Organic Chemistry Wade Test bank

Organic Chemistry, 7e (Wade) Chapter 5 Stereochemistry 1) What term describes the structural relationship between cis-1,2-dimethylcyclopentane and trans-1,3-dimethylcyclopentane? A) not isomers B) constitutional isomers C) enantiomers D) diastereomers E) conformers Answer: B Diff: 2 Section: 5.1 2) What term describes the structural relationship between (2R,3R,4S)-2,3,4-trichloroheptane and (2S,3S,5R)-2,3,5-trichloroheptane? A) not isomers B) constitutional isomers C) enantiomers D) diastereomers E) conformers Answer: B Diff: 2 Section: 5.1 3) What is the structural relationship between the two molecule shown below?

A) constitutional isomers B) enantiomers C) diastereomers D) conformational isomers E) not isomers Answer: A Diff: 2 Section: 5.1

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4) __________ are isomers which have the same bonding sequence but differ in the orientation of their atoms in space. Answer: Stereoisomers Diff: 1 Section: 5.1 5) How many asymmetric carbon atoms are present in the following compound?

A) 0 B) 1 C) 2 D) 3 E) 4 Answer: B Diff: 1 Section: 5.2 6) How many asymmetric carbon atoms are present in the following compound?

A) 0 B) 1 C) 2 D) 3 E) 4 Answer: A Diff: 1 Section: 5.2

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7) How many enantiomers are there of the molecule shown below?

A) 0 B) 1 C) 2 D) 3 E) 6 Answer: B Diff: 1 Section: 5.2 8) Which of the following incorrectly describes cis-1,2-dimethylcyclopentane? A) It is a meso compound. B) It is achiral. C) It contains two asymmetric carbons. D) Its diastereomer is trans-1,2-dimethylcyclopentane. E) It has an enantiomer. Answer: E Diff: 1 Section: 5.2 9) Which of the statements below correctly describes an achiral molecule? A) The molecule has a nonsuperimposable mirror image. B) The molecule exhibits optical activity when it interacts with plane-polarized light. C) The molecule has an enantiomer. D) The molecule might be a meso form. E) None of the above Answer: D Diff: 2 Section: 5.2

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10) What term describes the structural relationship between (2R,3R,4S)-2,3,4-trichloroheptane and (2S,3S,4R)-2,3,4-trichloroheptane? A) not isomers B) constitutional isomers C) enantiomers D) diastereomers E) conformers Answer: C Diff: 2 Section: 5.2 11) If possible, draw the structure of the enantiomer of the molecule shown below.

Answer:

Diff: 2 Section: 5.2 12) Is the mirror image of the following molecule an enantiomer or is it superimposable with it?

Answer: Superimposable. The molecule is achiral. Diff: 2 Section: 5.2

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13) Circle each chiral molecule among those shown below.

Answer:

Diff: 2 Section: 5.2 14) Circle each chiral molecule among those shown below.

Answer:

Diff: 2 Section: 5.2

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15) Draw the enantiomer of the molecule shown below.

Answer:

Diff: 2 Section: 5.2 16) Circle all structures shown below that are chiral.

Answer:

Diff: 3 Section: 5.2 17) Is the molecule shown below chiral or achiral? (CH3)3CCH(CH3)2 Answer: achiral Diff: 1 Section: 5.2

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18) Which of the following terms best describes the pair of compounds shown: enantiomers, diastereomers, or the same compound?

Answer: the same compound Diff: 1 Section: 5.2 19) Which of the following terms best describes the pair of compounds shown: enantiomers, diastereomers, or the same compound?

Answer: the same compound Diff: 1 Section: 5.2 20) Which of the following terms best describes the pair of compounds shown: enantiomers, diastereomers, or the same compound?

Answer: enantiomers Diff: 1 Section: 5.2 21) How many asymmetric carbons are present in the compound below?

Answer: 1 Diff: 1 Section: 5.2

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22) How many asymmetric carbons are present in the compound below?

Answer: none Diff: 1 Section: 5.2 23) How many asymmetric carbons are present in the compound below?

Answer: 5 Diff: 1 Section: 5.2 24) Is the molecule shown below chiral or achiral? CH3CH2CH(CH3)CH2CH3 Answer: achiral Diff: 2 Section: 5.2 25) Is the molecule shown below chiral or achiral?

Answer: achiral Diff: 2 Section: 5.2 26) Is the molecule shown below chiral or achiral?

Answer: chiral Diff: 2 Section: 5.2

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27) Is the molecule shown below chiral or achiral?

Answer: achiral Diff: 2 Section: 5.2 28) Is the molecule shown below chiral or achiral?

Answer: achiral Diff: 2 Section: 5.2 29) Is the molecule shown below chiral or achiral?

Answer: chiral Diff: 2 Section: 5.2 30) Which of the following terms best describes the pair of compounds shown: enantiomers, diastereomers, or the same compound?

Answer: enantiomers Diff: 2 Section: 5.2

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31) How many asymmetric carbons are present in the compound below?

Answer: 2 Diff: 2 Section: 5.2 32) How many asymmetric carbons are present in the compound below? 3-ethyl-2,2,4-trimethylpentane Answer: 1 Diff: 2 Section: 5.2 33) Is the molecule shown below chiral or achiral?

Answer: achiral Diff: 3 Section: 5.2 34) Is the molecule shown below chiral or achiral?

Answer: achiral Diff: 3 Section: 5.2 35) Is the molecule shown below chiral or achiral?

Answer: achiral Diff: 3 Section: 5.2

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36) Which of the following terms best describes the pair of compounds shown: enantiomers, diastereomers, or the same compound?

Answer: enantiomers Diff: 3 Section: 5.2 37) How many asymmetric carbons are present in the compound below?

Answer: 5 Diff: 3 Section: 5.2 38) Does the molecule shown below contain asymmetric carbon atoms? Is this molecule chiral?

Answer: Yes, the molecule contains 4 asymmetric carbon atoms. No, the molecule is not chiral since it is superimposable with its mirror image. Diff: 3 Section: 5.2

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39) Which of the following configurations corresponds to the structure below?

A) (4R, 5R) B) (4R, 5S) C) (4S, 5R) D) (4S, 5S) Answer: A Diff: 3 Section: 5.3 40) Label each asymmetric carbon in the molecule below as having the R or S configuration.

Answer:

Diff: 2 Section: 5.3 41) Assign the proper configurational label, R or S, to the chiral carbon in the molecule shown below.

Answer: S Diff: 2 Section: 5.3

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42) Assign the proper configurational label, R or S, to each chiral carbon in the molecule below.

Answer:

Diff: 2 Section: 5.3 43) For the structure shown below, draw the stereoisomer having a configuration of (1R,3S,4S) in a perspective structure.

Answer:

Diff: 3 Section: 5.3

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44) Captopril is used to treat high blood pressure and congestive heart failure. Label the chiral centers as R or S.

Answer:

Diff: 3 Section: 5.3 45) Label each asymmetric carbon in the compound below as R or S.

Answer:

Diff: 1 Section: 5.3 46) Draw the structure of (S)-1-bromo-1-chloropropane. Take particular care to indicate threedimensional stereochemical detail properly. Answer:

Diff: 1 Section: 5.3 47) Draw the structure of (S)-2-bromobutane. Take particular care to indicate stereochemistry properly. Answer:

Diff: 1 Section: 5.3

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48) Label each asymmetric carbon in the compound below as R or S.

Answer:

Diff: 2 Section: 5.3 49) Label each asymmetric carbon in the compound below as R or S.

Answer:

Diff: 2 Section: 5.3 50) Draw the structure of (2R,3S)-2,3-dichloropentane. Take particular care to indicate threedimensional stereochemical detail properly. Answer:

Diff: 2 Section: 5.3 51) Draw the structure of the enantiomer of (2S, 3R)-2,3-dichloropentane. Take particular care to indicate three-dimensional stereochemical detail properly. Answer:

Diff: 2 Section: 5.3 15

52) Draw the structure of any diastereomer of (2S, 3R)-2,3-dichloropentane. Take particular care to indicate three-dimensional stereochemical detail properly. Answer:

Diff: 2 Section: 5.3 53) Draw the structure of (1R, 2R)-1-bromo-2-chlorocyclobutane. Take particular care to indicate stereochemistry properly. Answer:

Diff: 2 Section: 5.3 54) Draw the structure of (S)-3-chloro-3-methylhexane. Take particular care to indicate stereochemistry properly. Answer: Diff: 2 Section: 5.3 55) Draw the structure of (1R, 2S, 3S)-1,2-dibromo-3-ethylcyclohexane. Take particular care to indicate stereochemistry properly. Answer:

Diff: 2 Section: 5.3

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56) Label each asymmetric carbon in the compound below as R or S.

Answer:

Diff: 3 Section: 5.3 57) Label each assymetric carbon in the compound below as R or S.

Answer:

Diff: 3 Section: 5.3 58) Which of the following statements correctly pertains to a pair of enantiomers? A) They rotate the plane of polarized light by exactly the same amount and in opposite directions. B) They rotate the plane of polarized light by differing amounts and in opposite directions. C) They rotate the plane of polarized light by differing amounts and in the same direction. D) The have different melting points. E) They have the same melting point, but they have different boiling points. Answer: A Diff: 2 Section: 5.4

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59) If (S)-glyceraldehyde has a specific rotation of -8.7°, what is the specific rotation of (R)glyceraldehyde? A) 0.0° B) -8.7° C) +8.7° D) cannot be determined from the information given Answer: C Diff: 2 Section: 5.4 60) Which of the following statements is (are) true for the compound (R)-2-butanol? A) This compound is chiral. B) This compound is optically active. C) This compound has an enantiomer. D) all of the above E) none of the above Answer: D Diff: 2 Section: 5.4 61) Predict the specific rotation of the compound shown.

A) It is impossible to predict; must be determined experimentally. B) Because both asymmetric centers are R, the compound is dextrorotatory. C) Because both asymmetric centers are S, the compound is levorotatory. D) Zero; the compound is achiral. E) Because this compound represents a racemic mixture, the compound is dextrorotatory. Answer: D Diff: 2 Section: 5.4

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62) A student measured the optical activity of an unknown sugar at two different concentrations. The results of his measurements are shown below. Given that the sample cell had a path length of 10.0 cm, calculate the specific rotation for the unknown sugar. (Hint: consider each measurement of plane polarized light has a true reading and a "ghost" reading 180° from the true reading). concentration 2.00 g sugar in 10.0 mL water 5.00 g sugar in 10.0 mL water

observed rotation +159.1° +127.8°

A) -10.5° B) +25.6° C) +79.5° D) -105° E) +256° Answer: D Diff: 3 Section: 5.4 63) Compounds that rotate the plane of polarized light clockwise are called __________. Answer: dextrorotatory Diff: 1 Section: 5.4 64) Would a 50:50 mixture of (2R,3R)-2,3-dibromobutane and (2R,3S)-2,3-dibromobutane be optically active? Explain. Answer: Yes, the mixture would be optically active. This is not a racemic mixture but a mixture of diastereomers. The specific rotations of diastereomers are not the same in magnitude nor necessarily opposite in sign. Diff: 2 Section: 5.4 65) Can one predict whether a compound with a single asymmetric carbon is dextro- or levorotatory based on the R/S assignment at this asymmetric carbon? Explain briefly. Answer: No. R/S assignment is purely a convention of nomenclature and is completely independent of the direction in which plane-polarized light is rotated by the compound. Diff: 2 Section: 5.4 66) A newly isolated natural product was shown to be optically active. If a solution of 2.0 g in 10 mL of ethanol in a 50 cm tube gives a rotation of +2.57°, what is the specific rotation of this natural product? Answer: +2.57° Diff: 3 Section: 5.4

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67) A mixture of equal amounts of two enantiomers __________. A) is called a racemic mixture B) is optically inactive C) implies that the enantiomers are meso forms D) both A and B E) none of the above Answer: D Diff: 2 Section: 5.6 68) If a mixture contains 75% of one compound and 25% of its enantiomer, what is the e.e. of the mixture? A) 100 B) 75 C) 50 D) 25 E) 3 Answer: C Diff: 2 Section: 5.7 69) A mixture of two enantiomers with a composition of 65.0% R has an observed rotation of -25.3° in a 10.0 cm polarimeter tube. If the mixture has a concentration of 2.038 g/mL at 25°C, what is the predicted [α]25D of an optically pure sample of the S enantiomer? A) -25.3° B) -53.5° C) +12.4° D) +41.3° E) +53.5° Answer: D Diff: 3 Section: 5.7 70) Calculate the e.e. of a mixture containing 8.0 g of (-)-glyceraldehyde and 2.0 g of (+)-glyceraldehyde. Answer: 60% Diff: 2 Section: 5.7 71) The specific rotation of pure (-)-2-butanol is -13.5°. What % of a mixture of the two enantiomeric forms is the (+)-form if the specific rotation of this mixture is +7.0°? Answer: 76% Diff: 3 Section: 5.7

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72) (-)-Lactic acid has a specific rotation of -3.8°. What is the specific rotation of a solution containing 7.5 g of (-)-lactic acid and 2.5 g of (+)-lactic acid? Answer: -1.9° Diff: 3 Section: 5.7 73) Explain the stereochemical relationship, if any, among the following two structures and describe whether or not they could be theoretically isolated from each other. (Note: Some H atoms are omitted for clarity.)

Answer: These structures are conformationally dependent diastereomers. They could not be isolated because they are actually the same molecule. Diff: 3 Section: 5.8 74) Can a molecule be chiral if it contains no asymmetric carbons? Explain briefly. Answer: Yes. The presence of asymmetric carbons is not required for a molecule to be chiral. The only requirement is that the molecule be nonsuperimposable with its mirror image. Structural features other than asymmetric carbons can lead to chirality. Diff: 2 Section: 5.9 75) Which of the following terms best describes the pair of compounds shown: enantiomers, diastereomers, or the same compound?

Answer: enantiomers Diff: 3 Section: 5.9

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76) Why is the following structure not a meso compound?

Answer: The functional group at the top (aldehyde) is different from the bottom (alcohol) and thus there is no internal reflective plane in the molecule Diff: 1 Section: 5.10 77) Draw the Fischer projection of (2R,4R)-2,4-dibromopentane. Answer:

Diff: 2 Section: 5.10 78) Provide a Fischer projection of (2R,3R,4S)-2,3,4-trichloroheptane. Answer:

Diff: 3 Section: 5.10

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79) Provide a Fischer projection of (2S,3S,4S)-2,3,4-trichloroheptane. Answer:

Diff: 3 Section: 5.10 80) Draw the Fischer projection of (S)-2-hydroxybutanoic acid, CH3CH2CH(OH)COOH. Answer:

Diff: 1 Section: 5.10 81) How many diastereomers are there of the molecule shown below?

A) 0 B) 1 C) 2 D) 3 E) 6 Answer: C Diff: 1 Section: 5.11

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82) Which of the following terms best describes the stereochemical relationship of the two compounds shown below in Fischer notation?

A) enantiomers B) diastereomers C) constitutional isomers D) cis/trans - isomers E) meso - same structure Answer: B Diff: 2 Section: 5.11 83) Which of the following statements is (are) true for the compound (3R, 4R)-3,4dimethylhexane? A) This compound is chiral. B) The enantiomer of this compound is (3S, 4S)-3,4-dimethylhexane. C) This compound is a diastereomer of (3R, 4S)-3,4-dimethylhexane. D) all of the above E) none of the above Answer: D Diff: 2 Section: 5.11 84) Which of the following terms correctly describe(s) the structural relationship between cis1,3-dimethylcyclopentane and trans-1,3-dimethylcyclopentane? A) enantiomers B) diastereomers C) geometric isomers D) both A and C E) both B and C Answer: E Diff: 2 Section: 5.11

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85) What term describes the structural relationship between (E)- and (Z)-2-pentene? A) not isomers B) constitutional isomers C) enantiomers D) diastereomers E) conformers Answer: D Diff: 2 Section: 5.11 86) What term describes the structural relationship between cis-1,2-dimethylcyclopentane and trans-1,2-dimethylcyclopentane? A) not isomers B) constitutional isomers C) enantiomers D) diastereomers E) conformers Answer: D Diff: 2 Section: 5.11 87) What term describes the structural relationship between (2R,3R,4S)-2,3,4-trichloroheptane and (2R,3R,4R)-2,3,4-trichloroheptane? A) not isomers B) constitutional isomers C) enantiomers D) diastereomers E) conformers Answer: D Diff: 2 Section: 5.11

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88) How many diastereomers are there of the molecule shown below?

A) 0 B) 1 C) 2 D) 3 E) 6 Answer: E Diff: 3 Section: 5.11 Use the following three structures to answer the questions below.

89) The relationship between I and III is: A) same compound B) enantiomers C) diastereomers D) constitutional isomers Answer: C Diff: 3 Section: 5.11 90) The relationship between I and II is: A) same compound B) enantiomers C) diastereomers D) constitutional isomers Answer: C Diff: 3 Section: 5.11

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91) Which of the structures above are meso structures? A) I B) II C) III D) II & III E) None of the previous Answer: A Diff: 3 Section: 5.13 92) Stereoisomers which are not mirror image isomers are __________. Answer: diastereomers Diff: 1 Section: 5.11 93) If possible, draw the structure of any diastereomer of the molecule shown below.

Answer:

Diff: 2 Section: 5.11

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94) If possible, draw the structure of any diastereomer of the molecule shown below.

Answer:

Diff: 2 Section: 5.11 95) Draw any diastereomer of the molecule shown below.

Answer:

Diff: 2 Section: 5.11

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96) Which of the following terms best describes the pair of compounds shown: enantiomers, diastereomers, or the same compound?

Answer: diastereomers Diff: 2 Section: 5.11 97) Which of the following terms best describes the pair of compounds shown: enantiomers, diastereomers, or the same compound?

Answer: the same compound Diff: 2 Section: 5.11 98) Which of the following terms best describes the pair of compounds shown: enantiomers, diastereomers, or the same compound?

Answer: diastereomers Diff: 3 Section: 5.11 99) Which of the following terms best describes the pair of compounds shown: enantiomers, diastereomers, or the same compound?

Answer: the same compound Diff: 3 Section: 5.11

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100) Which of the following molecules, if isolated in its pure form, would demonstrate optical activity ?

A) both IV and V B) both I and III C) only II D) both III and IV E) both I and V Answer: A Diff: 3 Section: 5.12 101) Which of the following statements is (are) true for the compound cis-1,2dichlorocyclopropane? A) This compound is chiral. B) The enantiomer of this compound is trans-1,2-dichlorocyclopropane. C) This compound contains no asymmetric carbons. D) all of the above E) none of the above Answer: E Diff: 2 Section: 5.13

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102) How many enantiomers are there of the molecule shown below?

A) 0 B) 1 C) 2 D) 3 E) 6 Answer: A Diff: 2 Section: 5.13 103) If possible, draw the structure of the enantiomer of the molecule shown below.

Answer: The compound is an achiral, meso compound; it has no enantiomer. Diff: 2 Section: 5.13 104) Can the molecule shown below be properly described as a meso compound?

Answer: Yes Diff: 1 Section: 5.13

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105) Can the molecule shown below be properly described as a meso compound?

Answer: Yes Diff: 1 Section: 5.13 106) Draw the structure of the meso form of 1,3-dichlorocyclopentane. Take particular care to indicate three-dimensional stereochemical detail properly. Answer:

Diff: 2 Section: 5.13 107) Can the molecule shown below be properly described as a meso compound? (CH3)2CHCH2CH3 Answer: No Diff: 2 Section: 5.13 108) Can the molecule shown below be properly described as a meso compound?

Answer: No Diff: 2 Section: 5.13 109) Can the molecule shown below be properly described as a meso compound?

Answer: No Diff: 2 Section: 5.13

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110) Is it theoretically possible to separate the pair of compounds below by distillation? Explain briefly.

Answer: Yes. The molecules are related as diastereomers and hence have different boiling points. Diff: 2 Section: 5.15 111) The process by which enantiomers are separated is called __________. Answer: resolution Diff: 1 Section: 5.16 112) Can one separate a mixture of enantiomers by gas chromatography? Explain. Answer: Provided the compounds can be volatilized, a mixture of enantiomers can be separated by GC if an appropriate chiral column can be found. Enantiomers will be retained differently by the chiral stationary phase of the column. Diff: 3 Section: 5.16 113) Briefly describe how two enantiomers might be separated. Answer: The two compounds can be converted to diastereomers, separated based on different physical properties of these diastereomers, and subsequently returned to their original forms after separation. Another method involves the chromatographic separation using a chiral stationary phase. Diff: 2 Section: 5.16

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