1. (6points)Writethetermthatchemistsusetodescribethetypeofcarbocationstabilizationshownforthefollowingexamples:

2. (8points)Oneofthefollowingstructuresundergoesacetolysis1011timesfasterthantheother.

a) Whichoneisfasterandwhy?(4points)

b) What stereochemistry would you expect in the products fromA? Briefly explain youranswer.(2points)

c) What stereochemistry would you expect in the products from B? Briefly explain youranswer.(2points)

4. (29points)a) Writeamechanismforthehydrolysisoftheacetalfollowingaspecificacid-catalyzedroute.

Showallarrowpushing.(10points)

b) Now write a general acid-catalyzed mechanism for the same reaction. Show all arrow

pushing.(10points)

c) Thehydrolysisofthefollowingthreestructureseithershowspecificacid,generalacid,ornocatalysis. Predict which corresponds to each mechanistic alternative and explain youranswer.(9points)

5. (13points)a) ForanE2reaction,drawthetwodifferentalkylbromideregioisomersthatwouldgivethe

followingproduct.Don’tyetworryaboutshowingstereochemistry.(4points)

b) Drawallthepossiblealkeneregioisomersthatcanbeproducedfromthetworeactantsyougave inpart“a”.Circle theregioisomer thatdominatesandtelluswhichruleyouusedtomaketheprediction.(5points)

c) Now, considering the appropriate stereochemistry, draw the possible alkyl bromidestereoisomersthatwillgivethedesiredalkenefrompart“a”.(4points)

1 2

1

2

7. (10points)Predictthepreferentialfaceofnucleophilicattacktothecarbonylcarbonusingthefollowingmodels.a) Draw the preferential alcohol products of the nucleophilic addition using the Grignard

reagents.b) Usingthetemplategiven,drawaNewmanprojectiontosupportyouranswer.

A. FelkinAhnModel

B. CramModel

9. (8points)Thefollowingtworeactionsareallowed.Labelthetwocomponentsappropriatelyto

showthattheyobeytheWoodward-Hoffmanrules(i.e.ơ2a,orthelike).a)

b)

6.(16pts)Forthefollowingeliminationreaction:

a)FillinthecornersandaxesontheMoreO’Ferrall-Jencksplotbelow(4pts):

b)WhatistheeffectofhavingabetterleavinggrouponthepositionoftheTSintheE2pathway?Whydoesthismakesense?(2pts)

S

O

LGB

S

OBH LG

S

O

LGB

S

OBH LG

Supposetheplotoflogkvs.pKaBH+oftheabovereactiongaveaslopeofzero.

c) Whatistheextentofdeprotonationoccurringatthetransitionstateoftherate-determiningstep?(2pts)

log k

pKa BH+

slope = 0

d) Whatdoestheslopeindicateaboutthetypeofbasecatalysisofthereaction?(2pts)

e) Whichreactionmechanism,E1,E2,orE1CBwouldgiveaslopeofzeroandkineticdependenceuponthebaseinasmuchasitonlysetsthesolution’spH?(2pts)

However,whentheexperimentisactuallyperformed,aplotoflogkvs.pKaBH+doesnotgiveaslopeofzero.Instead,β=0.47,asshownbelow:

f) Whateffectdoesusingastrongerbasehaveontheextentofdeprotonationatthetransitionstateoftherate-determiningstep?(2pts)

g) Whateffectdoesusingastrongerbasehaveontherateoftheeliminationreaction?(2pts)

8.(6pts,2each)Namethefollowingcyclizationreactionswiththeappropriateprefixes(number-endo/exo)andsuffices(dig,trig,tet)anduseBaldwin’stabletodeterminewhetherornoteachreactionisfavored.

a)

b)

NH2

O

N

HNN

O

OOH3O+

NNH

Br

c)

10.(8pts,2each)Usefrontiermolecularorbitaltheory(FMOT)tofillintheorbitalsforthereactionsbelow.Indicatewhetherthereactionisallowedorforbiddeninthegeometryshown.

HO

HH

O

H

H

OH OHH3O+

LUMO

HOMO

LUMO

HOMO

11.(8pts,4each)Forthefollowingelectrocyclicringopeningreactionsfillintheorbitalsbelowthatmakethereactionallowed.Describetheorbitalmovementsasconrotatoryordisrotatoryforeachreaction.Finally,drawtheallowedproductwithcorrectstereochemistry

LUMO

HOMO

LUMO

HOMO

H3CCH3

CH3

CH3

12.(8pts)Thecyclopropylringshownbelowcan“walk”aroundthecyclohexyldieneringbyaseriesof[1,5]sigmatropicshifts.

a) Drawthefrontiermolecularorbitalsthatcontrolthesigmatropicshiftshownabove.(4pts)

b) DeterminetheorientationofAandBaftertheshownsigmatropicshift,andfillintheappropriatelettersontheproductstructureabove.(2pts)

AB

[1,5]

c) Istheresultfrompartbsurprising?Whyorwhynot?(2pts)

13.(11pts)

a) WritethenameofthelabeledtransitionsnexttoeachnumbershownonthefollowingJablonskidiagram(6pts):

Acertainfluorophoregavethefollowingabsorbanceandfluorescencespectra:

b) IndicatetheStokes’shiftontheaboveabsorption/emissionspectrum.(1pt)

c) UsingonlyS0andS1,drawaJablonskidiagrambelowthatshowsthetransitionsthatgiverisetothedifferentabsorptionandemissionmaxima.Labelyourdiagramwith“absorption”and“emission”.(4pts)

3.(9pts)SN1solvolysisofthis13Cisotopicallylabeledallylderivativeresultsinscramblingofthestartingmaterial.

a) Drawthestep(s)inthesolvolysisthatlead(s)to13Cscrambling.(2pts)

b) ExplainwhyitisobservedthatextentofscramblingisNOTdependentontheconcentrationofanyaddedsodiumacetate.(2pts)

Iftheoxygenis18Oisotopicallylabeled,thenthestartingmaterialcanbescrambledasfollows:

c) Drawthestep(s)inthesolvolysisthatlead(s)to18Oscrambling.(3pts)

O

O *O

O*

O

O*O

O

O

O**O

O*

* **

*

d) Whichisotopicscramblingwouldyoupredictoccursfaster?(2pts)