Pima County Community College

OCHEM 1

Chapter 5 Stereochemistry At Tetrahedral Centers

SHORT ANSWER

Exhibit 5-1

For the following question(s) MATCH each definition to a term from the list below. Place the letter of the term in the blank to the left of the definition.

racemates                                                                            meso compounds

chirality center                                                                   optically active

chirality                                                                                 prochirality center

diastereomers                                                                   optically inactive

enantiomers                                                                       achiral

1)          describes organic molecules which rotate plane-polarized light.

2.     is the property of "handedness"; the property of an object that causes it to be nonsuperimposable on its mirror image.

3.     are stereoisomers that are not mirror images.

4.     is an atom in a molecule that is bonded to four different atoms or groups of atoms.

5.     are molecules which contain chirality centers and a plane of symmetry.

6.              describes an sp³-hybridized atom that can become a chirality center by changing one of its attached groups.

7. The specific rotation of a compound is denoted by the symbol:

R S

?

Exhibit 5-2

Place asterisks at all the chirality centers in each molecule below.

8.

9.

10.

11.

12.

13.

Exhibit 5-3

Assign R, S configurations to each indicated chirality center in the molecules below.

14. Refer to Exhibit 5-3. The configuration of this carbon atom (A) is             .

15. Refer to Exhibit 5-3. The configuration of this carbon atom (B) is              .

16. Refer to Exhibit 5-3. The configuration of this carbon atom (C) is              .

17. Refer to Exhibit 5-3. The configuration of this carbon atom (D) is             .

18. Refer to Exhibit 5-3. The configuration of this carbon atom (E) is              .

Exhibit 5-4

Consider the structure of streptimidone to answer the following question(s).

19. Refer to Exhibit 5-4. Assign R or S configuration to each chirality center indicated in streptimidone.

20. Refer to Exhibit 5-4. Based on the number of chirality centers, how many stereoisomers of streptimidone are possible?

21. Refer to Exhibit 5-4. Will streptimidone have a meso stereoisomer? Explain your answer.

Exhibit 5-5

Label each pair of stereoisomers below as:

enantiomers diastereomers identical

Place the letter of the correct answer in the blank to the left of the pair of stereoisomers.

22.                 

23.                 

24.                 

25.                 

26.                 

27.                 

28.                 

29. Draw a wedge-dash projection of (2R,3S)-dibromobutane.

30. Draw a Newman projection of the most stable conformation of (2R,3S)-dibromobutane sighting down the C2?C3 bond.

31. (2R,3S)-Dibromobutane is: optically active.

racemic. dextrorotatory.

a meso compound.

32. Estriol, a potent estrogenic hormone, has been isolated from the urine of pregnant women. When 40 mg of estriol is dissolved in 1.0 mL of dioxane and placed in a sample tube with 1 dm path length a rotation of +2.32? is observed. Calculate the specific rotation for estriol.

Exhibit 5-6

Refer to the structure below to answer the following question(s).

33. Refer to Exhibit 5-6. (S)-(?)-Serine: is dextrorotatory

rotates plane-polarized light in a counterclockwise direction rotates plane-polarized light in a clockwise direction

is racemic

34. Refer to Exhibit 5-6. Draw the enantiomer of (S)-(?)-serine in a wedge-dash projection.

35. Refer to Exhibit 5-6. Give the complete name of the enantiomer of (S)-(?)-serine.

Exhibit 5-7

A natural product having [?]_D = +40.3? has been isolated and purified.

36. Refer to Exhibit 5-7. This information indicates that the natural product: is racemic.

does not rotate plane-polarized light.

is levorotatory. is dextrorotatory.

37. Refer to Exhibit 5-7. Two structures have been proposed for this natural product. Circle the structure that is consistent with the information presented and briefly explain your choice.

Exhibit 5-8

Identify the indicated hydrogens in the following molecules as pro-R or pro-S.

Exhibit 5-9

Identify the indicated faces in the following molecules as re or si.

42. Acetoacetate synthase catalyzes the addition of pyruvate to ?-ketobutyrate to yield ?-aceto-?- hydroxybutyrate. If the addition occurs from the si face of ?-ketobutyrate, what is the stereochemistry of the product?

43. Explain why a work glove is chiral but disposable surgical gloves are not.

44. A white solid known to be enatiomerically pure is dissolved in water. This solution produced an observed optical rotation of +45.6°. The solution was allowed to stand and the optical rotation was measured repeatedly producing the data shown in the table.

Explain the pattern of observed rotation.

45. Lactic acid exists in two enantiomeric forms. In muscle tissue only (+)-lactic acid is found but in sour milk both (+)-lactic acid and (-)-lactic acid are present. Explain this observation.

46. Draw astructure for a singly substituted chiral chloroalkane with the that contains four carbon atoms. Indicate the chirality center with an asterisk (*).

MULTIPLE CHOICE

1.     Which of the following objects is not chiral?

1. baseball glove
2. ballerina
3. slipper corkscrew comb
4. All are chiral.

2. Which of the following would be has the highest priority according to the sequence rules?

1. —SH                                                                           
2. —CH₃
3. —NH₂                                                                        
4. —OH

3. Which of the following arranges the groups in order of decreasing priority according to the sequence rules?

CH₃ > CH₂CH₃ > CH₂OH > CO₂H                                  CH₂OH > CO₂H > CH₂CH₃ > CH₃ CH₃ > CH₂CH₃ > CO₂H >CH₂OH                                                                  CO₂H > CH₂OH > CH₂CH₃ > CH₃

4. 
   In which of the following groups can the carbon atom be a chiral center?

5. Which of the following compounds will rotate the plane of polarized light?

6. For which of the following generic substances is it not possible to isolate the enantiomers? (R₁, R₂ and R₃ represent different groups.)

1. It is possible to isolate the enantiomers of all of these.
2. It is not possible to isolate the enantiomers of any of these.

7. In muscles during strenuous exercise, under anaerobic conditions lactic acid builds up due to the following reaction.