylstannane reacts with alkyl halides by a radical, chain mechanism initiated by AIBN. Given the representative bond energies: C – Br 280 kJ/mol, Sn – H 308 kJ/mol, C – H 418 kJ/mol, Sn – Br 552 kJ/mol, propose a mechanism for the following reaction:

 

                       

 

                                   

 

7. Explain the following terms:

 

1. rate determining step

 

2. activation energy

 

3. conformation

 

4. Lewis acid