ORGANIC CHEMISTRY 8Th Ed International Edition by John E. McMurry - Test Bank

ORGANIC CHEMISTRY 8Th Ed International Edition by John E. McMurry – Test Bank

 

Instant Download – Complete Test Bank With Answers

 

 

Sample Questions Are Posted Below

 

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.

 

a.	racemates	f.	meso compounds
b.	chirality center	g.	optically active
c.	chirality	h.	prochirality center
d.	diastereomers	i.	optically inactive
e.	enantiomers	j.	achiral

 

 

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

 

ANS:

g

 

 

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

 

ANS:

c

 

 

3. _____ are stereoisomers that are not mirror images.

 

ANS:

d

 

 

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

 

ANS:

b

 

 

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

 

ANS:

f

 

 

 

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

 

ANS:

h

 

 

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

 

a.	R
b.	S
c.	a
d.

 

 

ANS:

d

 

 

Exhibit 5-2

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

 

 

ANS:

 

 

 

 

ANS:

 

 

 

ANS:

 

 

 

 

 

ANS:

 

 

 

ANS:

 

 

 

 

 

ANS:

 

 

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 _____.

 

ANS:

R

 

 

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

 

ANS:

S

 

 

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

 

ANS:

R

 

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

 

ANS:

S

 

 

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

 

ANS:

S

 

 

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.

 

ANS:

 

 

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

 

ANS:

Streptimidone has two chirality centers so there are 2², or 4, possible stereoisomers.

 

 

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

 

ANS:

No. Meso compounds are compounds that contain chirality centers, but possess a plane of symmetry. Because the substituents on the chiral carbons are different in streptimidone it is impossible for any stereoisomer to have a plane of symmetry.

 

 

Exhibit 5-5

Label each pair of stereoisomers below as:

 

a.	enantiomers
b.	diastereomers
c.	identical

 

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

 

22. _____

 

ANS:

a

 

 

23. _____

 

ANS:

c

 

 

24. _____

 

ANS:

b

 

 

25. _____

 

ANS:

b

 

 

 

26. _____

 

ANS:

c

 

 

27. _____

 

ANS:

a

 

 

28. _____

 

ANS:

b

 

 

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

 

ANS:

 

 

 

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

 

ANS:

 

 

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

 

a.	optically active.
b.	racemic.
c.	dextrorotatory.
d.	a meso compound.

 

 

ANS:

d

 

 

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.

 

ANS:

 

 

Exhibit 5-6

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

 

 

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

 

a.	is dextrorotatory
b.	rotates plane-polarized light in a counterclockwise direction
c.	rotates plane-polarized light in a clockwise direction
d.	is racemic

 

 

ANS:

b

 

 

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

 

ANS:

 

 

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

 

ANS:

(R)-(+)-serine

 

 

Exhibit 5-7

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

 

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

 

a.	is racemic.
b.	does not rotate plane-polarized light.
c.	is levorotatory.
d.	is dextrorotatory.

 

 

ANS:

d

 

 

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.

 

 

ANS:

 

The information presented indicates that the natural product is optically active. To be optically active molecules must be chiral¾that is, they must not have a plane of symmetry. The cyclic structure, although is has chirality centers, has a plane of symmetry, indicated by the dashed line on the structure, and can, therefore, not be optically active. The circled structure has four chirality centers, and is not symmetric. We would expect it to be optically active.

 

 

Exhibit 5-8

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

 

 

ANS:

 

 

 

ANS:

 

 

 

Exhibit 5-9

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

 

 

ANS:

 

 

 

ANS:

 

 

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

 

 

ANS:

Addition of the aceto group to the si face results in the S enantiomer of a-aceto-a-hydroxybutyrate.

 

 

 

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

 

ANS:

Surgical gloves are not made to wear on a left hand or right hand but can be worn on either hand with an equally good fit.  This type of glove is symmetrical with respect to the positioning of the covering that goes on the thumb  –  it has a plane of symmetry.

OR

Work gloves have “front” and “back” sides.  The thumb is positioned differently with respect to the digits.  Surgical gloves have five symmetrical digits.  They do not have “front” and “back” sides.

 

 

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.

 

Time (min)	Observed Rotation (°)
10	+39.9
20	+5.6
30	-1.2
40	-23.4
40	-23.4

 

Explain the pattern of observed rotation.

 

ANS:

Some type of reaction, possibly a hydrolysis,  is occurring and the optically active dextrorotatory compound is being converted to the levorotatory enantiomer.

 

The change may be due to the production of a new compound with a specific rotation of -23.4°.  This might be verified by using this value to identify the compound if enough other informtion is know.

 

Assuming an equilibrium is established, an alternate explanation could be that it appears from the final value of the observed rotation that an equilibrium mixture of the two forms and that the levorotatory from predominates in the mixture.

 

 

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.

 

ANS:

Short answer:   Some type of stereoselectivity occurs in muscles that does not occur in milk.

 

Longer Answer:  The production of lactic acid in muscle tissue is catalyzed by biological catalysts or enzymes.  Enzymes are stereospecific in the substrates (reactants) upon which they can act as well as in the products they produce. Additionally, the substrates in such biological reactions also are only one of the two enantiomers. The souring of milk is a “purely chemical” process that is not stereoselective.

 

 

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

 

ANS:

 

The chirality center is indicated by the asterisk (*),

 

 

MULTIPLE CHOICE

 

1. Which of the following objects is not chiral?

a.	baseball glove
b.	ballerina slipper
c.	corkscrew
d.	comb
e.	All are chiral.

 

 

ANS: D

 

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

a.	—SH	c.	—CH3
b.	—NH2	d.	—OH

 

 

ANS: A

 

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

a.	CH3 > CH2CH3 > CH2OH > CO2H	c.	CH2OH > CO2H > CH2CH3 > CH3
b.	CH3 > CH2CH3 > CO2H >CH2OH	d.	CO2H > CH2OH > CH2CH3 > CH3

 

 

ANS: D

 

 

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

a.
b.
c.
d.
e.	The carbon atoms cannot be a chiral center in any of these groups.

 

 

ANS: E

 

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

a.		c.
b.		d.

 

 

ANS: C

 

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

a.
b.
c.
d.	It is possible to isolate the enantiomers of all of these.
e.	It is not possible to isolate the enantiomers of any of these.

 

 

ANS: A

 

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

 

 

The carbon atom indicated by the asterisk is

a.	chiral	c.	prochiral
b.	achiral	d.	both achiral and prochiral

 

 

ANS: D

 

8. A compound with [a]_D = +35.4° reacts to form a single product. The product of the reaction shows no optical activity.  This could mean that the product is:

a.	a racemate.
b.	does not have any chiral centers.
c.	is a meso compound.
d.	Any of the above are possible explanations.

 

 

ANS: D