chapter 4

Organic Chemistry, 7e (Bruice) Chapter 4 Isomers: The Arrangement of Atoms in Space 1) What type of isomers are CH3CH2OCH3 and CH3CH2CH2OH? A) constitutional B) symmetrical C) configurational D) conformational E) stereochemical Answer: A Section: 4-1 2) What is the relationship between the following compounds? A) configurational isomers B) conformational isomers C) constitutional isomers D) structural isomers E) positional isomers Answer: A Section: 4-1 3) What is the relationship between the following compounds? A) constitutional isomers B) enantiomers C) diastereomers D) conformational isomers E) superimposable without bond rotation Answer: A Section: 4-1 4) What is the relationship between the structures shown below? A) not isomers B) constitutional isomers C) conformational isomers D) configurational isomers E) enantiomers Answer: B Section: 4-1 5) What is the relationship between the structures shown below? A) diastereomers B) constitutional isomers C) conformational isomers D) configurational isomers E) enantiomers Answer: B Section: 4-1 6) Identify the pair of compounds. A) identical B) conformation isomers C) constitutional isomers D) configurational isomers E) none of the above Answer: D Section: 4-1 7) Which of the following cannot exhibit chirality? A) 2, 3-dibromobutane B) 1, 3-dibromobutane C) 1, 2-dichlorobutane D) 1, 4-dibromobutane E) 1-bromo-2-chlorobutane Answer: D Section: 4-2 8) Which of the following compounds is chiral? A) B) C) D) E) Answer: B Section: 4-2 9) Is the molecule shown below chiral or achiral? Answer: achiral Section: 4-2 10) Is the molecule shown below chiral or achiral? Answer: chiral Section: 4-2 11) Is the molecule shown below chiral or achiral? Answer: achiral Section: 4-2 12) Is the molecule shown below chiral or achiral? Answer: achiral Section: 4-2 13) Identify the compounds that are not chiral. Answer: A, B, and D Section: 4-2 14) Which of the following compounds has an asymmetric center? A) I B) II C) III D) IV E) V Answer: C Section: 4-3 15) How many asymmetric centers are present in a molecule of 2,4,6-trimethylheptane? A) 0 B) 1 C) 2 D) 3 E) 4 Answer: A Section: 4-3 16) How many asymmetric centers are present in the compound shown below? A) 1 B) 2 C) 3 D) 4 E) 5 Answer: C Section: 4-3 17) How many asymmetric centers are present in the compound below? Answer: 5 Section: 4-3 18) Identify the pair of compounds. A) identical B) conformational isomers C) constitutional isomers D) configurational isomers E) none of the above Answer: D Section: 4-3 19) Give the number of asymmetric centers in limonene. A) 2 B) 3 C) 1 D) 5 E) 4 Answer: C Section: 4-3 20) Identify the compound(s) with asymmetric centers. A) B) C) D) E) Answer: C Section: 4-3 21) A and B are stereoisomers. They are nonsuperimposable and are mirror images of one another. Which of the following best describes the relationship between A and B? A) structural isomers B) enantiomers C) conformational isomers D) diastereomers E) constitutional isomers Answer: B Section: 4-4 22) What is the relationship between the structures shown below? A) enantiomers B) diastereomers C) configurational isomers D) identical compounds E) constitutional isomers Answer: D Section: 4-4 23) Which of the following compounds is an enantiomer of the structure below? A) B) C) D) A and B E) It does not have an enantiomer. Answer: E Section: 4-4 24) Which of the following statements correctly describes the molecule shown below? A) It is achiral. B) It is meso. C) Its asymmetric center possesses the R configuration. D) The mirror image of this molecule is its enantiomer. E) The molecule possesses enantiotopic hydrogens. Answer: D Section: 4-4 25) Choose the enantiomer of the compound below. A) B) C) D) E) Answer: E Section: 4-4 26) Which of the following terms best describes the pair of compounds shown: enantiomers, diastereomers, or the same compound? Answer: the same compound Section: 4-4 27) The compound CH3CHClCH2CH=CHCH2CH3 contains only one asymmetric center. Explain why it has four stereoisomers. Answer: In addition to the single asymmetric center which may be either R or S, it also contains a carbon-carbon double bond which may be either E or Z. Thus, the four stereoisomers can be designated E, R; E, S; Z, R; and Z, S. Section: 4-5 28) Draw the enantiomer of the compound below. Answer: Section: 4-6 29) Identify the following compounds as R or S. A) S, S, R B) S, R, S C) R, S, S D) S, S, S E) R, R, R Answer: D Section: 4-6 30) Identify all pairs of enantiomers. A) B and D, A and C B) A and C C) B and D D) A and B, A and D, B and C, C and D E) B and D, A and B, A and D, B and C, C and D Answer: C Section: 4-6 31) Identify all identical compounds. A) B and D, A and C B) A and C C) B and D D) A and B, A and D, B and C, C and D E) B and D, A and B, A and D, B and C, C and D Answer: B Section: 4-6 32) Which of the following compounds has an S configuration? A) B) C) D) E) Answer: B Section: 4-7 33) Which of the following compounds has an R configuration? A) B) C) D) E) Answer: A Section: 4-7 34) Which of the following groups has the highest priority using the Cahn, Ingold, Prelog rules? A) B) C) OH D) OCH3 E) Answer: D Section: 4-7 35) The configuration of R-(+)-glyceraldehyde is as follows: What is the absolute configuration of (-)-lactic acid? A) R configuration B) L configuration C) S configuration D) R and S configuration E) D and L configuration Answer: A Section: 4-7 36) Indicate whether each of the following structures has the R or S configuration. What is the relationship between the two structures? Answer: Therefore, the two compounds are enantiomers. Section: 4-7 37) Label each asymmetric center in the compound below as R or S. Answer: Section: 4-7 38) Draw the structure of (S)-1-bromo-1-chloropropane. Take particular care to indicate three-dimensional stereochemistry detail properly. Answer: Section: 4-7 39) Provide the structure of (R)-4-octanol. Be careful to indicate proper stereochemistry. Answer: Section: 4-7 40) Identify the following compounds as R or S. A) R, S, R B) S, R, R C) S, S, S D) R, R, R E) S, S, R Answer: A Section: 4-7 41) Provide a careful structure for (2R,3S)-2,3-dibromohexane. Answer: Section: 4-7 42) Provide a careful structure for (2S,3S)-2,3-dibromohexane. Answer: Section: 4-7 43) Provide a careful structure for (2S,3R)-2,3-dibromohexane. Answer: Section: 4-7 44) Label each asymmetric center as R or S. Answer: Section: 4-7 45) Provide a careful structure for (2R,3S,4S)-2-bromo-4-methyl-3-hexanol. Answer: Section: 4-7 46) Provide a careful structure for (2S,3R,4R)-2-bromo-4-methyl-3-hexanol. Answer: Section: 4-7 47) Which of the following is a true statement? A) All chiral molecules possess a plane of symmetry. B) All achiral molecules are meso. C) All molecules which possess a single chirality center of the S configuration are levorotatory. D) A mixture of achiral compounds will be optically inactive. E) All molecules which possess two or more chirality centers will be chiral. Answer: D Section: 4-8 48) Which of the following is not true of enantiomers? A) They have the same melting point. B) They have the same boiling point. C) They have the same chemical reactivity with non-chiral reagents. D) They have the same density. E) They have the same specific rotation. Answer: E Section: 4-9 49) Which of the following is/are optically inactive? A) a 50-50 mixture of R and S enantiomers B) a meso compound C) every achiral compound D) a racemic mixture E) all the above Answer: E Section: 4-9 50) 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) They have different melting points. E) They have the same melting point, but they have different boiling points. Answer: A Section: 4-9 51) If (S)-glyceraldehyde has a specific rotation of -8.7, what is the specific rotation of (R)-glyceraldehyde? A) -8.7 B) +8.7 C) 0.0 D) cannot be determined from the information given Answer: B Section: 4-9 52) 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 Section: 4-9 53) A solution containing 0.96 g of 2-bromooctane in 10 mL ether solution gave an observed rotation of -1.8 in a 10 cm cell at
Calculate the specific rotation of this solution. Answer: [?] = [?] = = -18.75° in ether Section: 4-9 54) 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 Section: 4-9 55) Twenty grams of a compound was dissolved in 100 mL of solvent and gave an observed rotation of -20 degrees. The sample tube is 4 dm long. Calculate the specific rotation. Answer: -25 Section: 4-9 56) The specific rotation of a pure substance is 1.68. What is the specific rotation of a mixture containing 75% of this isomer and 25% of the (-) isomer? A) +1.68 B) 0 C) +1.26 D) +0.84 E) +.042 Answer: D Section: 4-10 57) The specific rotation of a pure substance is -5.90. What is the percentage of this isomer in a mixture with an observed specific rotation of -2.95? A) 25% B) 50% C) 75% D) 80% E) 0% Answer: C Section: 4-10 58) (-)-Mandelic acid has a specific rotation of -158. What would be the specific rotation of a solution which contains 40% (-)-mandelic acid and 60% (+)-mandelic acid? A) +95 B) +63 C) +32 D) -32 E) -63 Answer: C Section: 4-10 59) The specific rotation of (R)-(+)-glyceraldehyde is +8.7. If a mixture of glyceraldehydes enantiomers is 80% S and 20% R, what is the specific rotation of the mixture? Answer: -5.2 Section: 4-10 60) A sample of (+) and (-)-3-chlorohexane has a rotation of -20 degrees. Pure (+) -3-chlorohexane has a rotation of +40 degrees. Calculate the enantiomeric excess and the amount of (-) and (+)-3-chlorohexane in the original sample. Answer: 50%, 75% (-), 25% (+) Section: 4-10 61) What is the relationship between the following compounds? A) superimposable without bond rotation B) constitutional isomers C) conformational isomers D) diastereomers E) enantiomers Answer: E Section: 4-11 62) What is the relationship between the structures shown below? A) enantiomers B) diastereomers C) configurational isomers D) identical compounds E) constitutional isomers Answer: B Section: 4-11 63) What is the relationship between the following compounds? A) enantiomers B) diastereomers C) constitutional isomers D) conformational isomers E) identical compounds Answer: A Section: 4-11 64) What is the relationship between the following compounds? A) enantiomers B) diastereomers C) constitutional isomers D) conformational isomers E) identical compounds Answer: B Section: 4-11 65) Which of the following is chiral? A) cis-1-bromo-3-chlorocyclobutane B) trans-1-bromo-3-chlorocyclobutane C) cis-1,4-dimethylcyclohexane D) cis-1,3-dimethylcyclohexane E) trans-1,3-dimethylcyclohexane Answer: E Section: 4-11 66) How many diastereomers exist for the compound below? A) 2 B) 4 C) 6 D) 7 E) 8 Answer: C Section: 4-11 67) Which of the following terms best describes the pair of compounds shown: enantiomers, diastereomers, or the same compound? Answer: enantiomers Section: 4-11 68) Which of the following terms best describes the pair of compounds shown: enantiomers, diastereomers, or the same compound? Answer: diastereomers Section: 4-11 69) Which of the following terms best describes the pair of compounds shown: enantiomers, diastereomers, or the same compound? Answer: diastereomers Section: 4-11 70) Draw the structure of (2R,3S)-dichloropentane. Take particular care to indicate three-dimensional stereochemistry detail properly. Answer: Section: 4-11 71) Draw the structure of (2S,3R)-dichloropentane. Take particular care to indicate three-dimensional stereochemistry detail properly. Answer: Section: 4-11 72) Draw the structure of any diastereomer of (2R,3S)-dichloropentane. Take particular care to indicate three-dimensional stereochemistry detail properly. Answer: Section: 4-11 73) Steroisomers which are not mirror image isomers are ________. Answer: diastereomers Section: 4-11 74) Which of the following terms best describes the pair of compounds shown: enantiomers, diastereomers, or the same compound? Answer: the same compound Section: 4-11 75) Which of the following terms best describes the pair of compounds shown: enantiomers, diastereomers, or the same compound? Answer: the same compound Section: 4-11 76) Which of the following terms best describes the pair of compounds shown: enantiomers, diastereomers, or the same compound? Answer: enantiomers Section: 4-11 77) Draw the stereoisomers of 1,3-dichlorocyclopentane. Answer: Section: 4-11 78) Provide a perspective drawing of (2R,3S)-1,2,3-trichloropentane. Answer: Section: 4-11 79) Provide a perspective drawing of the enantiomer of (2R,3S)-1,2,3-trichloropentane. Answer: Section: 4-11 80) Provide a perspective drawing of each diastereomer of (2R,3S)-1,2,3-trichloropentane. Answer: Section: 4-11 81) Identify all pairs of diastereomers. A) B and D, A and C B) A and C C) B and D D) A and B, A and D, B and C, C and D E) B and D, A and B, A and D, B and C, C and D Answer: D Section: 4-11 82) Identify all meso compounds. A) B and D, A and C B) A and C C) B and D D) A and B, A and D, B and C, C and D E) B and D, A and B, A and D, B and C, C and D Answer: B Section: 4-11 83) Identify all configurational isomers. A) B and D, A and C B) A and C C) B and D D) A and B, A and D, B and C, C and D E) B and D, A and B, A and D, B and C, C and D Answer: E Section: 4-11 84) Which of the following is a meso compound? A) B) C) D) E) Answer: A Section: 4-13 85) What is the relationship between the following compounds? A) enantiomers B) diastereomers C) constitutional isomers D) conformational isomers E) identical compounds Answer: E Section: 4-13 86) Which of the following is a meso compound? A) trans-1, 4-dimethylcyclohexane B) cis-1, 3-dimethylcyclohexane C) trans-1, 3-dimethylcyclohexane D) cis-1, 4-dimethylcyclohexane E) trans-1, 2-dimethylcyclohexane Answer: B Section: 4-13 87) How many stereoisomers exist with the following basic connectivity? BrCH2CH(CH3)CH2CH3 A) 0 B) 1 C) 2 D) 4 E) 8 Answer: C Section: 4-13 88) How many stereoisomers exist with the following basic connectivity? CH3CHClCH2CHClCH3 A) 0 B) 1 C) 2 D) 3 E) 4 Answer: D Section: 4-13 89) 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 Section: 4-13 90) Consider the molecules with molecular formula C2H2Br2Cl2. a) Draw a structure that is optically inactive because it does not have an asymmetric center. b) Draw a structure that is optically inactive because it is a meso compound. c) Draw a structure that is optically active because it is chiral. Answer: a) no chirality center b) meso compound c) chiral Section: 4-13 91) Draw the structure of a meso form of 1,3-dichlorocyclopentane. Take particular care to indicate three-dimensional stereochemistry detail properly. Answer: Section: 4-13 92) Label the molecule shown as chiral or achiral. Answer: Achiral Section: 4-13 93) Label the molecule shown as chiral or achiral. Answer: Chiral Section: 4-13 94) Label the molecule shown as chiral or achiral. Answer: Achiral Section: 4-13 95) Label the molecule shown as chiral or achiral. Answer: Chiral Section: 4-13 96) Is the molecule shown chiral? Is it a meso compound? Answer: not chiral; not meso Section: 4-13 97) Is the molecule shown chiral? Is it a meso compound? Answer: not chiral; not meso Section: 4-13 98) Is the molecule shown chiral? Is it a meso compound? Answer: not chiral, meso Section: 4-13 99) Is the molecule shown chiral? Is it a meso compound? Answer: not chiral; not meso Section: 4-13 100) What is the configuration of the following compound? A) 2S, 3R B) 3R, 3S C) 2S, 3S D) 2R, 3R E) Can't do R and S; the compound is achiral. Answer: C Section: 4-14 101) In the Fischer projection below, what are the configurations of the two asymmetric centers? A) 2R, 3R B) 2R, 3S C) 2S, 3R D) 2S, 3S E) cannot be determined from structure Answer: A Section: 4-14 102) Label each asymmetrical carbon in the compound below as R or S. Answer: Section: 4-14 103) Draw a perspective formula of (2R,3S)-3-bromo-2-butanol. Answer: Section: 4-14 104) Draw any diastereomer of (2R,3R)-2,3-dichloropentane. Be careful to indicate proper stereochemistry. Answer: Section: 4-14 105) Can one predict whether a compound with a single asymmetric center is dextro- or levorotatory based on the R/S assignment at this asymmetric center? 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. Section: 4-14 106) Assign an R or S configurational label to each asymmetric center in the molecule below. Answer: Section: 4-14 107) Give the complete name(s) of the following compound. Answer: (2R, 4S)-2,4-dichloropentane or (2S, 4R)-2,4-dichloropentane Section: 4-14 108) 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 or chromatographic separation using a chiral stationary phase. Section: 4-15 109) The compound below contains an asymmetric center at nitrogen. Why can't individual stereoisomers of this compound be isolated at room temperature? Answer: Nitrogen has a pair of nonbonding electrons that allow it to turn "inside out" at room temperature. Because of rapid inversion, the individual stereoisomers cannot be isolated. Section: 4-16 110) Identify the compounds that have an asymmetric center. A) A B) B C) C D) A and B E) A, B, and C Answer: E Section: 4-16 111) Identify the pair of compounds. A) identical B) conformational isomers C) constitutional isomers D) configurational isomers E) none of the above Answer: C Section: 4-98 1 Copyright 2014 Education, Inc.