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UTA / Chemistry / CHEM 2321 / which alkene would react with cold dilute alkaline permanganate soluti

which alkene would react with cold dilute alkaline permanganate soluti

which alkene would react with cold dilute alkaline permanganate soluti

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School: University of Texas at Arlington
Department: Chemistry
Course: Organic Chemistry I
Professor: Junha jeon
Term: Fall 2016
Tags: Alkenes, Elimination, addition, and reactions
Cost: 50
Name: CHEM2321 Midterm 3 Studyguide
Description: Chapter 8- Alkenes: Structure and Preparation via Elimination Reactions Chapter 9- Addition Reactions of Alkenes
Uploaded: 11/27/2016
190 Pages 1058 Views 0 Unlocks
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Chapter 8 MULTIPLE CHOICE QUESTIONS  Topic: Structure Elucidation  1. An alkene adds hydrogen in the presence of a catalyst to give 3,4-dimethylhexane.  Ozonolysis of the alkene followed by treatment with zinc and acetic acid gives a single  organic product. The structure of the alkene is:  A)  B)  CH3 CH3CH=C-CHCH2CH3 CH3 CH3 CH3CH2C=CCH3 (cis or trans) (cis or trans) C)  CH3 CH2CH3 D)  E)  CH2=CCH2CHCH2CH3 CH3 CH2 CH3CH2CCHCH2CH3 CH3 CH3 CH3CH2CHCHCH=CH2 CH3 Ans: B 241 Chapter 8 Topic: Structure Elucidation  2. Ozonolysis of compound Z yields the products shown below. What is the structure of Z? O OO Z 2HCH + CH3CCH2CH 1) O3 2) Zn, HOAc O I II III O H


What is the structure of Z?



      A) I  B) II  C) III  D) IV  E) V  Ans: B IV V 242 Chapter 8 Topic: Structure Elucidation  3. Compound C has the molecular formula C7H12. On catalytic hydrogenation, 1 mol of C absorbs 1 mol of hydrogen and yields a compound with the molecular formula C7H14.  On ozonolysis and subsequent treatment with zinc and acetic acid, C yields only:  O O    The structure of C is:  I II III IV V A) I  B) II  C) III  D) IV  E) V  Ans: E  Topic: Structure Elucidation  4. Compound X has the molecular formula C6H10. X decolorizes bromine in carbon  tetrachloride. X also shows IR absorption at about 3300 cm-1. When treated with  excess hydrogen and a nickel catalyst, X yields 2-methylpentane. The most likely  structure for X is:  A)  B)  C)  D)  E)  Ans: D 243 Chapter 8 Topic: Structure Elucidation  5. An unknown compound, A, has the molecular formula C7H12. On oxidation with hot  aqueous potassium permanganate, A yields CH3CH2COOH and (CH3)2CHCOOH.  Which of the following structures best represents A?  A)  B)  C)  D)  E)  Ans: C 244 Chapter 8 Topic: Structure Elucidation  6. Determine a possible structure for an alkene, X, formula C9H14, on the basis of the  following information: X adds one mole of hydrogen on catalytic hydrogenation. On  treatment with hot basic KMnO4 followed by acidification, X yields the following  dicarboxylic acid.  HO O  OH O A possible structure for X might be:  I II III IV V   A) I  B) II  C) III  D) IV  E) V  Ans: C  Topic: Structure Elucidation  7. An optically active compound, Y, with the molecular formula C7H12 gives a positive test  with cold dilute KMnO4 and shows IR absorption at about 3300 cm-1. On catalytic  hydrogenation, Y yields Z(C7H16) and Z is also optically active. Which is a possible  structure for Y?  A) CH3CH2CH2CH2CH2C≡CH  B) (CH3)2CHCH2CH2C≡CH  C) CH3CH2CH(CH3)CH2C≡CH  D) CH3CH2CH(CH3)C≡CCH3 E) CH2=CHCH(CH3)CH2CH=CH2 Ans: C 245 Chapter 8 Topic: Structure Elucidation  8. One mole of an optically active compound, X, with the molecular formula C6H8 reacts  with three moles of hydrogen in the presence of a catalyst to yield an optically inactive  product that cannot be resolved. X also exhibits IR absorption at approximately 3300  cm-1. Which is a possible structure for X?  A) (E)-4-hexen-1-yne  B) (Z)-4-hexen-1-yne  C) (E)-2-hexen-4-yne  D) 2-methyl-1-penten-3-yne  E) 3-methyl-1-penten-4-yne  Ans: E  Topic: Structure Elucidation  9. An alkene with the molecular formula C10H18 is treated with ozone and then with zinc  and acetic acid. The product isolated from these reactions is:  OO  What is the structure of the alkene?  I   A) I  B) II  C) III  D) IV  E) V  Ans: C II III IV V 246 Chapter 8 Topic: Structure Elucidation  10. An optically active compound, A, with the molecular formula C7H12 reacts with cold  dilute KMnO4 and gives IR absorption at about 3300 cm-1. On catalytic hydrogenation,  A is converted to B (C7H16) and B is also optically active. Which is a possible structure  for A?  I   A) I  B) II  C) III  D) IV  E) V  Ans: E  II III IV V Topic: Structure Elucidation  11. Which substance would undergo the following reaction?  i. O3 H ii. Zn, HOAc ?O+ H O A) 4-Hexen-1-yne r B) 3-methyl-1-hexene  C) (E)-2-hexene  D) (Z)-2-hexene  E) 4-methyl-1-hexene  Ans: E 247 Chapter 8 Topic: Structure Elucidation  12. Which alkene would yield only CH3CH2COOH on oxidation with hot alkaline  potassium permanganate (followed by acid work-up)?  A) (E)-2-hexene  B) (Z)-2-hexene  C) 2-methyl-2-pentene  D) (E)-3-hexene  E) (E)-4-methyl-2-pentene  Ans: D  Topic: Structure Elucidation  13. An unknown compound, B, has the molecular formula C7H12. On catalytic  hydrogenation 1 mol of B absorbs 2 mol of hydrogen and yields 2-methylhexane. B has  significant IR absorption band at about 3300 and 2200 cm-1. Which compound best  represents B?  A) 3-methyl-1-hexyne  B) 5-methyl-2-hexyne  C) 5-methyl-1,3-hexadiene  D) 5-methyl-1-hexyne  E) 2-methyl-1,5-hexadiene  Ans: D  Topic: Structure Elucidation  14. What compound would yield an equimolar mixture of CH3CH2CH2CHO and CH3CHO  upon treatment with O3, followed by Zn/HOAc?  A) 1-Hexene  B) cis-2-Hexene  C) trans-2-Hexene  D) More than one of these  E) None of these  Ans: D  Topic: Structure Elucidation  15. An alkene with the molecular formula C8H16 undergoes ozonolysis to yield a mixture of  (CH3)2C=O and (CH3)3CCHO. The alkene is:  A) 2,2-Dimethyl-2-hexene  B) 2,3-Dimethyl-2-hexene  C) 2,4-Dimethyl-2-hexene  D) 2,4,4-Trimethyl-2-pentene  E) More than one of the above is a possible answer.  Ans: D 248 Chapter 8 Topic: Structure Elucidation  16. Which of the following would decolorize bromine in carbon tetrachloride and yield a  ketone upon reaction with sulfuric acid in the presence of catalytic amounts of HgSO4?  A) CH3CH=CHCH3 B) CH3CH=CH2 C) CH3CH2C≡CH  D) CH3CH2CH2CH3 E) All of these would give positive results in each test.  Ans: C  Topic: Structure Elucidation  17. Which of these compounds will react with cold concd. H2SO4, as well as Br2 in CCl4 ?  A) CH3CH2CH=CHCH3 B) CH3CH2CH2CH=CH2 C) CH3CH2C≡CCH3 D) (CH3)2CHC≡CH  E) All of these  Ans: E  Topic: Structure Elucidation  18. Which of the following reagents might serve as the basis for a simple chemical test that  would distinguish between pure 1-pentene and pure pentane?  A) Bromine in carbon tetrachloride  B) Dilute aqueous potassium permanganate  C) Concentrated sulfuric acid  D) All of the above  E) Answers A) and B) only  Ans: D  Topic: Structure Elucidation  19. Which reagent or test could be used to distinguish between 3-pentyne and 1-pentyne?  A) Br2/CCl4 B) IR examination  C) Concd. H2SO4 D) KMnO4,OH E) None of these  Ans: B 249 Chapter 8 Topic: Structure Elucidation  20. Which reagent or test could be used to distinguish between 2-methyl-2-pentene and 2- methylpentane?  A) Br2/CCl4 B) KMnO4, OH− C) Concd. H2SO4 D) Two of the above  E) All of the above  Ans: E  Topic: Structure Elucidation  21. Which of the following could be used to distinguish between 1-octyne and 3-octyne?  A) Treatment with 2 mol of HX  B) Addition of water  C) Reaction with KMnO4 D) Decolorization of bromine in CCl4 E) IR examination  Ans: E  Topic: Structure Elucidation  22. A reagent or test that could be used to distinguish between 1-pentene and 1-pentyne  would be:  A) Bromine in carbon tetrachloride  B) Dilute aqueous potassium permanganate  C) CrO3 in H2SO4 D) H2SO4 E) IR examination  Ans: E  Topic: Structure Elucidation  23. Which of the following could be used as the basis for a simple test that would  distinguish between 1-pentyne and pentane?  A) IR examination  B) Br2/CCl4 C) KMnO4/H2O  D) Two of these  E) All of these  Ans: E 250 Chapter 8 Topic: Reaction Products  24. Treating 1-methylcyclohexene with H3O+ would yield primarily which of these?  HO HO HO I A) I and V  B) II  C) III and V  D) IV  E) I, III and V  Ans: D  HO II III OH IV V Topic: Reaction Products  25. What would be the major product of the following reaction?  HCl Cl Cl I A) I  B) II  Cl Cl IV II Cl V III Cl C) III  D) IV  E) V  Ans: B 251 Chapter 8 Topic: Reaction Products  26. Treating 1-methylcyclohexene with HCl would yield primarily which of these?  H3C Cl A) I  B) II  C) III  D) IV  E) V  H3C Cl I H3C Cl IV II V H3C Cl III Cl Ans: C  Topic: Reaction Products  27. Which product would you expect from the following reaction?  H3O+ H2O OH OH I A) I  B) II  OH IV II V OH III C) III  D) IV  E) V  Ans: D 252 Chapter 8 Topic: Reaction Products  28. The reaction of Br2/CCl4 to cyclohexene would produce the compound(s) represented  by structure(s):  H Br H Br Br Br H H Br Br H H I II III A) I alone  B) II alone  C) II and III  D) III alone  E) I , II and II  Ans: C  Topic: Reaction Products  29. What product would you expect from addition of deuterium chloride to 2-cyclohexyl-4- methyl-2-pentene?  D Cl I II Cl D IV A) I  B) II  C) III  D) IV  E) V  Ans: B Cl D H 253 D Cl III D Cl V Chapter 8 Topic: Reaction Products  30. What is the chief product of the reaction of IBr with 2-methyl-2-pentene?  A) 2-bromo-3-iodo-2-methylpentane  B) 3-bromo-2-iodo-2-methylpentane  C) 1-bromo-2-iodo-2-methylpentane  D) 2-bromo-1-iodo-2-methylpentane  E) All of the above  Ans: A  Topic: Reaction Products  31. What is the chief product of the acid-catalyzed hydration of 2,5-dimethyl-2-hexene?  A) 2,5-dimethyl-1-hexanol  B) 2,5-dimethyl-2-hexanol  C) 2,5-dimethyl-3-hexanol  D) 2,5-dimethyl-2,3-hexanediol  E) 2,5-dimethyl-3,4-hexanediol  Ans: B  Topic: Reaction Products  32. What product would result from the following reaction?  KMnO4, H2O cold, dilute ? CO2H O K MnO4 OH OH I II OH OH IV A) I  B) II  C) III  D) IV  E) V  III OH OH V Ans: C 254 Chapter 8 Topic: Reaction Products  33. Acid-catalyzed hydration of 2-methyl-1-butene would yield which of the following?  A) (CH3)2C(OH)CH2CH3 B) CH2OHCH(CH3)CH2CH3 C) (CH3)2CHCHOHCH3 D) (CH3)2CHCH2CH2OH  E) CH3CH2CH(CH3)CH2OH  Ans: A  Topic: Reaction Products  34. Which of these is not formed when cyclopentene reacts with an aqueous solution of  bromine?  OH Br OH Br Br Br Br Br OH OH I II III IV V A) I  B) II  C) III  D) IV  E) V  Ans: E  Topic: Reaction Products  35. What would be the major product of the following reaction?  Br2, H2O? Br Br OH Br OH OH Br Br Br OH I II III IV V A) I  B) II  C) III  D) IV  E) V  Ans: A 255 Chapter 8 Topic: Reaction Products  36. Addition of hydrogen chloride to the following molecule would produce:  Cl Cl Cl Cl Cl Cl HCl Cl Cl ? Cl Cl Cl I II III A) I and II  B) II and III  C) I and IV  D) V  E) All of the above are equally likely to be formed  Ans: A 256 IV V Chapter 8 Topic: Reaction Products  37. In addition to the expected major product, which compound may be reasonably  anticipated as a by-product in the hydroxylation of R-2-methylcyclohexene with cold  alkaline permanganate?  H3C H i. KMnO4, H2O  cold, dilute ii. H3O+ ? H3C H OH OH H3C H OH H H3C H OO I II H CH3 OO III H CH3 OH O O A) I  B) II  C) III  D) IV  E) V  Ans: E IV OH 257 V Chapter 8 Topic: Reaction Products  38. Select the structure of the major product formed in the following reaction.  2 HCl Cl ? Cl Cl Cl I II Cl Cl IV A) I  B) II  C) III  D) IV  E) V  Cl V III Cl Ans: D  Topic: Reaction Products  39. Which of these compounds is not formed when gaseous ethene is bubbled into an  aqueous solution of bromine, sodium chloride and sodium nitrate?  A) BrCH2CH2Br  B) BrCH2CH2Cl  C) BrCH2CH2OH  D) ClCH2CH2OH  E) BrCH2CH2ONO2 Ans: D 258 Chapter 8 Topic: Reaction Products  40. Select the structure of the major product formed in the following reaction.  2 Cl2 Cl ? Cl Cl Cl Cl Cl Cl I II Cl Cl IV A) I  B) II  C) III  D) IV  E) V  Cl V III Cl Ans: C 259 Chapter 8 Topic: Reaction Products  41. Addition of excess HBr to 2-methyl-3-heptyne would produce:  2-methyl-3,3-dichloroheptane 2-methyl-2,3-dichloroheptane   I II  2-methyl-4,4-dichloroheptane 2-methyl-3,4-dichloroheptane   III IV  2-methyl-3-chloroheptene   V  A) I and II  B) I and III  C) II and IV  D) V  E) All of the above  Ans: B  Topic: Reaction Products  42. What would be the major product of the following reaction?  CH3 CH3 Br2, CCl4 CH3 ? CH3 H H   Br Br C3H7 I Br Br H H C3H7 II H Br Br H C3H7 III Br H H Br C3H7 IV A) Equal amounts of I and II  B) Equal amounts of II and III  C) Equal amounts of III and IV  D) I and II as major products, III and IV as minor products  E) All of the above in equal amounts  Ans: A 260 Chapter 8 Topic: Reaction Products  43. What would be the major product of the following reaction?  C2H5 C2H5 Br2, CCl4 C2H5 ? C2H5 H3C H Br Br C3H7 Br Br CH3 H C3H7 H3C Br Br H C3H7 Br H CH3 Br C3H7 I II III A) Equal amounts of I and II  B) Equal amounts of II and III  C) Equal amounts of III and IV  IV D) I and II as major products, III and IV as minor products  E) All of the above in equal amounts  Ans: A  Topic: Reaction Products  44. Hydroxylation of cis-2-pentene with cold alkaline KMnO4 yields  H H CH3 OH OH C2H5 HO HO CH3 H H C2H5 H HO CH3 OH H C2H5 HO H CH3 H OH C2H5 I II III A) Equal amounts of I and II  B) Equal amounts of II and III  C) Equal amounts of III and IV  IV D) I and II as major products, III and IV as minor products  E) All of the above in equal amounts  Ans: B 261 Chapter 8 Topic: Reaction Products  45. The reaction of BrCl (bromine monochloride) with 1-methylcyclopentene will produce  as the predominant product:  CH3 CH3 CH3 CH3 CH2Cl Br Br Cl  + Cl Br  + Br Cl  + Cl Br  +  + enantiomer enantiomer enantiomer enantiomer enantiomer A) I  B) II  C) III  D) IV  E) V  I II III IV V Ans: D  Topic: Reaction Products  46. Reaction of trans-2-hexene with a solution of Br2 in CCl4 produces:  Br H Br H H Br H Br Br H H Br I II III Br H H H Br Br V A) I and II  B) II and V  C) III and IV  D) IV and V  E) V  Ans: C 262 Br H IV Chapter 8 Topic: Reaction Products  47. When either cis- or trans-2-butene is treated with hydrogen chloride in ethanol, the  product mixture that results includes:  A) CH3CH2CH2CH2Cl  B) CH3CH2CH2CH2OCH2CH3 C) CH3CH2CH(CH3)OCH2CH3 D) (CH3)3CCl  E) (CH3)2CHCH2OCH2CH3 Ans: C  Topic: Reaction Products  48. What is the major product of the following reaction?  ? OH H2SO4, H2O  HgSO4 OH OH I II O IV A) I  B) II  C) III  D) IV  E) V  OH V III O Ans: D  Topic: Reaction Products  49. Addition of 2 mol of HCl to 1-butyne would yield:  A) CH3CH2CH2CHCl2 B) CH3CH2CCl2CH3 C) CH3CH2CHClCH2Cl  D) CH3CH2CH=CHCl  E) CH3CHClCHClCH3 Ans: B 263 Chapter 8 Topic: Reaction Products  50. Consider the addition of HCl to 3-methyl-1-butene. The major product of the reaction  would be:  A) 1-Chloro-2-methylbutane  B) 1-Chloro-3-methylbutane  C) 2-Chloro-2-methylbutane  D) 2-Chloro-3-methylbutane  E) 1-Chloropentane  Ans: C  Topic: Reaction Products  51. What is the final product of the following synthesis?  C4H8 HO 2-Butyne CH3 H2 Ni2B (P-2) CH3 i. OsO4 ii. NaHSO4 CH3 Final Product CH3 OH HO H HO H H OH H H CH3 HO H CH3 H OH CH3 HO H CH3 I II III IV A) I  B) II  C) III  D) IV  E) An equimolar mixture of III and IV  Ans: B  Topic: Synthetic Strategy  52. A synthetic strategy for converting trans-2-butene into pure cis-2-butene would consist  of which of the following?  A) Reaction with H2, Ni2B (P-2)  B) Reaction with i) Br2, CCl4; ii) 2 NaNH2, NH3(l); iii) Na, NH3 (l)  C) Reaction with H3O+, heat  D) Reaction with i) Br2, CCl4; ii) 2 NaNH2, NH3(l); iii) H2, Ni2B (P-2)  E) None of these will successfully effect the desired transformation  Ans: D 264 Chapter 8 Topic: Synthetic Strategy  53. Which reagent(s) given below could be used to synthesize cis-1,2-cycloheptanediol  from cycloheptene?  A) KMnO4, OH−, 5oC  B) KMnO4, H3O+, 75oC  C) H2SO4, heat  D) All of these  E) None of these  Ans: A  Topic: Synthetic Strategy  54. Which reaction sequence would convert cis-2-butene to trans-2-butene?  A) Br2/CCl4; then 2 NaNH2; then H2/Ni2B(P-2)  B) Br2/CCl4; then 2 NaNH2; then Li/liq. NH3 C) H3O+, heat; then cold dilute KMnO4 D) HBr; then NaNH2; then H2, Pt  E) None of these  Ans: B  Topic: Synthetic Strategy  55. The conversion of ethylene to vinyl bromide can be accomplished by use of these  reagents in the order indicated.  A) (1) HBr; (2) NaOC2H5 B) (1) Br2; (2) NaOC2H5 C) (1) Br2; (2) H2O  D) (1) NaNH2; (2) HBr  E) (1) HBr; (2) H2SO4 Ans: B  Topic: Synthetic Strategy  56. Cyclohexene is treated with cold dilute alkaline KMnO4. Assuming syn addition, the  spatial arrangement of the two hydroxyl groups in the product would be:  A) equatorial-axial  B) axial-axial  C) equatorial-equatorial  D) coplanar  E) trans  Ans: A 265 Chapter 8 Topic: Synthetic Strategy  57. Which of the following reactions of cyclobutene would yield a meso product?  A) Reaction with H3O+, H2O  B) Reaction with Br2, CCl4 C) Reaction with Cl2, CCl4 D) Reaction with D2, Pt  E) Reaction with hot, alkaline KMnO4, followed by acid workup  Ans: E  Topic: Reaction Products  58. How many compounds are possible from the addition of bromine to CH2=CHCH2CH3 (counting stereoisomers separately)?  A) One  B) Two  C) Three  D) Four  E) Five  Ans: B  Topic: Reaction Products  59. Which alkene would react with cold dilute alkaline permanganate solution to form an  optically inactive and irresolvable product?  A)  B)  C)  D)  E)  Ans: C 266 Chapter 8 Topic: Reaction Products  60. Which reaction of an alkene proceeds with anti addition?  A) Hydroboration/oxidation  B) Bromination  C) Oxidation with cold KMnO4 D) Hydrogenation  E) Oxymercuration-demercuration  Ans: B  Topic: Reaction Products  61. A pair of enantiomers results from which of these reactions?  A) cyclopentene + cold, dil. KMnO4 ••••ο B) trans-2-butene + Br2 ••••ο C) 1-pentene + HCl ••••ο D) cis-2-butene + D2/Pt ••••ο E) cyclobutene + OsO4, then Na2SO3 ••••ο  Ans: C  Topic: Reaction Products  62. Which reaction would yield a racemic product?  A) cyclopentene + D2/Pt ••••ο B) Cyclopentene + OsO4, then Na2SO3 ••••ο C) cyclopentene + Br2/H2O ••••ο D) Cyclopentene + cold, dilute KMnO4 ••••ο E) Cyclopentene + dilute H2SO4 ••••ο Ans: C  Topic: Reaction Products  63. 3,3-dimethylcyclohexene is subjected to reaction with cold, dilute KMnO4, to give 3,3- dimethyl-1,2-cyclohexanediol. In the most stable conformation of the product, the  hydroxyl groups would be:  A) both axial  B) both equatorial  C) axial-equatorial  D) coplanar  E) None of these  Ans: B 267 Chapter 8 Topic: Reaction Products  64. Cyclohexene reacts with bromine to yield 1,2-dibromocyclohexane. Molecules of the  product would:  A) be a racemic form and, in their most stable conformation, they would have both bromine  atoms equatorial.  B) be a racemic form and, in their most stable conformation, they would have one bromine  atom equatorial and one axial.  C) be a meso compound and, in its most stable conformation, it would have both bromine  atoms equatorial.  D) be a meso compound and, in its most stable conformation, it would have one bromine  atom equatorial and one axial.  E) be a pair of diastereomers and, in their most stable conformation, one would have the  bromines equatorial and axial, and the other would have the bromines equatorial and  equatorial.  Ans: A  Topic: Reaction Products  65. Which reaction would yield a meso compound?  A) Br2/CCl4 cis-2-Butene B) cis-2-ButeneH2/Pd C) cis-2-Butene i) OsO4 ii) NaHSO3 D) dil KMnO4 trans-2-Butene E) None of these  Ans: C  Topic: Reaction Products   5oC 66. Which reaction would give a meso compound as the product?  A) Cyclopentene + Br2/CCl4 B) Cyclopentene + OsO4, then NaHSO3 C) Cyclopentene + RCO3H, then H3O+ D) Cyclopentene + Cl2, H2O  E) More than one of these  Ans: B 268 Chapter 8 Topic: Reaction Products  67. Which of the following reactions would yield the final product as a racemic form?  A) Cyclohexene + a peroxy acid, then H3O+ B) Cyclohexene + cold, dilute KMnO4 and OH C) Cyclohexene + HCl  D) Cyclohexene + OsO4, then NaHSO3 E) Cyclohexene + D2/Pt  Ans: A  Topic: Reaction Products  68. (R)-3-Chloro-1-butene reacts with HCl by Markovnikov addition, and the products are  separated by gas chromatography. How many total fractions would be obtained and  how many would be optically active?  A) One optically active fraction only  B) One optically active fraction and one optically inactive  C) Two optically active fractions  D) One optically active fraction and two optically inactive  E) Two optically active fractions and one optically inactive  Ans: B  Topic: Reaction Products  69. The interaction of the π bond of an alkene with an electrophile can initially result in the  formation of a species termed a π complex. Which of these cannot combine with an  alkene to form a π complex?  A) H+ B) NH3 C) Ag+ D) Hg2+ E) BF3 Ans: B  Topic: Reaction Products  70. Markovnikov addition of HI to 2-methyl-2-butene involves:  A) initial attack by an iodide ion.  B) initial attack by an iodine atom.  C) isomerization of 2-iodo-2-methylbutene.  D) formation of a carbocation at C-2.  E) formation of carbocation at C-3.  Ans: D 269 Chapter 8 Topic: Reaction Products  71. Which reaction is NOT stereospecific?  Br2/CCl4 trans-2-Butene cis-2-Pentene I II 1-MethylcyclohexeneH2/Pd III Br2/H2O 2-Methyl-2-heptene trans-2-Hexene dil KMnO4  5oC HBr IV V A) I  B) II  C) III  D) IV  E) V  Ans: E 270 Chapter 8 Topic: Reaction Products  72. Which reaction is regioselective?  Cl I II III IV   A) I  B) II  C) III  D) IV  E) None of these  Ans: A  ICl Br2 KMnO4 D2/Ni I Br Br OH OH H DD H Topic: General Information  73. The thermodynamic parameters at 298 K for the following reaction are given below.  CH2=CH2 + HCl gas phase CH3CH2Cl ∍Hº = -64.9 kJ mol-1   ∍Sº = -131 J K-1 mol-1   ∍Gº = -25.8 kJ mol-1  Which of the following statements is true of the reaction?  A) Both ∍Hº and ∍Sº favor product formation.  B) Neither ∍Hº nor ∍Sº favors product formation.  C) The entropy term is unfavorable but the formation of ethyl chloride is favored.  D) The entropy term is favorable but the formation of ethyl chloride is not favored.  E) The sign of ∍Gº indicates that the reaction cannot occur as written.  Ans: C 271 Chapter 8 Topic: Reaction Products  74. In general, when the addition of an unsymmetrical electrophilic reagent to an  unsymmetrical alkene forms the product predicted by Markovnikov's rule, that occurs  because:  A) the product is statistically favored.  B) steric hindrance favors its formation.  C) it is formed via the more/most stable carbocation.  D) it is the more/most stable product.  E) All of the above are reasons.  Ans: C  Topic: General Information  75. Which of these compounds belongs to the class of substances commonly known as  "halohydrins"?  A) BrCH2CH2Cl  B) ClCH2CO2H C) ICH2CH2OH  D) FCH2CH2NH2 E) HOCH2COCl  Ans: C  Topic: General Information  76. Which alkene would you expect to be most reactive toward acid-catalyzed hydration?  A) 1 pentene  B) trans-2-pentene  C) cis-2-pentene  D) 2-methyl-1butene  E) All of these would be equally reactive.  Ans: D  Topic: General Information  77. The most resistant compound to the action of hot alkaline KMnO4 is:  A) Pentane  B) 1-Pentene  C) 2-Pentene  D) 2-Pentyne  E) Cyclopentene  Ans: A 272 Chapter 8 Topic: General Information  78. 2-Pentyne will not react with:  A) H2, Pt  B) Br2 C) NH3 D) H2SO4 E) KMnO4/H2O  Ans: C  Topic: General Information  79. Consider the ozonolysis products obtained from all the unbranched and unsymmetrical isomers of heptene. The reaction product in each case would consist of:  A) a single aldehyde.  B) an aldehyde and a ketone.  C) two different ketones.  D) two different aldehydes.  E) a single ketone.  Ans: D  SHORT ANSWER QUESTIONS  Topic: General Information  80. The rule that correctly predicts the regiochemistry of most ionic additions to alkenes is  called ____________________.  Ans: Markovnikov's Rule  Topic: General Information  81. When a reaction that could potentially yield two or more constitutional isomers instead  produces only one as the major product, the reaction is said to be  _____________________.  Ans: regioselective  Topic: General Information  82. When a particular stereoisomer reacts in such a way that it gives a particular  stereoisomer as a product, even if more than one stereoisomer is theoretically possible,  the reaction is said to be _____________.  Ans: stereospecific 273 Chapter 8 Topic: General Information  83. A reaction in which the reactant is not necessarily chiral but still produces primarily one  stereoisomeric form of the product (or a specific subset of the possible stereoisomers) is  referred to as a _________________ reaction.  Ans: stereoselective  Topic: General Information  84. Hydroboration-oxidation is a reaction with _________ stereochemistry and  ________________ regiochemistry.  Ans: syn, anti-Markovnikov  Topic: General Information  85. Even when one or more stereogenic centers are produced as the result of an addition  reaction to an alkene, the product is always formed as a racemic mixture. Why is that?  Ans: Because alkenes are planar, and the reagent can add from either face.  Topic: General Information  86. The “decolorization” of molecular bromine is often used as a functional group test to  detect the presence of ________________.  Ans: carbon-carbon multiple bonds; or, alkenes and alkynes  Topic: General Information  87. Neutral divalent carbon compounds are called ___________.  Ans: carbenes  Topic: General Information  88. Carbenes are frequently produced by Δ-elimination reactions. These are reactions in  which the proton being lost and the leaving group are ___________.  Ans: both attached to the same carbon  Topic: General Information  89. π bonds are quite susceptible to reaction with electron-seeking reagents, also referred to as  ____________________.  Ans: electrophiles 274 Chapter 8 Topic: Reaction Sequence  90. Predict the final product(s) obtained when (2R,3R)-2-bromo-3-methylpentane is subjected to  the following sequence of reactions, briefly explaining your rationale. Provide regiochemical  and stereochemical details as relevant.  i) NaOC2H5/C2H5OH, heat  ii) BH3, THF  iii) H2O2, OH− Ans: Br H H3C H NaOC2H5 C2H5OH  (E2: anti H CH3 E-3-methyl-2-hexene Hydroboration/oxidation:  overall  elimination) (2R,3R) Anti-Markovnikov,  syn addition of H2O H OH + HO H H3C H H CH3 (2S,3R) (2R,3S) 3-methyl-2-pentanol Heating with sodium ethoxide results in E2 elimination; the anti- elimination leads to  the formation of E-3-methyl-2-hexene as the major product. Subsequent hydroboration  oxidation is regioselective (anti-Markovnikov) and stereospecific (syn), resulting in the  formation of racemic (2S,3R & 2R,3S) 3-methyl-2-pentanol. The other diastereomer  pair (2S,3S & 2R,3R) is not expected to be obtained.  Topic: Reaction Products  91. Provide a mechanistic explanation for the following observation: The same major product is  obtained when 2-ethyl-1-hexene and 3-methyl-2-heptene are allowed to react with HCl.  Ans: HCl HCl most stable  carbocation Cl Both alkenes are unsymmetrically substituted: the major product is a consequence of  regioselective addition to the double bond. Upon reaction with HCl, electrophilic  addition of a proton results in the formation of the most stable intermediate carbocation,  which then reacts with Cl−, to give the observed product. 275 Chapter 8 Topic: Reaction Products  92. Predict the major product(s) of the following reaction, giving regiochemical and/or  stereochemical details as relevant.  Br2, H2O? Ans:  OH Br H + OH Br H The reaction takes place with Markovnikov regioselectivity and anti stereospecificity,  giving a racemic mixture of the halohydrin as the major product.  Topic: Reaction Products  93. Draw Fischer projection formula(s) of the major product(s) of the reaction between Z-2-methyl 3-hexene and cold, alkaline KMnO4.  Ans: CH(CH3)2 CH(CH3)2 cold, dil  H OH HO H KMnO4+ H OH C2H5 HO H C2H5 The reaction takes place with syn stereospecificity, giving a racemic mixture of the diol  product.  Topic: Reaction Products  94. Draw Fischer projection formula(s) of the major product(s) of the reaction between Z-3-methyl 3-hexene and cold, alkaline KMnO4.  Ans: CH2CH3 CH2CH3 cold, dil  H3C OH HO CH3 KMnO4+ H H OH C2H5 HO C2H5 The reaction takes place with syn stereospecificity, giving a racemic mixture of the diol  product. 276 Chapter 8 Topic: Reaction Products  95. Draw Fischer projection formulas of the major product of the reaction between E-2-methyl-3- hexene and aqueous Br2.  Ans: CH(CH3)2 CH(CH3)2 CH(CH3)2 CH(CH3)2 Br2 HO H H OH H Br Br H H OH + + + Br H2O C2H5 Br H C2H5 HO H C2H5 H C2H5 The reaction takes place with anti stereospecificity. Since the alkene is symmetrically  substituted, Markovnikov rule is not applicable, and the reaction is not regioselective.  The product mixture would therefore consist of 2 pairs of enantiomers, that are  constitutional isomers of each other.  Topic: Reaction Products  96. Give a mechanistic explanation for the formation of the following product in significant yield.  What other product(s) might also be obtained? Explain clearly.   


What is the structure of the alkene?



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HI I Ans: H+ + + fast I− I

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+ I I− 

The regioselective addition of a proton first generates a secondary carbocation, which  can undergo rearrangement to a more stable 3o carbocation by two alternate pathways.  One pathway results in ring expansion to a more stable 5-membered ring. This pathway  is thus more likely, which would then lead to the observed product. The other pathway  is less likely, since ring strain is not relieved; however, this could lead to a minor  product, as shown above. 277 Chapter 8 Topic: Structure Elucidation  97. Deduce the structure of an unknown compound A, C8H16, from the following data. Briefly, but  clearly explain your rationale. A decolorizes Br2/CCl4, and upon reaction with excess H2/Ni,  affords 1-ethyl-2-methylcyclopentane. When A is subjected to ozonolysis, the following  product is obtained.  O O   Ans: A must be 3-ethyl-4-methylcyclopentene. This given data can be explained as shown  below:  C8H14: Index of Hydrogen Deficiency of A = 2 decolorizes Br2,CCl4: A must contain pi bonds A ozonolysis O O H2, Ni O O A must contain some the same carbon  skeleton and one pi bond pi bond position in A deduced from the  structure of the ozonolysis product Topic: Reaction Products  98. Predict the product(s) of the oxidation of 2,3,4-trimethyl-1,5-heptadiene with hot, alkaline  KMnO4.  Ans:  CO2 + H2O + + hot, alkaline OH KMnO4278 OO OH O Chapter 8 Topic: Reaction Products  99. Predict the structure of product obtained when cis-2-hexene is allowed to react with Zn/CH2I2.  Ans: Zn, CH2I2 H H H H + The Zn/CH2I2 produces a carbene which reacts with the alkene to give the  corresponding cyclopropane derivative. The reaction proceeds with retention of alkene  stereochemistry, resulting in a racemic mixture of the two cis enantiomers.  Topic: Reaction Products  100. Predict the structure of product obtained when 1-hexyne is allowed to react with aqueous  H2SO4 in the presence of catalytic amounts of HgSO4.  Ans: HgSO4,  H2SO4, H2O OH O The reaction of 1-hexyne with aqueous H2SO4, in the presence of catalytic amounts of  HgSO4, results in regioselective hydration to produce an enol, which tautomerizes to the  more stable keto form. 279 Department of Chemistry SUNY/Oneonta Chem 221 - Organic Chemistry I Examination #4 - December 9, 2002 ANSWERS INSTRUCTIONS —  This examination is in multiple choice format; the questions are in this Exam Booklet and the answers should be placed on the "Test Scoring Answer Sheet" which must be turned in and will be machine graded.     On the Test Scoring Answer Sheet, using a soft pencil, enter the following data (in the appropriate places): your name, instructor's name, your student (or Social Security) number, course number (30022101) and the test number (04). Darken the appropriate bubbles under the entries (do not darken a bubble under the letter in your student number), making dark black marks which fill the bubbles.  You may use a set of molecular models, but no other aids, during the exam. Answer all questions; they are worth 3.33 points each. You have 50 minutes. Good luck!  Answers are highlighted in red. Explanations are in red type.December 9, 2002 Chem 221 - Exam #4 Page 2 of 8 In questions 1-5 select the mechanism(s) [there may be more than one] that fit(s) the description provided, from the list of mechanisms below. The substrate would be an alkyl halide or tosylate. List of mechanisms: (A) SN1, (B) SN2, (C) E1, (D) E2, (E) SN1 & SN2, (F) E1 & E2,  (G) SN1 & E1, (H) SN2 & E2 1. This reaction mechanism is characterized by inversion of stereochemistry at a stereogenic reaction center and exhibits second-order kinetics. (B) 2. This reaction mechanism is characterized by partial or complete racemization at a stereogenic reaction center and exhibits first-order kinetics. (A) 3. This reaction mechanism is characterized by a carbocation intermediate. (G) 4. This reaction mechanism is characterized by the requirement that the leaving group and a hydrogen on an adjacent carbon be periplanar and preferably anti-periplanar. (D) 5. These mechanisms will both operate if a 2o substrate is reacted with a high concentration of strong base/nucleophile. (H) Secondary substrates can react by SN1, E1, SN2, and E2 mechanisms. The rates of the SN1 and E1 mechanisms are, for the most part, unaffected by base/nucleophile aggressiveness or concentration. Their rates depend on how fast the substrate forms a carbocation and the base/nucleophile is not involved in this rate limiting step. On the other hand, the rates of the SN2 and E2 mechanisms will be increased by higher concentrations of base/nucleophile and by a more aggressive base/nucleophile because the base/nucleophile is involved in the rate limiting step. So, in the presence of a high concentration of a strong base/nucleophile the SN2 and E2 mechanisms are speeded up, but the SN1 and E1 are not and, so, for the most part lose out. 6. What would be the major product(s) that would form from reaction of (S)-2-bromohexane with acetate ion at room temperature if the reaction exhibits second order kinetics?O CH3CO H I II O H OCCH3 III IV V December 9, 2002 Chem 221 - Exam #4 Page 3 of 8 (A) I, (B) II, (C) III, (D) IV, (E) V, (F) I&II; racemic mixture, (G) I&II; unequal amounts, (H) III, IV&V; III > IV > V, (I) III, IV&V; V > III > IV SN2 means inversion of configuration at the site of attack on the substrate. 7. Rank the following substrates in order of decreasing reactivity in an SN2 reaction (most reactive first, least reactive last). (I) (CH3)3C-Br, (II) CH3Br, (III) CH3CH2Cl, (IV) CH3CH2Br (A) I > II > III > IV, (B) IV > I > II > III, (C) IV > III > II > I, (D) I > IV > II > I, (E) II > IV > III > I Steric effect. 8. Rank the following substrates in order of decreasing reactivity in an SN1 reaction (most reactive first, least reactive last). [Note: C6H5 represents the phenyl group, ie a benzene ring.] (I) CH3Br, (II) C6H5(CH3)2CBr, (III) (CH3)3CBr, (IV) (C2H5)2CHBr, (V) C2H5Br (A) I > II > III > IV > V, (B) I > V > IV > III > II, (C) II > III > IV > V > I (D) II > III > IV > I > V, (E) None of the previous answers is correct. The rate depends on how fast the carbocation is formed; the more stable the carbocation the faster it is formed. There are two 3o carbocations here: II and III. II is more stable because it is also benzylic and is, therefore, resonance stabilized. 9. In which of the solvents listed below would the following SN2 reaction be fastest? CH3(CH2)3Br + NaN3 ! CH3(CH2)3N3 + NaBr (A) hexane, (B) methanol, CH3OH, (C) diethyl ether, (C2H5)2O, (D) acetonitrile, CH3C/N Solvents with negative ends solvate cations and leave anions less encumbered and more nucleophilic. 10. If a reaction proceeds through an SN1 mechanism and the concentrations of both the substrate and base are doubled, the reaction rate will (A) remain the same. (B) double. (C) triple. (D) quadruple.  (E) None of the previous answers is correct SN1 rate = k1[substrate]; nucleophile/base concentration doesn’t affect rate. 11. (CH3)3C-Br + H-C/C–Na+ )))))))))> major product(s)December 9, 2002 Chem 221 - Exam #4 Page 4 of 8 (A) (CH3)3C-C/C-H + NaBr, (B) (CH3)2C=CH2 + H-C/C-H + NaBr,  (C) (CH3)3C–Na+ + H-C/C-Br, (D) There would be no reaction. (E) None of the above answers. (A), the substitution, only works well for 1o substrates. A 3o substrate will undergo elimination with a strong base/nucleophile like acetylide anion. 12. The structure of the transition state for the reaction of hydroxide ion with methyl iodide is best represented by (A) (B) * * _ _ HO CH3 I HO CH3 I (C) (D)HO CH3 I HO CH3 I The following two questions consist of a statement followed by the connecting word because followed by a reason: <statement> because <reason>. In each question choose the correct description of the statement and the reason from the list below: (A) The statement and the reason are both factually true, and the reason is the correct explanation of the statement. (B) The statement and the reason are both factually true, but the reason is not the correct explanation of the statement. (C) The statement is true and the reason is false. (D) The statement is false and the reason is true. (E) Both the statement and reason are false. 13. Reaction of a bulky base such as (CH3)3CO– K+ with secondary alkyl halides gives predominantly E2 elimination rather than SN2 substitution because the transition state for SN2 reaction is more sterically hindered than that for E2 reaction. (A) December 9, 2002 Chem 221 - Exam #4 Page 5 of 8 14. SN2 reactions of the type RBr + NaOH ! ROH + Na+ Br– generally go slower in a solvent like dimethyl sulfoxide (DMSO) than in a solvent like ethanol because dimethyl sulfoxide can solvate cations well but cannot solvate anions very well. (D) 15. Consider the two E2 eliminations shown in the figure to the right.  From the list of answers below, select the answer which best describes how much of each of the listed compounds, I-IV, would form. (a) I-IV would form in approximately equal amounts. (b) I-IV would form, but there would be H C6H5 CH3 C6H5 CH3 H3C C6H5 H C6H5 C6H5 H H C6H5 Br I II H C6H5 H C6H5 H C6H5 H C6H5 H H C6H5 C6H5 H Br III IV


What compound would yield an equimolar mixture of CH3CH2CH2CHO and CH3CHO upon treatment with O3, followed by Zn/HOAc?



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We also discuss several other topics like any model is based on making assumptions because
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more II than I and more III than IV. (c) I would form but not II. III and IV would form, with more III than IV. (d) I would form but not II. III and IV would form, with more IV than III. (e) II would form but not I. III and IV would form, with more III than IV. (f) II would form but not I. III and IV would form, with more IV than III. (g) I and II would form, with more I than II. III would form but not IV. (h)I and II would form, with more II than I. III would form but not IV. (i) I and II would form, with more I than II. IV would form but not III. (j)I and II would form, with more II than I. IV would form but not III. In the first reaction, the conformation shown is the only one that will react because in E2 the H and leaving group (Br) should be anti-periplanar. This gives I but not II. In the second reaction the conformation of the reactant shown will lead to IV, the phenyl groups cis to each other. However, there is a second conformation that can react in this case – the one obtained by rotating the rear group counterclockwise 120o. This conformation also has an H and the Br anti-periplanar and is more stable than the conformation shown because the bulky phenyl groups are also anti-periplanar to each other. [In the conformation shown, the bulky phenyl groups are syn-clinal to each other and there would be unfavorable steric interaction.] More molecules are in the conformation with the phenyl groups anti-periplanar than in the one shown. This conformation leads to III which is formed in greater quantity.December 9, 2002 Chem 221 - Exam #4 Page 6 of 8 16. In an NMR spectrum, signals arising from hydrogens and carbons that are near an electronegative element are moved (A) upfield. (B) downfield. (C) to the outfield. (D) to the infield. (E) to “The Field of Dreams.” 17. The NMR signal from a proton that has three proton neighbors, equivalent to each other but different from itself, will be split into a (A) doublet. (B) triplet. (C) quartet. (D) quintet. (E) sextet. 18. How many signals would the compound to the right give in a 13C NMR spectrum? c c a b b a (A) 1, (B) 2, (C) 3, (D) 4, (E) 5 H3C CH3 c c 19. How many signals would the compound to the right give in a proton NMR spectrum? a H3C C C H d (A) 2, (B) 3, (C) 4, (D) 5, (E) 6 For questions 20-21 consider the following compound: a b a H3C O CH2 O CH3 20. How many signals will appear in the proton NMR of this compound? (A) 1, (B) 2, (C) 3, (D) 4, (E) 5, (F) 8 21. Which protons would appear furthest downfield? (A) CH3 on left, (B) CH2, (C) CH3 on right.b c H H December 9, 2002 Chem 221 - Exam #4 Page 7 of 8 22. Match the broadband decoupled carbon-13 NMR data given below with one of the structures also shown below: Signals at the following * values (ppm downfield from TMS): 19.1, 28.0, 70.5, 129.0, 129.8, 165.8. Six signals means six different “kinds” of carbon. (A) has 5 and (B) has 3; only (C) has 6. CH2OH CH3CH2CH CHCH2CH3 (B) O CH3 (A) (C) H2C CHCOCH2CHCH3 In questions 23-25 match the proton NMR data given in the question with one of the structures shown below: O (B) (C) (A)CH3OCH2CH2C N CH3CH2CCH3 O O (D) H3C CH3 CH3CH2CHCOH Br 23. Signals at the following * values (ppm downfield from TMS): 1.08(triplet), 2.07(quintet), 4.23(triplet), 10.97(singlet). (D) A, B, and C would each give 3 signals, not 4. The singlet at 10.97 is from a carboxylic acid proton and the splitting is consistent. 24. Signals at the following * values (ppm downfield from TMS): 1.05(triplet), 2.13(singlet), 2.47(quartet). (B) A, B, and C all have methyl groups that would produce a singlet, but only B has an ethyl group that would produce the triplet/quartet pattern. 25. Signals at the following * values (ppm downfield from TMS): 2.62(triplet), 3.40(singlet), 3.62(triplet). (C) The triplet/triplet pattern here comes from the isolated -CH2-CH2- group. None of the other compounds has this. 26. Rank the following dienes in order of decreasing stability (most stable first). H2C CH CH2 CH CH2 (I) (II) H2C C CH2 (III) (IV)CH3CH CH CH CHCH3 H2C CH CH CH2 (A) I>II>III>IV, (B) IV>III>II>I, (C) III>IV>II>I, (D) II>III>IV>I III and IV are both conjugated dienes, but III is more highly substituted. Cumulated dienes (I) are known to be less stable than conjugated or isolated (II) dienes. December 9, 2002 Chem 221 - Exam #4 Page 8 of 8 27. Which of the following compounds would be formed in significant quantity in this reaction? + HCl ClCl Cl Cl Cl I II III IV V (A) I, II, III, (B) III, IV, V, (C) I, III, V, (D) II, IV Resulting from both 1,2- and 1,4- addition to the conjugated diene with H attacking both the top and bottom carbons. 28. If a reaction can proceed both under kinetic control and thermodynamic control to give different products and in a given situation it proceeds under thermodynamic control it will be the case that (A) the product that forms faster will be the major one. Kinetic control. (B) the product that is most stable will be the major one. Thermodynamic control. (C) the product that is least stable will be the major one. Can happen with kinetic control. 29. Which of the following alkenes would be good dienophiles in a Diels-Alder reaction? O O (III) (IV) (V) (I) O H2C CHCCl O (II) H2C CHCH2CH2COCH3 (A) I, II, (B) III, IV, V, (C) I, III, (D) II, IV, (E) V Electron withdrawing groups adjacent to the double bond are helpful.December 9, 2002 Chem 221 - Exam #4 Page 9 of 8 30. In the laboratory this semester you synthesized, or attempted to synthesize, endo norbornene-5,6-dicarboxylic anhydride by reacting 1,3-cyclopentadiene with maleic anhydride in a Diels-Alder reaction. Which of the compounds shown is endo norbornene-5,6-dicarboxylic anhydride? O +O O O O O O H HO O O O H H HO O O O (E) (F) (A) (B) (C) (D) H O O O H O O H O E and F are the possible Diels-Alder products. They are diastereomers and very little of the exo product (F) forms – the Alder-Stein rule. ORGANIC CHEMISTRY I – PRACTICE EXERCISE Elimination Reactions and Alkene Synthesis 1) One of the products that results when 1-bromo-2,2-dimethylcyclopentane is heated in ethanol is shown below. Give a mechanism by which it is formed and give the name of this mechanism. CH3 CH3 2) Provide the structure of the major organic product in the following reaction. CH3 NaOCH3 H Br D CH3OH 3) Provide the structure of the major organic product from following reaction. H NaOCH3 CH3 H Br CH3OH 4) Which diastereomer of 1-bromo-4-t-butylcyclohexane, the cis or the trans, undergoes elimination more rapidly when treated with sodium ethoxide? Explain your answer. 5) Provide the structure of the major organic product from the following reaction. Br KI H3C Br 6) When 1-iodo-1-methylcyclohexane is treated with NaOCH2CH3 as the base, the more highly substituted alkene product predominates. When KOC(CH3)3 is used as the base, the less highly substituted alkene predominates. Give the structures of the two products and offer an explanation. 7) Which of the following statements apply to E1 reactions of alkyl halides? Choose as many as necessary. I. Rate = k[base] II. Rate = k[base][RX] III. Rate = k[RX] IV. The reactions occur in two or more distinct steps. V. Rearrangements are sometimes seen. 8) What is Saytzeff's rule?9) What major product results when 2-bromo-2-methylbutane is treated with sodium ethoxide. 10) How many distinct alkenes can result from E2 elimination of the compound below? Give their structures and IUPAC names. I CH3 11) Give the major product and the mechanism of the following reaction. H3C H Ph Br Ph NaOCH3 CH3OH 12) Predict the most likely mechanism and the product for the reaction below. NaOCH3 H3C CH3OH H3C Cl 13) Predict the most likely mechanism and the product from the reaction between  2-chloro-2-methylpentane and sodium ethoxide in ethanol. 14) The major product which results when 2-chloro-2-methylpentane is heated in ethanol is an ether. Show and name the mechanism by which this ether forms. 15) Which of the following mechanisms feature carbocation intermediates? A) SN1 only B) SN2 only C) E1 only D) E2 only E) both SN1 and E1 16) Which mechanism(s) give(s) alkenes as the major products, Sn1, Sn2, E1, or E2? 17) Which compound produces only one alkene when treated with sodium methoxide? A) 2-chloro-2-methylpentane B) 3-chloro-3-ethylpentane C) 3-chloro-2-methylpentane D) 2-chloro-4-methylpentane E) 2-chloro-3-ethylpentane 18) When 3-iodo-3-ethylpentane is treated with sodium methoxide in methanol, the major organic product is an ______ that is generated through an ______ mechanism. A) ether, SN1 B) ether, SN2 C) ether, E1 D) alkene, E2 E) alkene, E119) Provide the structure of the major alkene product of the reaction below. H3C CH3 Br NaOH 20) Based on Saytzeff's rule, select the most stable alkene. A) 1-methylcyclohexene B) 3-methylcyclohexene C) 4-methylcyclohexene D) They are all of equal stability 21) Based on Saytzeff's rule, select the most stable alkene. A) 1,2-dimethylcyclohexene B) 1,6-dimethylcyclohexene C) cis-3,4-dimethylcyclohexene D) They are all of equal stability FOR QS. 22-24, DRAW ALL ALKENE PRODUCTS AND CIRCLE THE PREDOMINANT ONE. 22) Br CH3 NaOH acetone 23) Br CH3 (CH3)3CO K+ (CH3)3COH 24) Br Br Zn CH3COOH 25) Propose a detailed, step-by-step mechanism for the reaction shown below. CH3 CH3 OH H2SO4 D CH3 CH3 26) Draw all likely products of the following reaction and circle the product you expect to predominate. OHH2SO4 D  27) Draw all likely products of the following reaction and circle the product you expect to predominate. CH3 OH H2SO4 D 28) Which base, ammonia (NH3) or triethylamine [(CH3CH2)3N], would be more effective to use for the following conversion? Base Cl 29) Which compound would undergoe dehydrohalogenation with strong base to give the alkene shown below as the only alkene product? CH3 CH2 CHCH CH3 A) 1-chloropentane B) 2-chloropentane C) 3-chloropentane D) 1-chloro-2-methylbutane E) 1-chloro-3-methylbutane FOR SYNTHESES # 30-32 GIVE THE MISSING REAGENTS AND STRUCTURES. 30) ABC 31) ABC 32) A B C 33) Which of the following statements applies to the E2 mechanism? A) It occurs with inversion of stereochemistry. B) It occurs with racemization of stereochemistry. C) It proceeds through the more stable carbocation intermediate. D) The C-H and C-X bonds that break must be anti. E) Use of a bulky base gives the more highly substituted alkene product.ANSWERS 1) E1 mechanism with carbocation rearrangement Br CH3 ethanol CH3 1) + Br CH3 DCH3 CH3 2) H3C H CH3 rearrangement CH3 CH3 CH3 3) CH3 HOCH2CH3 CH3 + H2OCH2CH3 2) In questions 2 and 3, only the proton trans to the leaving group can eliminate. CH3   3)   D H CH3 4) Due to the presence of the bulky t-butyl group, the ring is practically locked up in the most stable conformation with the bulky group being equatorial. t-Bu H Br H t-Bu cis trans H t-Bu = t-Butyl group H Br Of the two isomers, the cis is the only one that fulfills the anticoplanar arrangement for E2, where the leaving group and adjacent proton must be anti to each other and in the same plane.t-Bu H Br H H H H H H Br H t-Bu cis trans The atoms shown in red cannot fulfill the anticoplanar requirement. Elimination is slower or not possible 5)  H3C The atoms shown in red fulfill the anticoplanar requirement for E2. Elimination is possible and fast. 6) The small, unhindered base ethoxide yields the more stable alkene (Saytzeff’s product, i.e. the more highly substituted alkene). When the bulky t-butoxide base is used, the most accessible hydrogen is removed. This results in the least highly substituted alkene (Hoffman’s product). CH3 CH3 I CH3CH2O Saytzeff's product CH3 7) III, IV, and V. H3C O CH3 CH2 Hoffman's product 8) In elimination reactions, the most highly substituted alkene predominates. 9) H CH3  H3C CH310) 1 2 345678 1 23 2 1 45678 345678 (E)-3-methyloct-2-ene (Z)-3-methyloct-2-ene 345678 2 1 1 (Z)-3-methyloct-3-ene (E)-3-methyloct-3-ene 234567 2-Ethylheptene 11) E2. The molecule must rotate around the central cabon-carbon bond to aquire the anticoplanar arrangement required for E2. This is a stereospecific reaction that results in formation of the product where the phenyl groups are cis to each other. H3C H Ph Ph 12) Strong base and bulky substrate favor E2. Only carbon 6 has protons trans to the leaving group. The pi bond can only form between carbons 1 and 6. Can you name the product by IUPAC rules? 345 NaOCH3 2 1 6 H H3C CH3OH H3C H3C Cl H H3C 13) Strong base and bulky substrate favor E2 with preferential formation of Saytzeff’s product. NaOCH2CH3 Cl CH3CH2OH14) Weak nucleophile (ethanol, the solvent) and bulky substrate favor Sn1 as shown below. Can you tell which is the rate-determining step? Can you tell what type of reaction is involved in the last step? CH3CH2OH 1) + Cl Cl D 2) + HOCH2CH3 O H 3)+ CH3CH2OH2 + HOCH2CH3 O O H 15) E 16) E1 and E2 17) B 18) D 19) The reacton is E2. See question 12 for a similar case. ether H3C CH3 20) A 21) A 22) CH3 CH2 +   23) CH3 CH2 +  H3C CH3 Br NaOH 24)   25) First step is protonation of the alcohol by the strong acid to form a potential water molecule as a leaving group. Next is departure of the leaving group with formation of a carbocation. Next is a carbocation rearrangement from secondary to tertiary. The last step is an elimination step where the water abstracts the acidic proton next to the positive charge to form the alkene. O 1) OH OH2 + H O S OH O + HSO4 2) + H2O OH2   3) HSO4 4) + H3O+ or H2SO4 or H2O H   26)   27)   28) Triethylamine. Amines can be nucleophiles or bases. Increasing their steric bulk near the nitrogen atom diminishes their nucleophilicity while retaining the basicity. Since the substrate is sterically accessible to nucleophilic attack, a bulky base is needed to promote elimination.29) C 30) This is a typical example of a simple, multistep synthesis (in this case only two steps). This tests your ability to use previously learned reactions (e.g. from ch. 4) to design a synthesis towards a particular product, in this case cyclopentene. The last step is an elimination reaction. Any strong base combination will serve the same purpose as NaOH and acetone. Br Br2 hv NaOH acetone A B C 31) Similar to the previous problem, but this time Hoffman’s product is desired. A bulky base must be used in the last step, such as t-butoxide ion. Br2 hnBr t-BuO t-BuOH A B C Hoffman's product 32) Same as above, but this time Sayteff’s product is desired. A small base must be used in the last step. Br2 hnBr NaOH acetone Saytzeff's product 33) DA B C Practice Problems on SN1, SN2, E1 & E2 - Answers 1. Describe the following chemical reactions as SN1, SN2, E1 & E2. Draw a curved  arrow mechanism for each reaction. KCN Cl Br DMSO CN NaOH H2O, heat SN2 E2 H I Br H2O OH I CH3CH2O Na+ ethanol NaSH DMSO H SH KOH SN1 E2 SN2 SN2 Br HO DMSO NaNH2 E2 TsO TsO O OTs O CH3 CH3 NH3 NH3 H2N I NaI acetone O O CH3 CH3 SN1 SN22. For each of the chemical substitution reactions below identify the major products  and whether the reaction is likely an SN1 or SN2. O Br Br NaCN ethanol-water CH3OH / H2O O OH CN SN2 + SN1OCH3 Cl NaI (1 equiv.) acetone Cl Br CH3CH2OH 25oC ISN2 Cl O SN1 3. For each of the following compounds provide appropriate reactants and solvent  systems to synthesize them by a substitution reaction. Show which type of  substitution: SN1 or SN2. Br SN2 Br NaCN NH2 NH3 SN1 acetone Br HBr SN1 CN OH H H NaSH SN2 Br SH DMSO 10/28/13 Practice Problems for Chapters 7 and 8. To be completed after completion of  the problems in the text. 1) Draw structures for the two products and explain how they are formed.  How might you enhance the yield of B? SS S Br Br S S Br+ C4H8S2 + C6H12S2Br2 Br S A B 2) Devise SN2 reactions that would give the following products starting with  your choice of alky halides. N3CNO BrNaN3, DMSON3 Cl NaCN, DMSO CN NaH OH Br O 3) Predict the major substitution product of the following reactions and  determine if they are formed from SN1 or SN2 pathways. N + I Br I- + H3C H I CH3 Acetone HMPA H2O N I CH3 H3C OH SN2 SN2 SN1 H3C H CN SN1 I CH3 Acetonitrile CH3 H3C CNor No Rxn Br H2O EtOH MeOH OH OMe OEt SN1 10/28/13 4) For the following dibromo alkane determine which position will react  faster (be more reactive) under SN1 and SN2 conditions. Explain your  answer. Br Br 3° fastest under SN1 because carbocation 1° fastes under SN2 because unhindered 5) Predict the major elimination product of the following reactions and  indicate if they are from E1 or E2 pathways. Br I I NaOH H2O NaOMe MeOH tBuOK DMSO E2 E2 E2 DBU Cl 3 eq. NaNH2 NH3 Br Br   E2 C E2 C 6) Predict the major product in each of the following reactions and indicate  if it came from an SN1, SN2, E1, or E2 reaction. H Br NaOMe MeOH tBuOK E2 E2 H3C Br CH3 H2O H3C CH3 OH SN1 H Br H I DMSO H2O EtOH H3C Br OHSN1 CH3 NaOMe MeOH CH3 CH3 E210/28/13 7) For each of the following reactions, provide the appropriate reagents or products in the  boxes provided. C C CN Br Br NaCN Cl O OO NaO O + Br O+ NaBr 8) Answer the following questions for the reaction coordinate diagram shown below. A. Give the letter(s) corresponding to the transition state(s). ___B,D____ B. Give the letter(s) corresponding to the reactive intermediate(s). __C___ B C. Step 1 or Step 2 is the rate determining step. (circle one) D D. Step 1 is endothermic or exothermic. (circle one) E. Step 2 is endothermic or exothermic. (circle one) Energy A C E F. The overall reaction is endothermic or exothermic. (circle one) Chapter 11—Homework and practice questions Reactions of Alkyl Halides: Nucleophilic Substitutions and Eliminations SHORT ANSWER Exhibit 11-1 Circle your response in each set below. 1. Circle the least reactive compound in an SN2 reaction. ANS: 2. Circle the best leaving group in an elimination reaction. ANS: 3. Circle the best nucleophile in a substitution reaction at a primary carbon. ANS:1 Reactions of Alkyl Halides: Nucleophilic Substitutions and Eliminations 4. Circle the least reactive compound in an SN1 reaction. ANS: 5. Circle the best solvent for an SN2 reaction. ANS: Exhibit 11-2 Consider the pair of reactions below to answer the following question(s). a. or b. 6. Refer to Exhibit 11-2. a. Which reaction would be predicted to be faster? b. Explain your answer to the question in part a. ANS: a. b b. −SH is a better nucleophile than −OH because nucleophilicity usually increases in going  down a column of the periodic table and sulfur is below oxygen in group 6A. 7. How do you define a chiral carbon?2 Chapter 11 8. Refer to Exhibit 11-2. The mechanism for these reactions is: a. SN1 b. SN2 c. E1 d. E2 ANS: b Exhibit 11-3 Consider the pair of reactions below to answer the following question(s). a. or b. 9. Refer to Exhibit 11-3. a. Which reaction above is faster? b. Explain your answer to the question in part a. ANS: a. a b. The conversion of tert-butyl chloride to tert-butyl alcohol proceeds faster in 70% H2O/30%  CH3OH than in 50% H2O/50% acetone because SN1 reactions are faster in more polar  solvents. Acetone (dielectric polarization, P = 20.7) is less polar than CH3OH (P =  33.6), and the percentage of H2O is higher in the water/methanol system. 10. The original question has been combined with question #9 as part b. This placeholder  question is here to maintain the integrity of the numbering system between the printed copy  and ExamView. Therefore, it has been marked "do not use on test" in ExamView's question  information dialog. As a result, this placeholder question is automatically prevented from  being chosen as a test question. ANS: Answer not provided. 11. Refer to Exhibit 11-3. The kinetics of these reactions are: a. second-order b. first-order in nucleophile3 Reactions of Alkyl Halides: Nucleophilic Substitutions and Eliminations c. not measurable d. first-order in alkyl halide ANS: d Exhibit 11-4 Consider the pair of reactions below to answer the following question(s). a. or b. 12. Refer to Exhibit 11-4. The alkyl bromide starting materials in these reactions are classified  as: a. 3° b. 2° c. 1° d. 4° ANS: c 13. Refer to Exhibit 11-4. The solvent in these reactions is: a. nonpolar aprotic b. polar aprotic c. polar protic d. nonpolar protic ANS: b 14. Refer to Exhibit 11-4. The nucleophile in these reactions is: a. K+ b. alkyl group c. Br− d. I− ANS: d4 Chapter 11 15. Refer to Exhibit 11-4. Which reaction is faster? ANS: b 16. Refer to Exhibit 11-4. The mechanism for these reactions is: a. SN2 b. E2 c. SN1 d. E1 ANS: a Exhibit 11-5 Consider the pair of reactions below to answer the following question(s). a. or b. 17. Refer to Exhibit 11-5. a. Which reaction above is faster? b. Explain your answer to the question in part a. ANS: a. b b. Tosylate anion is a better leaving group than amide ion; tosylate is the weak conjugate base of  a strong acid, while amide is the strong conjugate base of a weak acid. 18. The original question has been combined with question #17 as part b. This placeholder  question is here to maintain the integrity of the numbering system between the printed copy  and ExamView. Therefore, it has been marked "do not use on test" in ExamView's question  information dialog. As a result, this placeholder question is automatically prevented from  being chosen as a test question. ANS: Answer not provided.5 Reactions of Alkyl Halides: Nucleophilic Substitutions and Eliminations 19. Refer to Exhibit 11-5. Doubling the concentration of potassium hydroxide in these reactions: a. causes the reaction mechanism to change b. halves the rate of reaction c. has no effect on the rate of reaction d. doubles the rate of reaction ANS: d 20. Refer to Exhibit 11-5. The mechanism for these reactions is: a. SN2 b. E2 c. SN1 d. E1 ANS: b Exhibit 11-6 Consider the reaction below to answer the following question(s). 21. Refer to Exhibit 11-6. The substrate in the reaction is: ANS: A 22. Refer to Exhibit 11-6. Compound B is the: a. SN2 product b. SN1 product c. E2 product d. E1 product ANS: b 23. Refer to Exhibit 11-6. Compound C is the:6 Chapter 11 a. SN2 product b. SN1 product c. E2 product d. E1 product ANS: d 24. Refer to Exhibit 11-6. Write the complete reaction mechanism for the formation of  Compound C in this reaction. ANS: Exhibit 11-7 To answer the following question(s) consider the data below: Reaction of bromomethane with sodium hydroxide in water forms methanol. If sodium iodide is  added to the reaction mixture, the rate of methanol formation is dramatically increased (i.e. sodium  iodide is a catalyst). 25. Refer to Exhibit 11-7. The mechanism involved in the reaction of CH3Br and NaOH is: a. SN1 b. SN2 c. E1 d. E2 ANS: b 26. Refer to Exhibit 11-7. Write a reaction pathway that accounts for the effect of added NaI. ANS: 27. Refer to Exhibit 11-7. Draw a reaction energy diagram showing the two different reaction  pathways (i.e. catalyzed and uncatalyzed). Indicate structures for all energy minima in the  diagram.7 Reactions of Alkyl Halides: Nucleophilic Substitutions and Eliminations ANS: 28. Refer to Exhibit 11-7. Explain why adding NaI increases the reaction rate. ANS: Iodide is a better nucleophile than hydroxide so we expect reaction between CH3Br and iodide to  proceed faster than the reaction between CH3Br and hydroxide. CH3I is a more reactive alkyl  halide than CH3Br because iodide is a better leaving group than bromide so when CH3I forms it  reacts with hydroxide faster than CH3Br to form CH3OH. The overall result is faster formation of  CH3OH from CH3Br when NaI is added. 29. Refer to Exhibit 11-7. Would you expect the same catalytic effect on this reaction if you  added NaCl instead? Explain your answer. ANS: No. Chloride ion is a poorer nucleophile as well as a poorer leaving group than bromide ion. Exhibit 11-8 Consider the reaction below to answer the following question(s):8 Chapter 11 30. Refer to Exhibit 11-8. Write the product that results from the electron flow in the reaction,  clearly indicating any stereochemistry. ANS: 31. Refer to Exhibit 11-8. Draw a Newman projection of the reactive conformation of the  starting material. ANS: 32. Refer to Exhibit 11-8. The mechanism of this reaction is: a. SN1 b. SN2 c. E1 d. E2 ANS: d Exhibit 11-9 Consider the reaction below to answer the following question(s).9 Reactions of Alkyl Halides: Nucleophilic Substitutions and Eliminations 33. Refer to Exhibit 11-9. Write the complete stepwise mechanism for this reaction. Clearly  show the formation of both products. Show all electron flow with arrows and draw all  intermediate structures. ANS: 34. Refer to Exhibit 11-9. This reaction obeys a rate law of the form: a. rate = k[RCl][CH3CH2OH] b. rate = k[RCl][H2O][CH3CH2OH] c. rate = k[RCl] d. rate = k[RCl][H2O] ANS: c Exhibit 11-10 Draw the structure of the major organic product(s) for each of the following reactions. Indicate the  stereochemistry for each reaction when appropriate. 35. ANS:10 36. ANS: 37. ANS: 38. ANS: 39. ANS:Chapter 11 11 Reactions of Alkyl Halides: Nucleophilic Substitutions and Eliminations 40. ANS: 41. ANS: 42. ANS: 43. ANS: 44. ANS:12 Chapter 11 PRACTICE QUESTIONS  Exhibit 11-11 Consider the reaction below to answer the following question(s). 45. Refer to Exhibit 11-11. List all chirality centers in the starting material by number. ANS: Carbon 2 is a chirality center. 46. Refer to Exhibit 11-11. As indicated by the carbon numbers, during the course of this  reaction the bond between the nitrogen atom and carbon 3 is broken and a bond between the  nitrogen atom and carbon 2 is formed. On the structures provided below, draw arrows  showing electron flow for the mechanism that accounts for these bonding changes. ANS: 47. Refer to Exhibit 11-11. If the absolute configuration at carbon 2 in the starting material is R,  what is the absolute configuration at carbon 2 in the product? ANS: The absolute configuration at carbon 2 in the product is S because an intramolecular SN2 reaction  occurred in the first step of the reaction to invert the configuration at that carbon.13 Reactions of Alkyl Halides: Nucleophilic Substitutions and Eliminations Exhibit 11-12 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 48. ______  ANS: b 49. ______  ANS: d 50. For the substitution reaction: Draw the structure present at the point indicated by the asterisk (*) on the following energy  diagram. Identify the reactant as R or S or neither.14 Chapter 11 ANS: The reactant is the R enantiomer. 51. For the substitution reaction: Draw the structure present at the point indicated by the asterisk (*) on the following energy  diagram.15 Reactions of Alkyl Halides: Nucleophilic Substitutions and Eliminations ANS: 52. For the elimination reaction: Draw the structure present at the point indicated by the asterisk (*) on the following energy  diagram.16 ANS: 53. For the elimination reaction: Draw the structure present at the point indicated by the asterisk (*) on the following energy  diagram ANS:Chapter 11 17
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