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SolutionstoProblemsCarboxylicAcids

BuildingBridgestoKnowledge

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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)