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SolutionstoProblemsCarboxylicAcids
BuildingBridgestoKnowledge
PhotoofaFreewayinShanghai,China
1. Arrangethefollowingacidinorderofincreasingacidity:propanoicacid;2-fluoropropanoicacid,3-fluoropropanoicacid,2,2-difluoropropanoicacid,3,3-difluoropropanoicacid.
2,2-difluoropropanoicacid>2-fluoropropanoicacid>3,3- difluoropropanoicacid>3-fluoropropanoicacid2. Whichcompound,propanoicacidor2-phenylpropanoicacid,wouldhavethe
higherpKavalue?Givearationaleforyourselection.
2-phenylpropanoicacidwouldhavealowerpKa,i.e.,2- phenylpropanoicacidisastrongeracid,becauseofthe inductiveeffect(electronwithdrawingeffect)ofthephenylgroup.3.Suggestasynthesisforbenzoicacidfrombenzeneastheonlysourceoforganic
startingmaterialandanyothernecessaryinorganicmaterials.
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4.Suggestasynthesisfor4-phenylbutanoicacidfrombenzeneandanyothernecessaryorganicandinorganicmaterials.
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5.Whichofthefollowingcompoundswouldhavethehighestboilingpoint?Givea
rationaleforyouranswer.
(a) CH3(CH2)4CH3(b) CH3(CH2)3CH2OH(c) CH3(CH2)2COOH(d) CH3(CH2)2CH2SH
(c)>(b)>(d)>(a)
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6. Ifastudenthad100.0mLofa0.050Msolutionofaceticacidand100.0mLofa0.100Msolutionofsodiumacetate,whatvolumeoftheweakacidsolutionwouldshehavetomixwiththeconjugatebasesolutioninordertoprepare75.0mLofabuffersolutionwithapHof5.0?ThepKaforaceticacidis4.7.
Letx=volumeinmLoftheCH3COO-Na+ Then,75.0-x=volumeinmLoftheCH3COOH
5.0 − 4.7 = log
millimole of CH3COO− Na+
75.0 mLmillimoles of CH3COOH
75.0 mL
⎛
⎝
⎜⎜⎜
⎞
⎠
⎟⎟⎟
0.3 = log 0.100 x mmoles3.75 mmoles - 0.050x mmoles
⎛⎝⎜
⎞⎠⎟
2.0 = 0.100 x mmoles3.75 mmoles - 0.050x mmoles
⎛⎝⎜
⎞⎠⎟
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x,i.e.,37.5mL,isthevolumeofthe0.100Mofsodiumacetateneeded,and75.0-xor37.5mLof0.050Maceticacidwouldgive75.0mLofabuffersolutionwithapHequalto5.0. 7.BenzaldehydereactedwithchromicacidtoformacompoundthatreactedwithpropylalcoholinaDean-Starkapparatustoformacompoundthathasantimicrobialproperties.Thecompoundalsohasanuttyodorandanut-liketaste.Suggestastructuralformulaforthissweetandfruitytastingcompound.
8. ListthefollowingacidsinorderincreasingpKavalues. (a)
(b)
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(c)
(d)
(a) >(b)>(c)>(d)
9.Suggestasynthesisforthefollowingfromthegivencompoundandanyothernecessaryinorganicandorganicmaterials.
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10. Suggestasynthesisforthefollowingfromtheindicatedstarting materialandanynecessaryinorganicreagents.
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11. Suggestasynthesisforthefollowingfromtheindicatedstarting materialandanyothernecessaryinorganicororganicmaterials.
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12.Suggestasynthesisforthefollowingfromtheindicatedstarting materialandanyothernecessaryinorganicororganicmaterials.
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13.2,5-Diethyl-1,1-cyclopentanedicarboxylicacidwasisolatedasopticallyinactivecompoundA(aracemicmixture)andopticallyinactivecompoundB.AandBhavedifferentmeltingpoints.
CompoundAyieldstwo2,5-diethylcyclopentanecarboxylicacidswhenitisheated.CompoundByieldsone2,5-diethylcyclopentanecarboxylicacidswhenitisheated.(a) SuggeststructuresforAandB
(2R,5R)(2S,5S)opticallyactiveopticallyactive CompoundA
CompoundB (2R,5S)
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CompoundBisthe(2R,5S)compound,amesocompound,thatisidenticaltothe(2S,5R)isomer;therefore,themoleculeisopticallyinactive.
(b) Suggeststructure(s)fortheproduct(s)formedfromheatingcompoundA.
Decarboxylationofthe(2R,5R)isomerwouldproduceasingle compound,the(2R,5R)decarboxylatedcompound.
Decarboxylationofthe(2S,5S)isomerwouldproduceasingle compound,the(2S,5S)decarboxylatedcompound.
Consequently,decarboxylationofthetwoisomersthatcomprisecompoundAproducestwodecarboxylatedisomers,andeachisomerisopticallyactive.(c) Suggeststructure(s)fortheproduct(s)formedfromheatingcompoundB.
Decarboxylationofthe(2R,5S)isomerwouldproduceasinglecompound,the(2R,5S)decarboxylatedcompound.Thedecarboxylationproductisopticallyinactive;furthermore,removingeithercarboxylicacidgroupwouldproducethesamecompound.
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(d) Writemechanismstoaccountfortheseobservations.
Theseriesofelementarystepsfordecarboxylatingthepreviouslymentionedgem-dicarboxylicacidswouldbe:(1)
(2)