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5.03FinalExam

JonasC.PetersandChristopherCummins

May21,2009

9am–12pm

Instructions:writeyournameandthatofyourTAclearlyinthelowerlefthandcornerofthisfrontpage.Readoverthetestquestionscarefullybeforewritingdownany answers.Answer all questions to thebest ofyourabilitytoreceivepartialcredit.

Problem PossiblePoints PointsEarned1 20 2 20 3 20 4 20 5 20 6 20 7 20 8 20 9 20 10 20 11 20 12 20 13 20 14 20

Total:

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1.TheperiodicTableBelowisablankperiodictable,with15boxeshighlightedbyaheavyline.Fillintheappropriateelementformulaforeachboxindicated.Twopointswillbedeductedforeveryboxisthatisnotcorrectlylabeledfromthemaximumpointsyouwouldreceiveassumingallboxeswerecorrectlylabeled.

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2.SymmetryElementsandOperationsAnswerthefollowingquestionspertainingtotheBrF5molecule,drawninFigure1withthecoordinatesystemspecified.

TheBrF5moleculedrawnwithCartesianaxesspecified.

1.WhatisthesymbolfortheprincipalaxisofrotationfortheBrF5molecule?2.Reflectionthroughthexzplaneinterchangeswhichpairoffluorineatoms?3.WhichoftheCartesianplanesisnotaσplane?4.AretherenC2axeslocated⊥totheprincipaln‐foldaxisofrotation?5.HowmanyC2axesarepresent?6.Howmanyσplanesarepresent?7.WhatisthesymbolforthesymmetryoperationthatinterchangesFawithFb?8.HowmanyoperationsarepresentthatinterchangeFbwithFd?9.Givethesymbolsfortheoperationsfrompart8ofthisproblem.

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3.PointGroups

Structurestobeconsideredaspartofproblem2.1.Assigneachofthestructuresdepictedabovetoapointgroup:

(a)_________(b)_________(c)_________(d)_________(e)_________(f)_________(g)_________(h)2.DrawthestructureandassignthepointgroupofPF5.3.Drawthestructureandassignthepointgroupofferrocene.4.Aperfectcubebelongstowhatpointgroup?

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4.HypervalentmoleculesForthisproblemwewillconsidertheSH6moleculeasamodelfortheSF6molecule.Thelatterisaknown,stablemolecule,whereasSH6isnotknownandstablebutisusefulasatheoreticalmodelbecauseithasonly10valenceatomicorbitalstotal,whiletherealsystemSF6has28.Toanswerthequestions,itwillbehelpfultorefertothefigurebelow,containingtheOhcharactertable,asisappropriatetoeitherSF6orSH6.

1.Takethesixhydrogen1satomicorbitalsofoctahedralSH6asabasisforareduciblerepresentation,ΓredandfindtheirreduciblerepresentationsthatarethecomponentsofΓred.2.Towhichoftheirreduciblerepresentationsdothevalenceorbitalsofsulfurbelong?3.Lookingatyouranswertopart1ofthisquestion,doanyoftheirreduciblerepresentationsgeneratedfromthesetofsixhydrogen1satomicorbitalsnotfindasymmetrymatchamongthesetofsulfurvalenceatomicorbitals(seepart2)?Whichone(s)?4.Atypicalline‐drawingofSF6orSH6showsthesulfurwithlinesdrawnbetweenSandeachofthesixatomstowhichSisconnected,implyingperhapsthattherearesixtwo‐electronbondsandthusatotalof12electronsinthevalenceshellofthesulfuratom,inviolationoftheoctetrule.Accordingtoyoursymmetryanalysis(parts1‐3),istherereallyaviolationoftheoctetrule?Explain,givingaspartofyourexplanationthelabelsfortheirreduciblerepresentationsofallofthesymmetry‐allowedbondsinSH6.

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5.PolyhedralBoranesandWade’sRules

Thequestionsforthisproblempertainto[B6H6]2−andtoB5H9,sketchedaboveasunlabeledlinedrawings,andwiththelattertobeconsideredinC4vpointgroupsymmetry.

1.Calculatethetotalnumberofvalenceelectronsinthe[B6H6]2−ion.2.CalculatethetotalnumberofvalenceelectronsfortheB5H9molecule.3.Howmanyelectronsaretherein[B6H6]2−forframework/clusterbonding?4.Accordingtotheacceptednomenclature,[B6H6]2−isreferredtoas“closo”.WhatisthecorrespondingtermwithreferencetoB5H9?5.ThefourbridgingHatomsinB5H9servetoreplaceanaxial[H—B]2−unitin[B6H6]2−.WhatarethethreeirreduciblerepresentationsoftheC4vpointgroupforwhichthefourbridgingHatomvalenceorbitalsinB5H9serveasabasis?Showyourwork.

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6.Whichoftheirreduciblerepresentationsfrompart5correspondstothetangentialorbitalsofthe[H—B]2−unitthathasbeenreplaced?7.Whichoftheirreduciblerepresentationsfrompart5findsnocounterpartamongthevalenceorbitalsofaH—Bunit?

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6.MLXZPlotsTofigureoutwhereaparticularorganometallicmoleculeshouldbelocatedinaMLXZplotforaparticulard‐blockelement,themoleculemustbefirstassignedtoitscorrectMLlXxZzclass.MakesuchanassignmentforeachmoleculelistedbelowandforeachmoleculegivethevalencenumberVN,theelectroncountEN,andthedncount,andindicatewhetheryouthinkthemoleculeislikelytobestableenoughtobeisolated.1.Cr(η6‐C6H6)22.(tBuO)3Mo≡CtBu

3.[PtCl3(η2‐C2H4)]‐4.Ru(η5‐C5H5)(CO)2(C2H4)5.Cp*Ni≡N—O,whereCp*=η5‐C5Me5andthebondangleatnitrogenislinear.

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7.DOrbitalsandCoordinationChemistryForthisproblemwewillutilizetheinformationprovidedintheFigurebelow.Therequestedd‐orbitalsplittingdiagramsshouldbeσ‐onlyinnature.

AngularOverlapModel(AOM)

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1.Intheboxprovided,drawinthed‐orbitalsplittingdiagramforCr(CO)6andpopulatewiththecorrectnumberofelectrons.Chromiumisingroup6.Anydegenerateorbitalsshouldbedrawninside‐by‐side.

2.Inyouranswertopart1,didyourepresentCr(CO)6ashighspin(HS)oraslowspin(LS)?Explainyourchoice.3.Basedonyouranswertopart1,howmanyunpairedelectronsdoesCr(CO)6have?4.Intheboxprovided,drawinthed‐orbitalsplittingdiagramfor[PtCl4]2−andpopulatewiththecorrectnumberofelectrons.Platinumisingroup8.Anydegenerateorbitalsshouldbedrawninside‐by‐side.

5.Gobacktoyourdiagramfrompart4ofthisquestionandlabeleachoftheorbitalsinthesplittingdiagram.Isthecomplexexpectedtohaveanyunpairedelectrons?

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6.Intheboxprovided,drawinthed‐orbitalsplittingdiagramforMoCl5andpopulatewiththecorrectnumberofelectrons.Molybdenumisingroup6.Anydegenerateorbitalsshouldbedrawninside‐by‐side.

7.Gobacktoyourdiagramfrompart6ofthisquestionandlabeleachoftheorbitalsinthesplittingdiagram.Howmanyunpairedelectronsisthecomplexexpectedtohave?

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8.MicrostatesandTanabe­Sugano1.Identifythegroundtermofthefollowinggas‐phaseions:(i)Mn2+(ii)W3+(iii)Pd2+2.WhatisthelargestMLvalueagasphase3d4ioncanhave?

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DensityFunctionalTheory(DFT)isnowfrequentlyusedtopredict/rationalizetheelectronicstructureofinorganiccomplexes.AssumeyouhaverunDFTcalculationsonthecomplexCr(H2O)63+toobtaintheLigandField(LF)parametersofΔo=17,600cm‐1andB=700cm‐1.3.Sketchad‐orbitalsplittingdiagramforCr(H2O)63+,labeleachd‐orbitalandfillintheappropriatenumberofd‐electrons,anddefinethetermΔoinyourdiagram.4.WhatisthephysicaloriginoftheBterm?5.UsetheTanabe‐SuganoDiagramprovidedbelowtodeterminetheenergyofthespin­allowedLFtransitionsyouanticipatebasedontheDFTcalculation.Showyourwork.

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9.LigandSubstitutionandelectronicstructure

(a) RankinorderofincreasingrateofsubstitutionbyH2Othefollowingcomplexes:

Complex NumericalRanking(1beingslowest)

[Cr(H2O)6]3+ [Ir(NH3)6]3+ [Co(NH3)6]2+ [Co(NH3)6]3+

(b) Thecomplex[Cr(H2O)6]2+issubstitutionallylabile,whereas[Cr(CN)6]2‐isinert.Why?

(c) Predictwhetherthefollowingcomplexesshouldbelabileorinertgiventhemagneticdataprovided(note:experimentalmomentsoftendeviatefromtheiridealspin­onlyvaluesduetospin­orbitcoupling).

Complex MagneticMoment(inBM) LabileorInert?

(i)[Cr(O)(Cl)5][NH4]2 1.82BM (ii)[MnI6][K]2 3.82BM

(iii)[Fe(CN)6][K]3 2.40BM (iv)[Fe(NH3)6][Cl]2 5.45BM Fortheanswersyouprovidedaboveprovideabriefrationalusinganelectronicstructureargument.(i)

(ii)

(iii)

(iv)

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10.LigandSubstitutionBelowistheratedatacollectedforTHFself‐exchangeforthetwosquareplanarplatinumcomplexesshown.

(a) ProvideamechanismforTHFself‐exchangeforeachcomplexthatwould

accountfortheratedata.

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Sketchyourmechanismsbelow:

(b) ThetemperaturedependenceoftherateofTHFself‐exchangeprovidesthefollowingactivationparameters:

[Ph2B(CH2PPh2)2]Pt(Me)(THF):ΔS‡=0.1entropyunits;ΔH‡=16kcal/mol

{[Ph2Si(CH2PPh2)2]Pt(Me)(THF)}+:ΔS‡=‐30.2entropyunits;ΔH‡=1.9kcal/mol

Arethemechanismsyousketchedaboveconsistentwiththeseactivationparameters?Explain.

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11.Electron­transfer

Inclasswediscussedthefactthatcertaintetra‐imineCo(II)complexeswillcatalyzethereductionofprotonstohydrogenbychromouschlorideinaqueoussolution,wherechromouschlorideisitselfthermodynamicallybutnotkineticallyabletoperformthereactionintheabsenceofthecobaltcatalyst.

1.Doyouexpectthisprotonreductionreactiontoproceedviaaninner‐sphereoranouter‐spheremechanism?Why?2.Proposeaplausibledetailedmechanismforthecobalt‐catalyzedreductionreaction.

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3.Aswasexplicitlydoneinclass,sketchapairofpotentialenergysurfacesforreactantsandproductsandillustrateonyourdiagramthephysicalmeaningofΔG‡andλ.WhatistheabsolutemagnitudeofΔG‡inunitsofλ?

4.Stateinwordswhatismeantbythe‘MarcusInvertedRegion’,andillustratethephysicaloriginoftheinvertedregionusingtwopotentialenergysurfaces,asforthecasesabove.

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12.Organometallicreactionmechanisms 1. Low temperature protonation of the palladium dibutyl complex shown below leads to a mixture of two complexes stabilized by β-agostic interactions. Propose a mechanism that accounts for the formation of species (a) & (b).

2. Provide a detailed mechanism, which consists of three fundamental steps, for the PtIICl2 catalyzed transformation shown below.

CH4 + H2O + PtIVCl6

2- → CH3OH + 2H+ + PtIICl2 + 4Cl-

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3. Murai has discovered catalytic systems for transformations such as that shown below. Sketch a detailed plausible mechanism for the representative transformation shown.

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13. Industrial homogeneous catalysis 1. Draw a reaction below that exemplifies the ‘hydroformylation reaction. 2. Draw a reaction below that exemplifies an ‘olefin metathesis’ reaction. 3. Draw a reaction below that exemplifies the ‘Wacker’ process. 4. In the Wacker process, what is the specific role of the CuCl2 additive. 5. In the Cativa process for the synthesis of acetic acid, what is the key chemical advantage of the iridium catalyst system as compared to the rhodium catalyst originally used by Monsanto?

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14. Bioinorganic chemistry Using the elementary inorganic chemistry concepts that you have learned in this course, please draft a scholarly paragraph that describes the chemical transformation/s known as ‘photosynthesis’ and how, in brief, the light reactions of photosynthesis are thought to work. In your paragraph, be sure to include the following concepts: ligand substitution, electron transfer, reorganizational energy, redox shuttling, single photon coupled to multi-electron transfer, Marcus inverted region, water oxidation.