CHEM 237-Davis Organic Chemistry Examination 3 April 15, Instructions

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1 CHEM 237-Davis rganic Chemistry Examination 3 April 15, 2009 YUR NAME (Last, First) Initial of Last Name Instructions Fill in your name in the space above and on the next page Print the initial of your last name in the box above Please sign the Honor Code acknowledgment on the following page D NT PEN THIS EXAM UNTIL INSTRUCTED T D S Answer questions in the spaces provided 1

2 CHEM 237-Davis, Examination 3 YUR NAME (Last, First) University Honor Code Acknowledgment I have neither given nor received assistance in taking this examination. Signature This exam is worth 125 points Notes There are 6 Sections on pages Make sure your exam has all the pages. Nothing written on page 12 will be graded-this is for scratch work Points Problem 1 (10) Problem 2 (10) Problem 3 _ (45) Problem 4 (20) Problem 5 (20) Problem 6 (20) Total (125) EXAM BEGINS N NEXT PAGE 3 2

3 1.AbsoluteConfiguration(10pts) A)Intheleft handbox,addthenecessarysubstituentstogivethestructurefor 1 (R) iodo 3 (R) fluoro cyclohexane1.(5pts) B)Intheboxonrightdrawthelow energychairconformationfor1 (R) iodo 3 (R) fluorocyclohexane1.itisnotnecessarytodrawallthehydrogenatoms.but,youmustdrawthe hydrogenatomsatthechiralcentersbearingthesubstituents.identifyeachsubstitutentasaxial orequatorial.(5pts) 2.A)Showamechanismforreactionofcis 2,3 methylbutene1withozonetogive3.(5)

4 B)CalculateΔH o fortherearrangementof3to4.usethefollowingvaluesforbonddissociation energies:c Cσbond=90kcal/mol,C σbond=85kcal/mol, σbond=50kcal/mol, C Hσbond=95kcal/mol.(5pts) EnergyDiagrams.A)Usingcomparativereactioncoordinate/energydiagrams,andaminimum ofwords,explainwhysn2reactions(sayreactionofmethyliodidewithchlorideanion)proceed fasterinanaproticsolventratherthaninapolarproticsolvent.labelallstartingmaterials, transitionstates,intermediates(ifany)andproducts,2)labelallδg values.(10points) ΔH o = Energy Reaction Coordinate 4

5 B)Usingcomparativereactioncoordinate/energydiagrams,andaminimumofwords,explain whysn1reactionsproceedfasterfor3 o alkylhalidesthanfor1 o alkylhalides.labelallstarting materials,transitionstates,intermediates(ifany)andproducts,2)labelallδgvalues.(10points) Energy Reaction Coordinate 5

6 4.ShortAnswer(45pts). A)Circleanychiralcompound(s). B)Labelanychiralcenter(s)inthefollowingmoleculeswithanasterisk(*). H H C)Arethefollowingcompoundsenantiomers(E),diastereomers(D),mesoisomers(M)orthe same(s)?writee,d,m,orsintheblankprovided. CH NH 2 H 2 N CH 6

7 D)Circlethefollowingstatement(s)doesnotcorrectlydescribeunimolecularnucleophilic substitution(sn1)reactionsofalkylhalides?(">"means"reactsfasterthan") a) Carbocationsareintermediatesinunimolecularnucleophilicsubstitutions. b) TheorderofdecreasingreactivityasafunctionofleavinggroupisRI>RBr>RCl. c) TheorderofalkylbromidereactivityisR3CBr>R2CHBr>RCH2Br>CH3Br. d) TherateofanSN1reactiondependsontheconcentrationofthenucleophile. E) F) AssumethereactioninvolvesmolecularBr2inCCl4 7

8 G) H) 8

9 5.Hydrobrominationofindene1occursatthedoublebondinthe5 memberedringtogive2.the reactionisregiospecific,asnocompound3isformed.notethatthedoublebondsinthe 6 memberedringof1areunreactive. Br + H Br + Br % Yield 0% Yield a)drawastepwisemechanismfortheformationofcompound2fromindene1andhbr.use arrowstoindicateelectronflowandshowintermediates.(10pts). b)brieflyexplainandillustratewhythisreactionisregiospecific,givingonly2andno3.(5pts) c)basedontheaboveinformationdrawthestructureofthemajorproductformedupon hydroboration/oxidationofindene1.(5pts). 9

10 H S 6.Mechanism.Answerthefollowing2questions.(20pts). A)Thefollowingsubstitutionreactionproceedswithcompleteretentionofconfiguration.Propose amechanismforproductformationthatisconsistentwiththestereochemistry.showall intermediatesandindicateelectronflow.clearlyindicatestereochemistryofallintermediatesand products. (S) S H 2 (S) + NaBr S + NaI I H Br H B)Proposeamechanismforthistransformation.Showallintermediatesandelectronflow. H H 2 H 2 H 10

11 Blankpageforscratchwork 11