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SolutionstoProblemsAramaticityBuildingBridgestoKnowledge

PhotoofafreewayinShanghai,China

1. UsethedatainTable9.3tocalculatetheresonancestabilizationenergyforbenzene.

2. Whichofthefollowingcompoundsarearomatic?

a. notaromaticb. notaromaticc. notaromaticd. aromatice. notaromaticf. aromaticg. notaromatich. notaromatic

Resonance Energy for Benzene = 3 ΔHhydrogenation of cyclohexene − ΔHbenzene

REB = 3 x 120 kJ/mol − 208 kJ/mol = 152 kJ/mol

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3. Namethefollowingcompounds:

Thefollowingnamesarenotexhaustiveforthesecompounds,i.e.,othernamesarealsoacceptable.

a. 3-chlorobromobenzeneorm-chlorobromobenzeneb. 1,3,5-trinitrobenzeneorpicricacidc. 3-chloroacetophenoneorm-chloroacetophenoned. 4-methylanilineorp-methylanilinee. 3-ethyltolueneorm-ethyltoluenef. 3-methoxybenzoicacidorm-methoxybenzoicacid

4. Arrangethefollowingcompoundsinorderofincreasingacidity:

f>d>a>b>c>g>e>h

5. Explainthefollowingobservations:

Benzeneisaromatic,i.e.,theelectronsinthesix“2p”parallelatomicorbitalsperpendiculartosixcoplanarcarbonatomsinteractinsuchamannerthattheresultingstructuredoesnotconsistofisolateddoublebonds,butastructurethatisstabilizedbyformingthreebondingmolecularorbitalsand3antibondingmolecularorbitals.Thisaromaticstructuredoesnotundergoadditionreactions.

+ Br2/CCl4 No Reaction

+ HBr No Reaction

+ KMnO4273 K

No Reaction

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6.AnunknownaromaticorganiccompoundC6H4Cl2upontreatmentwithHNO3/H2SO4gaveonlyoneproduct.Whatisthestructureofthearomaticcompound?

7. Drawallpossibleisomersfortrimethylphenol.

8. Suggestamechanismforthefollowinghypotheticalreactionandconstructanenergyprofilediagramforthereaction.

WhereZisacatalyst 1.

GY + Z → YZ− + G+

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2.

3.

4.

(5)

(6) HYZ➝HY+Z

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9. Usingtheinformationyouhavereadconcerningelectrophilicaromaticsubstitutionreactions,suggestproductsforthefollowingreactions:a.

b.

c.

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10. Suggestsynthesesforthefollowingfrombenzeneandanyotherinorganicororganicreagents.a.

b.

c.

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d.

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e.

f.

Ammoniumpolysulfidewillreduceonenitrogroupwhentwonitrogroupsareattachedtoanaromaticring.

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g.

h.

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11. Giveanexplanationforthefollowingobservation:

Theorthoandparaproductspredominate,becausethemethylgroupassistsinthedelocalizationofthepositivelychargebenzenoniumintermediatethroughhyperconjugation.Metaattackwouldnotallowthemethylgrouptoparticipateinthedelocalizationofthepositivecharge.

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and

12. Givearationaleforthefollowingobservation:

Nitrationoft-butylbenzeneproduces16%oftheorthoproductand80%oftheparaproduct;however,nitrationofmethylbenzene,toluene,produces58%oftheorthoproductand38%oftheparaproduct.Thet-butylgroupstericallyinhibitsattackattheorthoposition;therefore,theparaproductwouldbefavored.Thisisnotthecaseforthesmallermethyl

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group;therefore,statistically,theorthoproductwouldbefavoredsincetherearetwositesavailablefortheformationoftheorthoproductandonesiteavailablefortheformationoftheparaproduct.

13. Indicateusinganarrowtheposition(s)mostlikelytoundergoelectrophilicaromaticsubstitutionineachofthefollowingcompounds:

(a)o-xylene(b)m-nitrotoluene(c)p-bromotoluene(d)m-methylphenol(e)o-bromotoluene(f)m-chloronitrobenzene(g)m-xylene(a)

b.

Thefollowingistheoreticallypossible,butthegroupswouldbecrowded;therefore,itwouldbeaminorproductduetostericcrowding:

c.

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d.

Thefollowingistheoreticallypossible,butthegroupswouldbecrowded;therefore,itwouldbeaminorproductduetostericcrowding:

e.

Thefollowingistheoreticallypossible,butthegroupswouldbecrowded;therefore,itwouldbeaminorproductduetostericcrowding:

(f)

Thefollowingistheoreticallypossible,butthegroupswouldbecrowded;therefore,itwouldbeaminorproductduetostericcrowding:

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(g)

Thefollowingistheoreticallypossible,butthegroupswouldbecrowded;therefore,itwouldbeaminorproductduetostericcrowding:

14. Drawstructuresfortheprinciplemononitrationproductsof:

(a)

(b)

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(c)

(d)

(e)

(f)

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15. Suggestamechanismforthefollowingreaction:

1.

2.

3.

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4.

16. OnemoleofcompoundA,C16H16,reactswithBr2/CCl4,diluteKMnO4,andonemoleofH2/Pt.TreatmentwithhotconcentratedKMnO4givesadicarboxylicacidwhichhasonlyonemonobromosubstitutionproduct.OzonolysisofcompoundAgivesacompoundthathastwomonobromosubstitutedproducts.WhatisthestructureofA.?Followingisonepossiblesolution.Canyouthinkofanother?1.Reactionwithbromineincarbontetrachloride:

2.Reactionwithdilutepotassiumpermanganate

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3. Reactionwithonemoleofhydrogen:

4. Reactionwithconcentratedhotpotassiumpermanganateinacidicsolution.

5. Ozonolysis

17. Supplystructuresforthefollowingpathway:C7H8+Br2/light→A+Mg+dryether→C7H7MgBrC7H7MgBr+D2O→C7H7DC7H7D+H2S2O7→C7H6DSO3HC7H6DSO3H+D2O→C7H6D2

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statisticallyanticipatedyields

18. Suggestasynthesisfor

CH2 C

O

from C C

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19.Giveanexplanationforthefactthatthesulfonationreactioninaromatic

substitutionreactionsisreversible.Theenergybarrierfromreactantstoproductisthesameastheenergybarrierforproductstoreactants: