Organic chemistry, 7e Brown Chapter 9

CHAPTER 9—NUCLEOPHILIC SUBSTITUTION AND BETA-ELIMINATION MULTIPLE CHOICE 1. Which of the following reactions corresponds to a substitution? a. propene ? 1,2-dibromopropane b. 1-iodopropane ? propene c. propene ? propane d. 1-iodopropane ? 1-bromopropane ANS: D 2. Which of the following reactions corresponds to a substitution? a. tert-butanol ? tert-butyl chloride b. tert-butanol ? 2-methylpropene c. 3,3-dimethyl-2-butanol ? 2,3-dimethyl-2-butene d. cyclohexene ? 1,2-dichlorocyclohexane ANS: A 3. Which of the following statements related to SN1 reactions is not true? a. The heterolysis of a bond between atoms which do not bear formal charges always produces a cation and an anion b. The charged carbon atom of a carbocation has a complete octet of valence shell electrons c. Carbocations are Lewis acids d. Nucleophiles seek centers of low electron density ANS: B 4. Which of the following statements related to SN1 reactions is not true? a. The SN1 reaction can be described as a heterolytic bond cleavage followed by nucleophilic attack b. Carbocations are electrophilic c. The charged carbon atom of a carbocation has an unfilled valence shell d. Nucleophiles are Lewis acids ANS: D 5. What is the equation for the rate of formation of tert-butyl alcohol from the reaction of tert-butyl bromide (t-BuBr) with water by an SN1 mechanism? a. Rate = k [t-BuBr] b. Rate = k [t-BuBr][H2O] c. Rate = k [H2O] d. Rate = k [t-BuBr]2 ANS: A 6. What is the equation for the rate of formation of 1-iodobutane from the reaction of 1-chlorobutane (BuCl) with NaI by an SN2 mechanism? a. Rate = k [BuCl] b. Rate = k [BuCl][NaI] c. Rate = k [NaI] d. Rate = k [BuCl]2 ANS: B 7. What is the equation for the rate of formation of 2-methoxypropane, (CH3CH(OCH3)CH3, from the reaction of 2-bromopropane (i-PrBr) with sodium methoxide (NaOCH3)? a. Rate = k [i-PrBr] b. Rate = k [i-PrBr]2 c. Rate = k [NaOCH3] d. Rate = k [i-PrBr][NaOCH3] ANS: D 8. What is the equation for the rate of formation of 2-methoxypropane, CH3CH(OCH3)CH3, from the reaction of 2-bromopropane (i-PrBr) with methanol? a. Rate = k [i-PrBr] b. Rate = k [i-PrBr]2 c. Rate = k [CH3OH] d. Rate = k [i-PrBr][CH3OH] ANS: A 9. The reaction of methyl iodide with sodium azide, NaN3, proceeds by an SN2 mechanism. What is the effect of doubling the concentration of NaN3 on the rate of the reaction? a. the rate remains the same b. the rate decreases by a factor of 2 c. the rate increases by a factor of 2 d. the rate increases by a factor of 4 ANS: C 10. The reaction of 1-bromopropane with sodium iodide gives 1-iodopropane. What is the effect of doubling the concentration of NaI on the rate of the reaction? a. the rate remains the same b. the rate decreases by a factor of 2 c. the rate increases by a factor of 2 d. the rate increases by a factor of 4 ANS: C 11. The reaction of tert-butyl bromide, (CH3)3CBr, with methanol in an inert solvent proceeds by an SN1 mechanism to give tert-butyl methyl ether, (CH3)3COCH3. What is the effect of doubling the concentration of methanol on the rate of the reaction? a. the rate remains the same b. the rate decreases by a factor of 2 c. the rate increases by a factor of 2 d. the rate increases by a factor of 4 ANS: A 12. The reaction of tert-butyl chloride, (CH3)3CCl, with water in an inert solvent gives tert-butyl alcohol, (CH3)3COH. What is the effect of doubling the concentration of water on the rate of the reaction? a. the rate remains the same b. the rate decreases by a factor of 2 c. the rate increases by a factor of 2 d. the rate increases by a factor of 4 ANS: A 13. Which of the following alkyl halides undergoes the fastest SN2 reaction with sodium azide, NaN3? a. 1-fluorohexane b. 1-chlorohexane c. 1-bromohexane d. 1-iodohexane ANS: D 14. Which of the following alkyl halides undergoes the fastest SN2 reaction with sodium cyanide, NaCN? a. methyl iodide b. ethyl iodide c. 2-iodopropane d. tert-butyl iodide ANS: A 15. Which of the following alkyl halides undergoes the fastest SN2 reaction with sodium methylthiolate, NaSMe? a. methyl iodide b. ethyl iodide c. 2-bromopropane d. tert-butyl chloride ANS: A 16. Which of the following alkyl halides undergoes the fastest solvolysis reaction with formic acid, HCOOH? a. tert-butyl fluoride b. tert-butyl chloride c. tert-butyl bromide d. tert-butyl iodide ANS: D 17. Which of the following alkyl halides undergoes the fastest solvolysis reaction with methanol, CH3OH? a. methyl chloride b. ethyl chloride c. 2-chloropropane d. tert-butyl chloride ANS: D 18. Which of the following alkyl halides undergoes the fastest solvolysis reaction with ethanol, CH3CH2OH? a. methyl fluoride b. ethyl bromide c. 2-chloropropane d. tert-butyl bromide ANS: D 19. Which of the following is best set of conditions for the preparation of tert-butanol? a. tert-butyl fluoride in water b. tert-butyl bromide in water c. tert-butyl fluoride and NaOH in DMSO d. tert-butyl bromide and NaOH in DMSO ANS: B 20. Which of the following is the best set of conditions for the preparation of tert-butyl methyl ether? a. tert-butyl fluoride and NaOCH3 in CH3OH b. methanol and sodium tert-butoxide in tert-butanol c. fluoromethane and sodium tert-butoxide in tert-butanol d. tert-butyl bromide and CH3OH ANS: D 21. What is the major product formed upon treatment of (R) 1-bromo-4-methylhexane with sodium cyanide? a. (R) 1-cyano-4-methylhexane b. (S) 1-cyano-4-methylhexane c. (R) 4-methyl-1-hexene d. (S) 4-methyl-1-hexene ANS: A 22. What is the major product formed upon treatment of (R) 2-bromohexane with sodium cyanide? a. (R) 2-cyanohexane b. (S) 2-cyanohexane c. 1-hexene d. 2-hexene ANS: B 23. What is the major organic product obtained from the following reaction? a. 1 b. 2 c. 3 d. 4 ANS: B 24. What is the major organic product obtained from the following reaction? a. 1 b. 2 c. 3 d. 4 ANS: A 25. What is the major organic product obtained from the following reaction? a. 1 b. 2 c. 3 d. 4 ANS: A 26. What is the major organic product obtained from the following reaction? a. 1 b. 2 c. 3 d. 4 ANS: B 27. What is the major organic product obtained from the following reaction? a. 1 b. 2 c. 3 d. 4 ANS: C 28. What is the major organic product(s) obtained from the following reaction? a. 1-hexyne b. 2-hexyne c. propene + propyne d. propane + propyne ANS: B 29. What is the major organic product(s) obtained from the following reaction? a. 3-methyl-1-pentyne b. 3-methyl-2-pentyne c. 1-propene + propyne d. 4-methyl-2-pentene ANS: C 30. What is(are) the major organic product(s) obtained from the following substitution reaction? a. only 1 b. only 2 c. only 3 d. a mixture of 1 and 2 ANS: A 31. What is(are) the major organic product(s) obtained from the following substitution reaction? a. only 1 b. only 2 c. only 3 d. a mixture of 1 and 2 ANS: D 32. What is(are) the major organic product(s) obtained from the following substitution reaction? a. only 1 b. only 2 c. only 1 and 2 d. 1, 2 and 3 ANS: D 33. What is(are) the major organic product(s) obtained from the following substitution reaction? a. only 1 b. only 2 c. only 1 and 2 d. 1, 2 and 3 ANS: D 34. In which of the following solvents would the reaction of 1-bromobutane with sodium azide, NaN3, proceed the fastest? a. acetic acid b. ethanol c. water d. acetonitrile ANS: D 35. Which of the following solvents is the best choice for the reaction of 1-chlorohexane with sodium bromide? a. dimethylsulfoxide b. water c. hexane d. toluene, PhCH3 ANS: A 36. Which of the following solvents is the best choice for the reaction of 1-chlorohexane with sodium bromide? a. water b. N,N-dimethylformamide c. hexane d. toluene, PhCH3 ANS: B 37. Which of the following anions is the most nucleophilic in polar protic solvents? a. F? b. Cl? c. Br? d. I? ANS: D 38. Which of the following anions is the most nucleophilic in polar aprotic solvents? a. F? b. Cl? c. Br? d. I? ANS: A 39. Which of the following compounds is the most nucleophilic in polar protic solvents? a. H2O b. NH3 c. H2S d. PH3 ANS: D 40. Which of the following is the most nucleophilic? a. sodium ethoxide b. acetic acid c. methanol d. water ANS: A 41. Which of the following anions is the best leaving group in an SN1 reaction? a. F? b. HO? c. NH2? d. Cl? ANS: D 42. Which of the following is the best leaving group in an SN2 reaction? a. F? b. H3C? c. CH3O2SO? d. HO? ANS: C 43. Which of the following statements is true regarding the reactivity of 1 and 2 with potassium tert-butoxide? a. 1 reacts faster than 2 b. 1 and 2 give different dehydrochlorinated products c. 2 reacts by elimination whereas 1 reacts by substitution d. 1 reacts by elimination whereas 2 reacts by substitution ANS: A 44. What is the major elimination product obtained from the following reaction? a. 1 b. 2 c. 3 d. 4 ANS: B 45. What is the major organic product obtained from the following reaction? a. 1 b. 2 c. 3 d. 4 ANS: A 46. Which of the following alkyl bromides reacts the slowest with NaSCH3 in DMF? a. 1 b. 2 c. 3 d. 4 ANS: A 47. Which of the following is most likely to undergo rearrangement during reaction with methanol? a. 1 b. 2 c. 3 d. 4 ANS: B 48. Which of the following compounds undergoes the most rapid hydrolysis reaction? a. 1 b. 2 c. 3 d. 4 ANS: B 49. Which of the following statements is not true regarding the SN2 reaction of (R)-2-bromobutane with sodium cyanide? a. the reaction proceeds with inversion of configuration b. the rate is proportional to the concentration of sodium cyanide c. the rate is proportional to the concentration of (R)-2-bromobutane d. the rate of the reaction is independent of the identity of the solvent ANS: D 50. Which of the following statements is true regarding the reaction of tert-butyl bromide with water? a. the rate is proportional to the concentration of tert-butyl bromide b. the rate is proportional to the concentration of water c. the rate is independent of the identity of the solvent d. the rate of the reaction is independent of the temperature ANS: A 51. Which of the following is not a characteristic of SN2 reactions? a. the electrophilic carbon undergoes inversion of stereochemistry b. the rate is proportional to the concentration of substrate c. the rate is proportional to the concentration of nucleophile d. the rate is independent of the solvent ANS: D 52. Which of the following is not a characteristic of SN1 reactions? a. the electrophilic carbon undergoes inversion of stereochemistry b. the rate is proportional to the concentration of substrate c. the reaction proceeds faster in a more polar solvent d. the rate is independent of the concentration of nucleophile ANS: A 53. What is the role of tetrabutylammonium chloride as a phase transfer catalyst in the reaction of 1-chlorooctane and sodium cyanide in a mixture of water and CH2Cl2? a. it transfers 1-chlorooctane into the aqueous phase b. it transfers cyanide anion into the organic phase c. it makes water and dichloromethane miscible d. it transfers the sodium cation into the organic phase ANS: B 54. Which of the following statements is not true regarding SN2 reactions? a. A carbocation intermediate is formed. b. The mechanism has only one step. c. Aprotic solvents are good choices for SN1 reactions. d. The stereochemical outcome is inversion at the carbon bearing the leaving group. ANS: A 55. Which of the following statements is not true regarding SN1 reactions? a. A carbocation intermediate is formed. b. The mechanism has only one step. c. Polar, protic solvents are good choices for SN1 reactions. d. The stereochemical outcome is racemization at the carbon bearing the leaving group. ANS: B 56. Which of the following energy diagrams represents the course of an exothermic SN1 reaction? a. 1 b. 2 c. 3 d. 4 ANS: A 57. Which of the following energy diagrams represents the course of an exothermic SN2 reaction? a. 1 b. 2 c. 3 d. 4 ANS: C 58. Which of the following energy diagrams represents the course of an exothermic E2 reaction? a. 1 b. 2 c. 3 d. 4 ANS: C 59. Which of the following energy diagrams represents the course of an exothermic E1 reaction? a. 1 b. 2 c. 3 d. 4 ANS: A 60. Which of the following represents the transition state of the rate-determining step in the SN1 reaction between tert-butyl chloride and water? a. 1 b. 2 c. 3 d. 4 ANS: B 61. Which of the following represents the transition state of the rate-determining step in the reaction between tert-butyl bromide and methanol? a. 1 b. 2 c. 3 d. 4 ANS: A 62. Which of the following represents the transition state of the reaction between methyl iodide and ammonia? a. 1 b. 2 c. 3 d. 4 ANS: C 63. Which of the following represents the transition state of the reaction between methyl bromide and sodium methylthiolate, NaSCH3? a. 1 b. 2 c. 3 d. 4 ANS: D 64. Which of the following represents the transition state of the rate-determining step in the reaction between 2-bromopropane and sodium methoxide leading to elimination? a. 1 b. 2 c. 3 d. 4 ANS: A 65. Which of the following represents the transition state of the rate-determining step in the reaction between 2-chloropropane and sodium amide leading to elimination? a. 1 b. 2 c. 3 d. 4 ANS: C 66. Which of the following represents the transition state of the rate-determining step in the reaction between tert-butyl bromide and methanol leading to elimination? a. 1 b. 2 c. 3 d. 4 ANS: B 67. Which of the following represents the transition state of the rate-determining step in the reaction between tert-butyl iodide and water leading to elimination? a. 1 b. 2 c. 3 d. 4 ANS: A 68. Which of the following sets consists of only polar aprotic solvents? a. water, hexane, methanol b. acetic acid, DMF, toluene c. DMSO, ethanol, acetonitrile d. DMF, acetonitrile, DMSO ANS: D 69. Which of the following sets consists of only polar protic solvents? a. water, DMF, DMSO b. acetic acid, methanol, water c. DMSO, ethanol, acetonitrile d. DMF, acetonitrile, DMSO ANS: B 70. Which of the following most favors elimination rather substitution in a reaction with 2-bromopropane? a. sodium methoxide b. sodium ethoxide c. sodium isoproxide d. sodium tert-butoxide ANS: D 71. Which of the following most favors elimination rather substitution in a reaction with sodium methoxide? a. bromomethane b. bromoethane c. 1-bromopropane d. 2-bromopropane ANS: D 72. What is the best choice of reagent to perform the following transformation? a. H2SO4 b. H2O c. NaOCH3 d. KOtBu ANS: D 73. What is the best choice of reagent to perform the following transformation? a. H2SO4 b. H2O c. NaOCH3 d. KOtBu ANS: A TRUE/FALSE 1. The following reaction would be classified as an elimination. ANS: F 2. HCl is the electrophile in the following reaction. ANS: T 3. In the following reaction the cyanide ion is both a nucleophile and a Lewis acid. ANS: F 4. The following energy diagram could represent an SN2 reaction. ANS: T 5. The rate law for the following reaction would be of the form Rate = k[A][B]. ANS: F 6. The first step in the mechanism for the following reaction would be the formation of a secondary carbocation. ANS: F 7. The following reaction would have a faster rate in a higher polarity solvent than one of low polarity. ANS: T 8. Consider the reaction below to answer the following question: The product of this reaction is ANS: T 9. Consider the reaction below to answer the following question: This reaction proceeds by an E1 mechanism. ANS: F COMPLETION Consider the pair of reactions below to answer the following question(s). a. or b. 1. Reaction ____ will be faster. ANS: b 2. These reactions are classified as ________________reactions. ANS: substitution 3. The mechanism for these reactions is _______. ANS: SN2 Sn2 SN2 Sn2 4. In the reactions a and b if concentration of OH– and SH–, respectively, were doubled, the rate of the reactions would ___________. ANS: double increase by a factor of two Consider the pair of reactions below to answer the following question(s). a. or b. 5. The solvent in these reactions would be classified as ______ ________. ANS: polar aprotic aprotic polar 6. The nucleophile is these reactions is________. ANS: Iodide iodide ion I– 7. Reaction ____ is faster. ANS: b Consider the reaction below to answer the following question(s). 8. Compound B by is formed by an _____ mechanism. ANS: SN1 Sn1 SN1 Sn1 9. Compound C is formed by an _____ mechanism. ANS: E1 For each substrate below, choose which reaction type is favored. Place the letter of the reaction type in the blank to the left of the substrate. a. SN1 b. SN2 c. E1 d. E2 10. ______ ANS: b 11. _____ ANS: d Classify each of the following species as a. an electrophile. b. a nucleophile. c. either an electrophile or a nucleophile. Place the letter of the choice in the blank to the left of the formula. 12. ________ ANS: c 13. ________ ANS: a 14. ________ ANS: b PROBLEM 1. Draw all of the chloroalkanes that undergo base-promoted dehydrochlorination to form the following alkene? ANS: 2. Draw all of the chloroalkanes that undergo base-promoted dehydrochlorination to form the following alkene? ANS: 3. Draw all of the chloroalkanes that undergo base-promoted dehydrochlorination to form the following alkene? ANS: 4. Draw all of the chloroalkanes that undergo base-promoted dehydrochlorination to form the following alkene? ANS: 5. What is the major organic product obtained from the following reaction? ANS: 6. What is the major organic product obtained from the following reaction? ANS: 7. What is the major organic product obtained from the following reaction? ANS: 8. What is the major organic product obtained from the following reaction? ANS: 9. What is the major organic product obtained from the following reaction? ANS: 10. What is the major organic product obtained from the following reaction? ANS: ANS 11. What is the major organic product obtained from the following reaction? ANS: 12. What is the major organic product obtained from the following reaction? ANS: 13. What is the major organic product obtained from the following reaction? ANS: 14. What is the major organic product obtained from the following reaction? ANS: 15. Provide a neatly drawn mechanism for the following reaction, including curved arrows to show the movement of pairs of electrons and the structure of reactive intermediates. ANS: The reaction proceeds in three steps: 1. Dissociation by cleavage of the carbon-chlorine bond to afford a tertiary carbocation 2. Nucleophilic addition of water to the carbocation 3. Deprotonation of oxygen 16. Provide a neatly drawn mechanism for the following reaction, including curved arrows to show the movement of pairs of electrons and the structure of reactive intermediates. ANS: The reaction proceeds in a single step: Concerted nucleophilic attack on the electrophilic carbon atom with departure of bromide anion as the leaving group.