Questions Relevant to Unit Test #4

2. (5 pts) Place asterisks(*) at all stereogenic centers in the molecule below.  3. (15 pts) The addition of HBr to optically active (R)-4-bromocyclohexene (I) gives four diastereomeric dibromocyclohexane products that were separated and characterized. a) (8 pts) Draw the four products including stereochemistry below.

b) (7 pts) Label each structure as chiral or achiral and below any achiral structure, indicate why it is achiral.

 5. (6 pts) Determine the configuration at the chiral centers in the structures below.

8. Label each pair of structures below as: A. enantiomers B. diastereomers

C. just identical D. identical meso compounds

Place the letter of your answer in the blank to next to the pair of stereoisomers. (6 pts)

a)________

b)________

 c)________ 9. (24 pts)Predict the major organic product(s) in each reaction below. If more than one major organic product is expected, draw each one. Be sure to indicate regiochemistry and stereochemistry, when relevant. (3 pts each)  


 
 
 

11. (4 pts) Explain why the following reaction fails.

12. (5 pts) Carbon-carbon bond forming reactions are important in organic synthesis. Starting with organic starting materials of 4 or fewer carbons, give a method for synthesis of:

(You need to show all reagents and stable intermediate structures.)
 

1. (6 pts) Draw structures corresponding to each of the following names. Either condensed or line structures may be used. Use wedge-dash projections to indicate stereochemistry.

    1. (S)-4-chlorocyclohexene

      2.  

       
       
       
       
       

    2. 4,4,5,5-tetramethyl-2-hexyne
2.    (6 pts)    Indicate whether the following structures are chiral or achiral.


 
 

3.    (6 pts) Assign R or S configuration to each indicated stereogenic center in the structure below. Place your answer in the appropriate box.

4. (3 pts) Draw the meso isomer of 2,5-dibromohexane.

5.    (16 pts) Consider the reaction below.
a) (4 pts) Assign appropriate R,S configuration to the chiral centers in the product II shown.

b) (2 pts) Are the products of the reactants shown expected to be optically active or optically inactive?

c) (4 pts) Considering the mechanism for this addition reaction and the stereochemistry of the product shown, draw the stereochemistry of the starting alkene for this reaction. (Remember that atoms connected by single bonds can rotate to different conformations.)
d) (3 pts) Draw the structure of the reactive intermediate formed in the two-step reaction leading to the product shown.
e) (3 pts) The answer given in part b requires that another structure be formed in this reaction. Draw its structure in the box labeled III and explain why it is formed.
6. Predict the major organic product(s) in each reaction below. Be sure to show stereochemistry when it is relevant.

d)

e)

7. (6 pts) For each reaction below, indicate the reagent necessary to produce the indicated product. a)


  9. (6 pts) For the following pairs of compounds indicate whether they are:

identical, enantiomers, diastereomers, or constitutional isomers.

a)

b)

c)

10.    (9 pts) Consider the reaction below.

  1. Although several structural isomers can be formed, one isomer is expected to predominate (be formed in largest amount). Draw the structure for this isomer.

    2.  

     
     
     
     
     
     
     
     
     
     
     
     

  2. Draw the reactive intermediate in this reaction that leads to the product drawn in part A. Is this structure chiral or achiral?

    3.  

     
     
     
     
     
     
     
     
     
     
     
     

  3. One of the minor products formed by reaction at a primary carbon is achiral. Draw the structure of this product and explain why it is achiral.

 
 
 
 
 
 


13.    (3 pts) The first step in the formation of a Grignard reagent from an alkyl halide is carried out in ether solvents. Why are polar solvents such as CH3OH not satisfactory as a solvent?

     
     
     
14.    (4 pts) Complete the wedge-dash representation for the Fischer projection shown:

15. (2 pts) Draw the enantiomer of the above structure.