ALKENES AND ALKYNES REACTIONS A STUDENT WHO HAS MASTERED THE MATERIAL IN THIS SECTION SHOULD BE ABLE TO:

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1 ALKENES AND ALKYNES REACTINS A STUDENT W AS MASTERED TE MATERIAL IN TIS SECTIN SULD BE ABLE T: 1. Given the starting materials and reaction conditions, predict the products of the following reactions of alkenes and alkynes. Markovnikov addition of acids to alkenes and alkynes, including the acid-catalyzed addition of water (hydration). Rearrangement is possible in the additions to alkenes; tautomerization occurs in the hydration of alkynes. Anti-Markovnikov addition of. Addition of halogens (and halohydrin formation). These reactions are anti additions. In halohydrin formation, the goes to the more substituted carbon. Epoxidation, and the hydrolysis of the resulting epoxides to glycols (overall anti addition). Glycol formation using either KMn 4 (cold) or s 4 (these are syn additions). Degradation of alkenes and alkynes using either ozonolysis or KMn 4 (hot) Addition of carbenes to alkenes 2. Using any of the above reactions, propose syntheses of compounds that can be made using alkenes as starting materials or intermediates. As always, synthesis problems may require any reaction that you have studied in the course so far. 3. Propose mechanisms, and predict and explain experimental results using your knowledge of mechanism. Important reactions include: Markovnikov additions (which proceed by protonation of the alkene to give a carbocation). Addition of bromine and bromohydrin formation (by formation of the bromonium ion). ydrolysis of epoxides (under acid conditions the oxygen is protonated first). 4. Identify unknown alkenes and alkynes when given either the products of ozonolysis or of KMn 4 degradation. You will not be called on to distinguish between cis and trans isomers; these methods do not give that information. (Further information can be obtained from the index of hydrogen deficiency). 5. Use the results of simple chemical tests in identifying unknown compounds. Data from IR spectra may also be used. Important tests include: Solubility in concentrated sulfuric acid (compounds containing only alkanes, halogens, and aromatic rings do not dissolve) omine in carbon tetrachloride (alkenes and alkynes give an immediate reaction, decolorizing the reddish-brown bromine solution) Potassium permanganate (cold, dilute) (alkenes and alkynes give an immediate brown precipitate; other compounds leave the permanganate solution purple) Silver nitrate in alcohol solution (gives a white precipitate with alkyl chlorides, a tan ppt. with alkyl bromides, a brown ppt. with alkyl iodides, no reaction when the halogen is attached to an sp2 carbon, and no reaction with other materials) Silver nitrate in ammonia (gives a white ppt. with terminal alkynes) 96

2 A STUDENT W AS MASTERED TE BJECTIVES N TE PREVIUS PAGE SULD BE ABLE T SLVE TE FLLWING PRBLEMS AND RELATED NES: 1.1 Predict the major organic product or products of each of the following reactions. (C 3 ) 2 CC=C 2 + Cl -----> no peroxides C 3 C 2 C 2 C=C > peroxides c) C 3 C 2 C 2 C=C > d) (cold, dilute) + KMn > e) f) KC() > CCl3 CCl > g) + Cl > h), 2, heat + KMn > > C i) C C C CCl > j) C2I2/Zn(Cu) > ether 97

3 1.2 For each of the following compounds, compare the reaction products from the addition of in the presence of peroxides with the addition of in the absence of peroxides. C C=C2 C=C2 2. Propose a synthesis of each of these compounds, from the given starting material and any needed inorganic reagent and/or solvent. from C 3 C 2 C 2 from C 3 C C c) from d) from 98

4 2.2 Propose a synthesis of each of these compounds from the given starting materials(s) and any needed inorganic reagents or solvents. from C 3 C 2 C 2 C 2 from C C and C 3 C 2 I c) (C 3 ) 3 C from (C 3 ) 2 CC 2 d) from e) C C from C C f) (C 3 ) 2 CC 2 C 2 C 3 from (C 3 ) 2 C=C 2 and -C CNa 99

5 3. Propose a mechanism for each of the reactions shown > (C 3 ) 2 CC=C 2 + Cl -----> (C 3 ) 2 CClC 2 C 3 c) C=C > C2 d) C 3 C 2 C=C I -----> C 3 C 2 C C 2 + I e) C > f) C2 3 (trace) > 100

6 4.1 Identify each of these unknowns from the information given. 3 Zn C > > 2 C- + C2C- 3 Zn C > > 2 + C2C- c) KMn4, C > heat > -C-C2C2C2C- d) KMn4, C > heat > C2C2C2C 4.2 Predict the products of the following reactions. 3 Zn ----> > 2 C2 C=C KMn4, > heat > 5.1 Match each set of test results with one of the compounds shown. C2C2C2 C2C2C C- A B C D E Decolorizes 2 in CCl 4 Soluble in 2 S 4 No reaction with AgN 3 in ammonia No reaction with cold dilute KMn 4 No reaction with AgN 3 in alcohol Soluble in conc. 2 S 4 101

7 5.1 Unknowns, continued. The possibilities are: C2C2C2 C2C2C C- A B C D E c) Gives a brown precipitate with cold dilute KMn 4 Gives a white precipitate with AgN 3 in ammonia Soluble in conc. 2 S 4 d) No reaction with cold dilute KMn 4 No reaction with alcoholic AgN 3 Insoluble in conc. 2 S Describe simple chemical tests that can distinguish between: cyclohexene and cyclohexyl bromide 1-hexene and 1-hexyne c) tert-butyl alcohol and tert-butyl bromide d) pentane and 1-pentene e) ethanol and 2-pentyne 102

8 ANSWERS T TE PRBLEMS: 1.1 Predict the major organic product or products of each of the following reactions. (C 3 ) 2 CC=C 2 + Cl -----> (C 3 ) 2 CClC 2 C 3 no peroxides C 3 C 2 C 2 C=C > C 3 C 2 C 2 CC 3 peroxides c) C 3 C 2 C 2 C=C > C 3 C 2 C 2 C 2 C 2 d) (cold, dilute) + KMn > e) KC() > CCl3 Cl Cl f) CCl > + enantiomer g) + Cl > Cl + enantiomer + Cl h), 2, heat + KMn > > C C C i) C C j) C C2I2/Zn(Cu) > ether CCl > C C C C + enantiomer 103

9 1.2 Compare the addition of in the presence and in the absence of peroxides to each of the following compounds. (int: Predict the products.) C C=C2, no peroxides ()2C C2, peroxides ()2C C2C2 Note that both of these problems involve rearrangements in the absence of peroxides., no peroxides C=C2, peroxides C2 C2C2 2.1 Synthesis problems. These answers are in shorthand (not balanced equation) form., peroxides > 2, peroxides C 3 C C > C 3 C 2 C 2 c) C65C > 2, > d) K, heat > C65C > 2, > (Last two steps as in c) above) 2.2 More synthesis: 2, light > K > heat > peroxides 104

10 NaN2 C 3 C 2 I C C > C CNa > C CC 2 C 3 and then 2, Ni 2 B C CC 2 C > 2 C=CC 2 C > C 3 C 2 C 2 C 2 peroxides 2S4, heat, no peroxides c) (C 3 ) 2 CC > (C 3 ) 2 C=C > (C 3 ) 3 C d) > light K > heat C65C > > 2 e) C C C > CCl4 C CC Li, N >, peroxides f) (C 3 ) 2 C=C > (C 3 ) 2 CC 2, then: -C CNa (C 3 ) 2 CC > (C 3 ) 2 CC 2 C C, then: 2 2, Pt (C 3 ) 2 CC 2 C C > (C 3 ) 2 CC 2 C 2 C 3 C NaN > C C then C 105

11 3) Mechanisms. Note that balanced equations are used throughout > > > > (C 3 ) 2 CC=C 2 + Cl -----> (C 3 ) 2 CClC 2 C 3 ()2CC=C2 + Cl -----> ()2CC + Cl ()2C C -----> ()2C C2 ()2C C2 + Cl -----> ()2CClC2 c) C=C > C2 C=C > C + 2 C -----> C > C2 C2 2 C > C

12 3) Mechanisms, continued. Note again that balanced equations are used throughout. d) C 3 C 2 C=C I -----> C 3 C 2 C C 2 + I e) C2C=C > C2C C2 C2C C2 C > + I -----> C2C C2 I + C > + 2 3C > 3C > + 3 f) C2 3 (trace) > C > >

13 4.1 The unknowns are: C2C=C()2 CC2 c) d) 4.2 The products are: 3 Zn ----> > 2 C + CC2C C2 C=C KMn4, > heat 5.1 The unknowns are: B; A; c) E; d) C > + C C + C2 5.2 Descriptions of simple chemical tests that can distinguish between the pairs. (nly one answer is required.) Cyclohexene gives no reaction with alcoholic AgN 3, while cyclohexyl bromide gives a white precipitate. Cyclohexene reacts with bromine in carbon tetrachloride and with cold dilute potassium permanganate, and dissolves in concentrated sulfuric acid; cyclohexyl bromide does none of these things. 1-exene gives no reaction with AgN 3 in ammonia, while 1-hexyne gives a white precipitate. c) tert-butyl alcohol dissolves in concentrated sulfuric acid, while tert-butyl bromide does not. The bromide gives a white precipitate with AgN 3 in alcohol, while the tert-butyl alcohol does not react. d) 1-Pentene decolorizes bromine in carbon tetrachloride, gives a brown precipitate with cold dilute potassium permanganate, and dissolves in conc. sulfuric acid. Pentane does not react with any of these reagents. e) 2-Pentyne reacts with bromine in carbon tetrachloride and with cold dilute potassium permanganate; ethanol does neither of these things. 108

14 Name Eighth Drill Test (Sample) rganic Chemistry 2210 DR Answer All Questions 1) Predict the major organic product or products the following reaction. C 3 C 2 C 2 C=C 2 + C 6 5 C > 2) Propose a synthesis of each of the following compounds from the given starting material and any needed inorganic reagents or solvents. from from c) (C 3 ) 3 C from (C 3 ) 2 CC 2 3) Propose a mechanism for each of the reactions shown. 3 + C 3 C 2 C=C > C 3 C 2 CC Cl ----> + Cl 4) Give the structures of these unknowns from the information given. C816 3 Zn, > > 2 C2C2C- C814 KMn4, base, heat acid > > + C2 5) Which of these compounds gives a peak in the IR spectrum near 1640 cm-1, is soluble in conc. 2 S 4, reacts with cold alkaline KMn 4, and gives no reaction with either silver nitrate in ethanol or Ag(N 3 ) 2 +? A. C 3 C=C 2 B. C 3 C C- C. C 3 C 2 C 3 D. C 3 C 2 E. C 3 C 2 Cl 109

15 Name Eighth Drill Test (Sample B) rganic Chemistry 2210 DR Answer All Questions 1) Predict the major organic product of each of the following reactions. C=C S > + peroxides > 2) Propose a synthesis of each. You may use any needed inorganic reagents and solvents. (C 3 ) 3 CCl from (C 3 ) 3 C bicyclo[3.1.0]hexane from cyclopentene c) trans-1,2-cyclohexanediol from bromocyclohexane 3) Propose a mechanism for each of the reactions shown. For problem, first complete the equation by predicting the product > C=C Cl > CClC2 + 4) Which of the compounds shown is soluble in conc. 2 S 4, reacts with cold alkaline KMn 4, and gives no reaction with either AgN 3 in alcohol or Ag(N 3 ) 2 +? A. C 3 C 2 B. C 3 C 2 C. C 3 C=C 2 D. C 3 C C- E. C 3 C 2 C 3 5) Give the structures of the unknowns from the information given. KMn4, base, heat acid C > > 3 Zn, 2 C > > + 110