Chemistry Department

 

University of Alberta

           

CHEM 161

 

Exam II

 

November 7, 2006

 

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

 

a.       

 

                       

                        cis-4-ethoxy-2-hepten-5-yne

 

b.       

 

                       

 

                        cis-3-tert-butylcyclohexanol

 

2. The free energy difference between skew and chair cyclohexanes is usually so large that the twist conformation is not detectable.  For example, cis-1,3-di-tert-butylcyclohexane overwhelmingly favors this conformation.  However, in trans-1,3-di-tert-butylcyclohexane, the predominant conformation is the skew boat.  Explain this apparent anomaly.

 

          A chair conformation would require that one tert-butyl group be in an axial position which would result in considerable steric strain.  This strain is reduced by assuming a skew boat conformation.

 

3. 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 cis-1-chloro-4-isopropylcyclohexane:

 

                       

 

b.      Draw the most stable conformation of trans-1-chloro-4-isopropylcyclohexane:

 

                       

 

c.      Using the principles of conformational analysis (angle, torsional, and steric strain) evaluate the stability of the structures drawn in (a) and (b) above.

 

                        Both are free of angle and torsional strain. The cis isomer has the chlorine in an axial position resulting in two 1,3-diaxial H – Cl interactions and therefore 2 x 1.0 kJ/mol of strain.

 

d.      Which is the most stable structure and by how many kJ?

 

                        The trans isomer is more stable by 2.0 kJ/mol

 

4. What reagents would you use to effect the following conversions?

 

a.       

 

 

                       

 

b.       

                                                

 

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

           

           

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

 

 

 

 

7. Iodobenzene dichloride is a reagent of choice to chlorinate alkanes. Here is the equation for the overall reaction:

 

           

 

            The initiation step is shown below:

 

           

 

 

a.   Draw the transition state for this initiation process.

 

                       

 

 

b.   Explain the term “chain reaction”.

c.   Propose a chain radical mechanism for the chlorination of alkane RH by iodobenzene dichloride. The relative reactivity of the hydrogens (tertiary : secondary : primary) is 5 : 3.8 :1. 

 

                 

 

8. Explain the following terms:

 

1. inhibitor

 

2. activation energy

 

3. Lewis base

 

4. electrophile