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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:
