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Chapter 7 Structure and Preparation of Alkenes - Elimination Reactions: Answers Prof. Jayaraman Sivaguru Chapter 7: Structure and Preparation of Alkenes – Elimination Reactions 1. Carbon-carbon double bonds do not freely rotate like carbon-carbon single bonds. Why? A) The double bond is much stronger and thus more difficult to rotate. B) Overlap of the two 2p orbitals of the π bond would be lost. C) The shorter bond length of the double bond makes it more difficult for the attached groups to pass each other. D) Overlap of the sp2 orbitals of the carbon-carbon σ bond would be lost. Ans: B 2. What is the IUPAC name of the following compound? A) 2,5-dimethyl-1-hexene B) 1,4-dimethyl-1-hexene Ans: A C) D) 2,5-dimethyl-2-hexene 2,5-dimethyl-5-hexene 3. What is the IUPAC name of the following compound? A) 2-methyl-3-propyl-2-pentene B) 3-ethyl-2-methyl-2-hexene Ans: B C) D) 4-ethyl-5-methyl-4-hexene 4-methyl-3-propyl-3-pentene 4. What is the IUPAC name of the following compound? A) 3-ethyl-8-methyl-3-nonene B) 7-ethyl-2-methyl-6-nonene Ans: A C) D) 1,1-diethyl-6-methyl-3-heptene 3-ethyl-7-isopropyl-3-octene 5. How many isomeric alkenes of formula C4H8, including stereoisomers, are possible? A) two B) three C) four D) five Ans: C Page 1 Chem 341: Organic Chemistry, Prof. Jayaraman Sivaguru, Fall 2016. Chapter 7 Structure and Preparation of Alkenes - Elimination Reactions: Answers Prof. Jayaraman Sivaguru 6. How many isomeric alkenes of formula C5H10, including stereoisomers, are possible? A) three B) four C) five D) six Ans: D 7. What is the IUPAC name of the following compound? A) 3-bromo-2-methylcyclohexene B) 1-bromo-2-methyl-2-cyclohexene Ans: C C) D) 6-bromo-1-methylcyclohexene 2-bromo-1-methylcyclohexene 8. What is the IUPAC name of the following compound? A) 3-ethyl-propyl-1-heptene B) ethyl-3-vinyloctane Ans: D C) D) 4,6-diethyl-1-octene 3,5-diethyl-1-octene 9. Which of the following alkenes exhibit E-Z isomerism? I. CH3CH2CH CHCH2CH3 II. (CH3)2C CHCH3 III. CH3CH2CH CHBr IV. H2C CHCH2CH(CH3)2 A) I and II Ans: B B) I and III C) II and IV D) I, II, and III 10. Which of the following alkenes exhibit E-Z isomerism? I. 1-chloropropene II. 2-chloropropene III. 3-chloropropene A) only I B) I and II C) II and III D) I and III Ans: A Page 2 Chem 341: Organic Chemistry, Prof. Jayaraman Sivaguru, Fall 2016. Chapter 7 Structure and Preparation of Alkenes - Elimination Reactions: Answers Prof. Jayaraman Sivaguru 11. What is the IUPAC name of the following compound? A) B) C) D) Ans: (E)-3-bromo-1-fluoro-2-methylpropene (Z)-3-bromo-1-fluoro-2-methylpropene (E)-1-bromo-3-fluoro-2-methylpropene (Z)-1-bromo-3-fluoro-2-methylpropene A 12. Which of the following C6H12 isomers has the highest heat of combustion? A) 1-hexene B) trans-3-hexene C) cis-3-hexene D) 2-methyl-2-pentene Ans: A 13. Identify the major organic product expected from the acid-catalyzed dehydration of 2methyl-2-pentanol. A) 2-methyl-1-pentene C) 3-methyl-1-pentene B) 2-methyl-2-pentene D) cis-3-methyl-2-pentene Ans: B 14. Which alcohol below would undergo acid-catalyzed dehydration most readily? A) A B) B Ans: D C) C D) D 15. What is the slow, rate-determining step, in the acid-catalyzed dehydration of 2-methyl2-propanol? A) B) C) D) Ans: Protonation of the alcohol to form an oxonium ion. Loss of water from the oxonium ion to form a carbocation. Loss of a β-hydrogen from the carbocation to form an alkene. The simultaneous loss of a β-hydrogen and water from the oxonium ion. B Page 3 Chem 341: Organic Chemistry, Prof. Jayaraman Sivaguru, Fall 2016. Chapter 7 Structure and Preparation of Alkenes - Elimination Reactions: Answers Prof. Jayaraman Sivaguru 16. Which of the following carbocations is(are) likely to undergo a rearrangement? A) only I Ans: D B) I and III C) II and III D) I, II, and III 17. Predict the major product of the following reaction. A) A B) B Ans: C C) C D) D 18. Which of the following expressions is the experimentally observed rate law for an E2 reaction of an alkyl halide? A) rate = k[RX] B) rate = k[RX][base] C) rate = k[RX]2 D) rate = k[base] Ans: B 19. Which of the following most readily undergoes an E2 reaction with sodium ethoxide (NaOCH2CH3)? A) (CH3)3CF B) (CH3)3CCl C) (CH3)3CBr D) (CH3)3CI Ans: D Page 4 Chem 341: Organic Chemistry, Prof. Jayaraman Sivaguru, Fall 2016. Chapter 7 Structure and Preparation of Alkenes - Elimination Reactions: Answers Prof. Jayaraman Sivaguru 20. How many isomeric alkenes are possible, including stereoisomers, in the following reaction? A) two B) three C) four Ans: B D) five 21. In the dehydrohalogenation of 2-bromobutane, which conformation below leads directly to the formation of cis-2-butene? A) only I Ans: A B) only II C) only III D) I and II 22. Which of the following cannot undergo an E2 reaction? A) only I Ans: A B) only II C) only III D) I and III 23. Which of the following would you predict to be the best method for doing the following conversion with the highest yield? A) H2SO4, heat B) NaOCH2CH3 Ans: D C) H3PO4 D) (1) PBr3 (2) KOC(CH3)3 Page 5 Chem 341: Organic Chemistry, Prof. Jayaraman Sivaguru, Fall 2016. Chapter 7 Structure and Preparation of Alkenes - Elimination Reactions: Answers Prof. Jayaraman Sivaguru 24. When a strong base is used in the elimination reaction of an alkyl halide the mechanism, in general, is A) E1. B) E2. C) E1 for tertiary halides, E2 for primary and secondary halides. D) E2 for tertiary halides, E1 for primary and secondary halides. Ans: B 25. Which of the following sets of conditions most favors the E1 mechanism? A) when the alkyl halide is tertiary and the base is a weak base B) when the alkyl halide is tertiary and the base is a strong base C) when the alkyl halide is primary or secondary and the base is a weak base D) when the alkyl halide is primary or secondary and the base is a strong base Ans: A 26. Which of the following would have the fastest rate of reaction to form 4-tertbutylcyclohexene? A) A B) B Ans: D C) C D) D Page 6 Chem 341: Organic Chemistry, Prof. Jayaraman Sivaguru, Fall 2016. Chapter 7 Structure and Preparation of Alkenes - Elimination Reactions: Answers Prof. Jayaraman Sivaguru 27. What is the first step in the mechanism of the dehydration reaction of a tertiary alcohol with sulfuric acid to form an alkene? A) the loss of OH– to form a carbocation B) the protonation of the hydroxyl group C) the loss of the proton from the hydroxyl group to give an alkoxide ion D) the removal of a β-hydrogen from the alcohol Ans: B 28. Which of the following does not give 1,2-dimethylcyclohexene as one of the acidcatalyzed dehydration products? A) A B) B Ans: D C) C D) D 29. Including E-Z isomers, how many E2 products are possible in the following reaction? A) one B) two Ans: C C) three D) four 30. Which of the following compounds gives a single E2 product on reaction with sodium ethoxide, NaOCH2CH3? A) I and II Ans: B B) I and III C) II and III D) I, II, and III Page 7 Chem 341: Organic Chemistry, Prof. Jayaraman Sivaguru, Fall 2016. Chapter 7 Structure and Preparation of Alkenes - Elimination Reactions: Answers Prof. Jayaraman Sivaguru 31. Which of the following will give 2-methyl-1-butene as the only alkene product on treatment with KOC(CH3)3 in dimethyl sulfoxide? A) 2-bromo-3-methylbutane C) 2-bromo-2-methylbutane B) 1-bromo-3-methylbutane D) 1-bromo-2-methylbutane Ans: D 32. If the following E2 reaction proceeds through an anti-periplanar transition state, what product or products are expected? CH3 KOC(CH3)3 (CH3)3COH A) B) C) D) Ans: Cl only 1-methylcyclohexene only 3-methylcyclohexene only 4-methylcyclohexene equal amounts of 1-methylcyclohexene and 3-methylcyclohexene B 33. Which of the following stereoisomers gives the exclusive E2 product shown? A) A B) B Ans: D C) C D) D Page 8 Chem 341: Organic Chemistry, Prof. Jayaraman Sivaguru, Fall 2016. Chapter 7 Structure and Preparation of Alkenes - Elimination Reactions: Answers Prof. Jayaraman Sivaguru 34. Zaitsev's rule can be used to predict the major product for which of the following reactions? A) 2-methylpentane + Br2(with light) B) 2-bromo-2-methylpentane + NaOCH2CH3 (in ethanol) C) 2-methyl-2-pentanol + PBr3 D) 2-methyl-2-pentanol + HCl Ans: B 35. The acid-catalyzed dehydration of the alcohol shown below gives a major product which results from a carbocation rearrangement. Identify this major product. A) A B) B Ans: A C) C D) D 36. Consider the following reaction. R = –CH3 or –C(CH3)3 Which statement(s) below is(are) correct? I. X is the major product based on Zaitsev's rule. II. The X:Y ratio is greater when R = –CH3 than when R = –C(CH3)3. III. The X:Y ratio is greater when R = –C(CH3)3 than when R = –CH3. A) I and II B) I and III C) only II D) only III Ans: A 37. How many different E2 products are expected in the reaction of 3-bromo-1,1dimethylcyclohexane with NaOCH2CH3? A) only 1 B) 2 C) 3 D) 4 Ans: B Page 9 Chem 341: Organic Chemistry, Prof. Jayaraman Sivaguru, Fall 2016. Chapter 7 Structure and Preparation of Alkenes - Elimination Reactions: Answers Prof. Jayaraman Sivaguru 38. Which one of the following compounds cannot undergo an E2 reaction? A) 1-bromo-2,2-dimethylbutane C) 1-bromo-3,3-dimethylbutane B) 1-bromo-2,3-dimethylbutane D) 2-bromo-2,3-dimethylbutane Ans: A 39. What is the major product of the reaction sequence shown below? A) 2-methyl-1-butene B) 2-methyl-2-butene Ans: B C) D) 3-methyl-1-butene 2-methylbutane 40. Which of the following compounds gives 4,4-dimethylcyclohexene as the exclusive E2 product? A) A B) B Ans: A C) C D) both A and B 41. How many stereoisomers are possible for the following diene? CH3CH=CHCH2CH2CH=CHCH2CH2CH3 A) only 1 B) two C) three D) four Ans: D Page 10 Chem 341: Organic Chemistry, Prof. Jayaraman Sivaguru, Fall 2016. Chapter 7 Structure and Preparation of Alkenes - Elimination Reactions: Answers Prof. Jayaraman Sivaguru 42. Based on Zaitsev's rule, which of the following is the major product of the reaction below? A) A B) B Ans: C C) C D) D 43. Which of the alkenes below has the Z-configuration? A) CH3 H3CO CH3 H3C B) OCH3 H3C C) OCH3 H N CH3 CH3 D) CH3 H3C H3C CH2CH3 A) A B) B Ans: B C) C D) D Cl CH3 OCH3 Page 11 Chem 341: Organic Chemistry, Prof. Jayaraman Sivaguru, Fall 2016. Chapter 7 Structure and Preparation of Alkenes - Elimination Reactions: Answers Prof. Jayaraman Sivaguru 44. Which alkene of formula C5H10 gives off the least heat (per mol) when burned? A) B) C) D) A) A B) B Ans: B C) C D) D 45. When a C=C is present in a molecule, what is the minimum number of atoms that must lie in a single plane? A) 2 B) 4 C) 6 D) 8 Ans: C 46. If you wanted to make compound III, starting with compound I or II, what would you do? OH ? I Br A) B) C) D) Ans: ? III II React I with H2SO4. React II with NaOEt. Either of the reactions in A or B above would work. Neither of the reactions in A or B above would work. B Page 12 Chem 341: Organic Chemistry, Prof. Jayaraman Sivaguru, Fall 2016. Chapter 7 Structure and Preparation of Alkenes - Elimination Reactions: Answers Prof. Jayaraman Sivaguru 47. Which compound would react slowest with KOtBu? Br Br D D A B Br D C A) A B) B Ans: A Br C) C D D D) D 48. Which reagent accomplishes the following? Cl OH ? A) HCl B) Cl2, light C) SOCl2 Ans: C D) NaCl 49. What would be the proper name of the molecule below? A) (E)-2-ethyl-2-butene B) (Z)-3-methyl-3-pentene Ans: C C) D) (E)-3-methyl-2-pentene (Z)-2-isohexene Page 13 Chem 341: Organic Chemistry, Prof. Jayaraman Sivaguru, Fall 2016. Chapter 7 Structure and Preparation of Alkenes - Elimination Reactions: Answers Prof. Jayaraman Sivaguru 50. Considering the SN1, SN2, E1, and E2 mechanisms, the energy diagram shown below corresponds to A) only the SN1 mechanism. B) only the SN2 mechanism. Ans: D C) D) both the SN1 and E1 mechanisms. both the SN2 and E2 mechanisms. 51. Which of the following bases works best to maximize the E2 product in the reaction shown below? A) KOCH2CH3 Ans: C B) NaOCH2CH3 C) NaOC(CH3)3 D) NaOH 52. In the solvolysis of t-butyl chloride, a minor product is 2-methylpropene, which results from the: A) B) C) D) Ans: E2 mechanism with OH¯ acting as the base. E2 mechanism with H2O acting as the base. E1 mechanism with OH¯ acting as the base. E1 mechanism with H2O acting as the base. D Page 14 Chem 341: Organic Chemistry, Prof. Jayaraman Sivaguru, Fall 2016. Chapter 7 Structure and Preparation of Alkenes - Elimination Reactions: Answers Prof. Jayaraman Sivaguru 53. Starting with 1-methylcyclohexene, which of the following reaction sequences is the best synthesis of the azide shown below? A) A B) B Ans: C C) C D) D 54. Consider the reaction of each of the following with 1-bromopentane. Which one would have the highest elimination/substitution ratio? A) NaOCH2CH3, ethanol, 55oC C) KOC(CH3)3, (CH3)3COH, 55oC B) NaSH, ethanol-water, 25oC D) KCN, DMSO, 40oC Ans: C 55. The major product expected from the reaction below would be CH3 Br NaCN ? CH3OH CH3 CH3 CN A A) A B) B Ans: C CH3 CH2 OCH3 C) C B D) D C D Page 15 Chem 341: Organic Chemistry, Prof. Jayaraman Sivaguru, Fall 2016.