Chemistry Department

 

University of Alberta

           

CHEM X61

 

Exam II

 

May 18, 2006

                                                                       

  1. Draw the structure of oxacyclopentane.

 

           

 

  1. Complete the following partial structure of the most stable conformation of cis-4-ethoxycyclohexanol:

 

           

 

               

 

  1. Using the following partial Newman projection formula, draw the most stable conformation of 1-bromo-1,2-dichloroethane.

 

 

 

  1. Name the following compounds:

 

    1.  

 

 

9-methylbicyclo[4.2.1]nonane 

    1.  

 

 

5-butyl-3,8-dimethyldecane 

    1.  

 

                       

 

                        cis-3-tert-butylcyclohexanol 

 

  1. The following table lists the steric strain values for one H-substituent 1,3-diaxial interaction.  Thus the value of a H-F 1,3-diaxial interaction is 0.5 kJ/mol.

            

substituent

strain (kJ/mol)

substituent

strain (kJ/mol)

Br-

1.0

C6H5-

6.3

CH3-

3.8

Cl-

1.0

CH3CH2-

4.0

CN-

0.4

(CH3)2CH-

4.6

HO2C-

2.9

(CH3)3C-

11.4

F-

0.5

 

 

a.      Draw the more stable chair conformation of trans-1-t-butyl-4-methylcyclohexane.

 

                       

 

b.      Draw the possible chair conformations of cis-1-t-butyl-4-methylcyclohexane.

 

                       

 

c.      Using the principles of conformational analysis (angle, torsional and steric strain) evaluate the stability of the conformations drawn in (b) above and indicate which is the more stable.

 

                        Each conformation is free of angle strain (all are 109.5°).  Each is free of torsional strain (all bonds are staggered). The structure with the axial tert-butyl has two 1,3-diaxial interactions between hydrogen and tert-butyl for 22.4 kJ/mole of instability whereas that with axial methyl has two 1,3-diaxial interactions between hydrogen and methyl  for 7.6 kJ/mole of instability.

 

                        The more stable is therefore:

 

                       

 

d.      Derive an estimate for difference in stability between the most stable conformation of the cis and that of the trans isomer.

 

                   Trans has no angle, torsional, and steric strain.  The more stable cis has 2 methyl – hydrogen 1,3-diaxial interactions and therefore 7.6 kJ/mol of instability.

 

  1. Propose a synthesis of 2,2-dimethylbutane starting from alkanes having four or fewer carbons and any inorganic reagents.

 

           

           

  1. tert-Butyl peroxide is a source of free radicals:

 

(CH3)3CO-OC(CH3)3  ®  2(CH3)3CO.  (heat or light initiated)

 

A mixture of 2,3-dimethylbutane and tetrachloromethane, CCl4, is stable at 130°C.  If a small amount of tert-butyl peroxide is added, a reaction occurs that yields 2-chloro-2,3-dimethylbutane and trichloromethane.  A small amount of 2-methyl-2-propanol, (CH3)3COH, equivalent to the amount of peroxide used, is also formed.

 

a.      Draw the structure of 2-chloro-2,3-dimethylbutane.

 

                       

 

b.      Is this an example of a chain reaction?

 

                        Yes

 

c.      Which reactant provides the carbon in the CHCl3?

 

                        CCl4

 

d.      Propose a mechanism that explains the formation of the products.

 

 

e.      Draw the transition state for the initiation step.

 

                       

CHEM X6X Home Page | Faculté Saint-Jean | University of Alberta | Chemistry Department

This page is maintained by Dr. Ed Blackburn (Ed.Blackburn@UAlberta.CA), course instructor.

Updated May 18, 2006