Ch6 - Chapter 6: Reactions o f Alkenes S olutions' 112 C...

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113 Solutions' Chapter 6: Reactions of Alkenes 112 CHAPTER 6 Solutions to the Problems PrQblem, 6.1 Nam~ and draw the structural fQrmula fQr the prQduct Qf each alkene additiQn reactiQn. (a) + HE> . Qm, ~ 0:' I-Bromo-l-methyl- cyclohexane O CH 3 (b) Q CH 2+ HI . I l-Iodo-l-methyl- cyclohexane Note that both alkenes give products with the halogen at the more substituted position. PrQblem 6;2 Arrange these carbQcatiQns in Qrder Qf increasing stability. 0 + + (b) (a) . CH 3 .· QCH 3 . The order of increasing stability of carbocations is methyl < primary < secondary < tertiary. Thus the three carbocations can be ranked as follows: 0 - +' . - + (b) 0 CH 3 (a) (c) CH 2 < . < OCH 3 Primary carbocation Secondary carbocation Tertiary carbocation PrQblem 6.3 PrQpQse a mechanism fQr additiQn Qf HI tQ l-methylcyclQhex~ne to give l-iodQ-I-methylcyclQhexane. Which step in YQur mechanism is rate determining? 5rep1, + ::1:' <. PH r.;:, d~~;:;'~:~:g. OCH3 A rate-determining proton transfer from HI to the carbon-carbon double bond to give a 3° carbocation intermediate. . 5rep2' < ~(' F"t • ~I. ,. L/'~H3 Reaction of thecarbocation intermediate with iodide ion completes the valence sheil of carbon and gives the product. Problem 6.4 Draw a structural fQrmula fQr the prQduct Qf each alkene hydrationreactiQn: (a) 2-Methyl-2-butanol Chapter 6: Reactions of Alkenes Solutions (b) + 2-Methyl-2-butanol Problem 6.5 PropQse a mechanism for the acid-catalyzed hydration of l-methylcyclQhexene tQ give l-methtlcyclQhexanQl. Which step in YQur mechanism is rate determining? Step 3: H H . I O '~H~ 0 ':6: 0+- Fast ;.; . + :'Q--H ------l. .... + H-(rH . CH I '. CH I 3 3 H . H PrQblem 6.6 The acid-catalyzed hyd.r~tion of 3,3-dimethyl-1 ~butene-gives 2,3-dimethyl-2-butailol as the major product. PrQpQse a mechanism for fQrmatiQn Qf this alcQhQI. ~ . + 3,3-Dimethyl-l-blltene 2,3-Dimethyl.2-butanol Step 1: Slow, rate- determining + . :O--:-H I H + Proton transfer from the acid catalyst to the alkene gives a 2° carbocation intermediate in the rate-determining step, . Fast The 2° carbocation r'earranges to the more stable 3° carbocation.
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114 Solutions Chapler 6: Reactions of Alkenes Step 3: Fast .. Step 4: ~ .. + 0:. .. ~ Fast .. ~ -- H . . + ~H + :o-H .. I H H A new chiral center is created, so the product is a racemic mixture of two enantiomers. . CH 2 .. (b) cr . + CI, Problem 6.8 Draw the structure of the chlorohydrin for.med by treating l-methylcyclohexene with CI 2 /H 2 0. CI "OH -' + " ," CH 3 Two new chiral centers are created and due to the trailS addition geometry of the reaction, the product will be a racemic mixture of the two enantiomers shown. Problem 6.9 Draw structural formulas for the alkene that gives each alcohol on hydroboration-oxidation. (i
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This note was uploaded on 07/09/2011 for the course CHE 301 taught by Professor Diver during the Spring '08 term at SUNY Buffalo.

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Ch6 - Chapter 6: Reactions o f Alkenes S olutions' 112 C...

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