254048312 5 Key Factors That Affect Acidity in Organic Chemistry Master Organic Chemistry PDF

Preview

Summary

Key Factors That Affect Acidity in Organic Chemistry Master Organic Chemistry...

Description

12/17/2014

5KeyFactorsThatAffectAcidityinOrganicChemistry—MasterOrganicChemistry

Home Blog Mission OnlineTutoring ReactionGuide Feedback MembersLogin MasterOrganicChemistry Enteranorganicchemistrys

New?StartHere Organic1Index Organic2Index StudyAndExamTips SummarySheets Feedback

FiveKeyFactorsThatInfluenceAcidity byJames inAlcohols,Alkanes,Alkenes,Alkynes,Carboxylicacids,ChemicalBonds,Esters,FunctionalGroups, Ketones,OrganicChemistry1,UnderstandingElectronFlow,WhereElectronsAre I’vewritteninschoolmarmishtonesbeforeabouthowpKaisoneofthemostimportantmeasuresyou canlearninorganicchemistry,andnotknowingsomebasicpKavaluesbeforeanexamisalotlike walkinguptoapokertablewithoutknowingthevaluesofthehands:you’regoingtoloseyourshirt. Todaywe’lltalkaboutwhat’sbehindthetrendsinacidityfordifferentmoleculesanddiscussthemost importantfactorsthatdeterminethesevalues.Beforewegetstarted,however,let’squicklyreviewthe basicsofacidityandbasicity.Here’sthecondensedversion: 1. Bronstedacidsareprotondonors,Lewisacidsareelectronpairacceptors.Converse:Bronsted base=protonacceptor,Lewisbase=electronpairdonor. 2. Aconjugatebaseiswhatyouobtainwhenyouremoveaproton(H+)fromacompound.For instance,HO()istheconjugatebaseofwater.O(2)istheconjugatebaseofHO().Conversely, conjugateacidsarewhatyouobtainwhenyouaddaprotontoacompound.Theconjugateacidof waterisH3O(+). 3. Quickquiz:ispH1acidicorbasic?pKaissimilartopHinthatlow(andevennegativevalues) denotestrongacids.That’sbecausepKaisbasedontheequilibrium: http://www.masterorganicchemistry.com/2010/09/22/fivekeyfactorsthatinfluenceacidity/

1/23

12/17/2014

5KeyFactorsThatAffectAcidityinOrganicChemistry—MasterOrganicChemistry

4. Accordingtothis,anythingwhichstabilizestheconjugatebasewillincreasetheacidity. ThereforepKaisalsoameasureofhowstabletheconjugatebaseis.Putanotherway,strongacids haveweakconjugatebases,andviceversa. Withthatoutoftheway,let’sgetstarted. Factor#1–Charge. Removalofaproton,H+,decreasestheformalchargeonanatomormoleculebyoneunit.Thisis,of course,easiesttodowhenanatombearsachargeof+1inthefirstplace,andbecomesprogressively moredifficultastheoverallchargebecomesnegative.Theaciditytrendsreflectthis:

Notethatonceaconjugatebase(B)isnegative,aseconddeprotonationwillmakethedianion(B2). Whilefarfromimpossible,formingthedianioncanbedifficultduetothebuildupofnegativechargeand thecorrespondingelectronicrepulsionsthatresult. Factor#2–TheRoleoftheAtom Thispointcausesalotofconfusionduetothepresenceoftwoseeminglyconflictingtrends. Here’sthefirstpoint:acidityincreasesaswegoacrossarowintheperiodictable.Thismakessense, right?ItmakessensethatHFismoreelectronegativethanH2O,NH3,andCH4duetothegreater electronegativityoffluorineversusoxygen,nitrogen,andcarbon.Afluorinebearinganegativechargeis ahappyfluorine. Buthere’stheseeminglystrangething.HFitselfisnota“strong”acid,atleastnotinthesensethatit ionizescompletelyinwater.HFisaweakeracidthanHCl,HBr,andHI.What’sgoingonhere?

http://www.masterorganicchemistry.com/2010/09/22/fivekeyfactorsthatinfluenceacidity/

2/23

12/17/2014

5KeyFactorsThatAffectAcidityinOrganicChemistry—MasterOrganicChemistry

Youcouldmaketwoargumentsforwhythisis.Thefirstreasonhastodowiththeshorter(andstronger) HFbondascomparedtothelargerhydrogenhalides.Thesecondhastodowiththestabilityofthe conjugatebase.Thefluorideanion,F(–)isatinyandviciouslittlebeast,withthesmallestionicradiusof anyotherionbearingasinglenegativecharge.Itschargeisthereforespreadoverasmallervolumethan thoseofthelargerhalides,whichisenergeticallyunfavorable:foronething,F(–)begsforsolvation, whichwillleadtoalowerentropytermintheΔG. NotethatthistrendalsoholdsforH2OandH2S,withH2Sbeingabout10milliontimesmoreacidic. Factor#3–Resonance. Ahugestabilizingfactorforaconjugatebaseisifthenegativechargecanbedelocalizedthrough resonance.Theclassicexamplesarewithphenol(C6H5OH)whichisaboutamilliontimesmoreacidic thanwater,andwithaceticacid(pKaof~5).

http://www.masterorganicchemistry.com/2010/09/22/fivekeyfactorsthatinfluenceacidity/

3/23

12/17/2014

5KeyFactorsThatAffectAcidityinOrganicChemistry—MasterOrganicChemistry

Watchoutthough–itisn’tenoughforaπsystemtosimplybeadjacenttoaproton–theelectronsofthe conjugatebasehavetobeinanorbitalwhichallowsforeffectiveoverlap(foradastardlytrickquestion inthisveinthatroutinelystymiesHarvardpremeds,lookhere.) Factor#4–Inductiveeffects.Electronegativeatomscandrawnegativechargetowardthemselves, whichcanleadtoconsiderablestabilizationofconjugatebases.Checkouttheseexamples:

Predictably,thiseffectisgoingtoberelatedtotwomajorfactors:1)theelectronegativityoftheelement http://www.masterorganicchemistry.com/2010/09/22/fivekeyfactorsthatinfluenceacidity/

4/23

12/17/2014

5KeyFactorsThatAffectAcidityinOrganicChemistry—MasterOrganicChemistry

(themoreelectronegative,themoreacidic)andthedistancebetweentheelectronegativeelementandthe negativecharge. Factor#5–Orbitals.Again,theacidityrelatesnicelytothestabilityoftheconjugatebase.Andthe stabilityoftheconjugatebasedependsonhowwellitcanaccomodateitsnewfoundpairofelectrons.In aneffectakintoelectronegativity,themorescharacterintheorbital,theclosertheelectronswillbeto thenucleus,andthelowerinenergy(=stable!)theywillbe.

LookatthedifferencebetweenthepKaofacetyleneandalkanes–25!That’s10tothepowerof25,as in,“100timesbiggerthanAvogadro’snumber”.Justtogiveyouanideaofscale.That’stheamazing thingaboutchemistry–thesheerrangeinthepowerofdifferentphenomenaisaweinspiring. There’sactuallyamnemonicI’vefoundthatcanhelpyouremembertheseeffects.ThisiscreditedtoDr. ChristinePruis,SeniorLectureratArizonaStateUniversityTempe. Charge Atom Resonance DipoleInduction Orbitals =CARDIO. Treadcarefullywithmnemonics,butthereyougo.

http://www.masterorganicchemistry.com/2010/09/22/fivekeyfactorsthatinfluenceacidity/

5/23

12/17/2014

5KeyFactorsThatAffectAcidityinOrganicChemistry—MasterOrganicChemistry

11

0

5 Tweet

159 Share

RelatedPosts: HowtoUseapKaTable Alcohols(3)–AcidityandBasicity WalkthroughofAcidBaseReactions(3)–AcidityTrends WalkthroughofAcidBaseReactions(2):Basicity Taggedas:acidity,acids,bases,basicity,chargestability,conjugateacid,conjugatebase,dipoles, electronegativity,hybridization,polarizability,resonance {45comments…readthembeloworaddone}

HeeroFongJanuary12,2011at12:54pm Ijustwantedtosayyouaredoinganabsolutelyfantasticjobofteachingorganicchemistryand makingitcomprehensible.I’vebeenreadingyourpostsforthelastfewdays,andmaterialwhich wasalientomebeforeasfinallystartedtomakesense. Thanks! Reply

JamesJanuary12,2011at7:09pm Thanks! Reply

howaidajouniMarch12,2011at4:19pm thanksformakingorgchemistryeasierbutihaveaquestionaboutresonance,youdidntmention http://www.masterorganicchemistry.com/2010/09/22/fivekeyfactorsthatinfluenceacidity/

6/23

12/17/2014

5KeyFactorsThatAffectAcidityinOrganicChemistry—MasterOrganicChemistry

electrondonationorwithdrawalbyresonance Reply

JamesMarch13,2011at1:32pm That’sathornyissue…itcanbehardtoseparatetheinfluenceofinductiveandresonance effects.Doyouhaveaspecificexamplethatyou’rethinkingof? Reply

AliOctober19,2011at2:36am Iwasthemostconfusedpersonwhocouldnotunderstandtheconcept.Ireadyournote.Ireceived 100%onAciditypartonmyExam.Thankyou! Reply

jamesOctober19,2011at3:10am Thisisthekindofcommentthatmakesmyday.Thanks! Reply

PatNovember5,2011at12:03am Ilovethissite…Ihatereadingorganicchemtxtbooksbecausemostareboooooringbutyoumake studyingforOchemthehighlightofmyfridayevening…Youarefunny,andyourdeliverystyle isabsolutelyamazing!!IaminOchemII,barelymadeitthroughthefirstbutIamexcellinginmy second….Thankyousirfordoingthis!!Iappreciateitmorethanyouknow…Goodday! Reply

LaraFebruary14,2012at1:24am Thankyousomuchforthissummarysheet,Iwashavingsomuchtroubletryingtofigureoutwhat madeamoleculemoreacidic–andhereitallis!Fullyexplainedandeasilyunderstandable. Fantasticstuff. Reply

LainaMarch12,2012at7:06pm http://www.masterorganicchemistry.com/2010/09/22/fivekeyfactorsthatinfluenceacidity/

7/23

12/17/2014

5KeyFactorsThatAffectAcidityinOrganicChemistry—MasterOrganicChemistry

Ijustwantedtothankyouforalltheworkyouputintothissite.I’manundergraduateatYaleand forthepastsemester,I’vebeenafraidI’llfailOrgo.Thankstoyoursite,Inolongerfeelasstressed becauseyou’vedonesuchagoodjobofexplainingthings.So,yes,thankyou!! Wishingyouthebest! Reply

jamesMarch13,2012at8:56am ThanksLaina.Gladyoufindituseful.LetmeknowiftheresanythingIcandotomakethe sitemorehelpfulforyourneeds. Reply

AlaMarch22,2012at6:03pm IhaveaproblemwhereIhavetodeterminethemoststableconjugatebase,whichindicatesthe strongestacid.Ijustwanttoknow,isitpossibletohaveastrongacidaccordingtoitspKavalue, butaccordingtoatom,resonance,etc.anotheracidisstronger? Reply

jamesMarch23,2012at5:31pm pKarepresentsanexperimentalmeasurement.Experimentalmeasurementsareprimary–the conceptswepulloutofthem,suchasthefactorsmentioned,aresecondary.Sowhatyou’re mentioningisn’tpossible,assumingallothervariablesarethesame. Reply

MarianaApril24,2012at7:27pm Ijustdon’tseemtounderstandwhydoesionicradiusincreaseacidity?Imean,BindingEnergy decreasesandit’smoreeasytoloseanelectron,ifacidsarecompoundsthatacceptelectronshow doesacidityincrease? Reply

jamesApril26,2012at8:16pm Basicityisallaboutthestabilityofnegativecharge.Withlargeratoms,essentiallythe chargeismorespreadoutoveragreatervolume.Lowerchargedensitiesaremorestable. Seealsohere:http://masterorganicchemistry.com/2012/04/25/walkthroughofacidbase http://www.masterorganicchemistry.com/2010/09/22/fivekeyfactorsthatinfluenceacidity/

8/23

12/17/2014

5KeyFactorsThatAffectAcidityinOrganicChemistry—MasterOrganicChemistry

reactions3aciditytrends/ Reply

NaomiBowensJune2,2012at3:44am Ifeelsooomuchmoreconfidentaboutorgobcofu=) Reply

GuvanthiJuly29,2012at5:03pm Allthesestuffwereveryusefultome.GottoknowmorethingsthatIdidn’tknowbefore.Thanks alot..!Similararticleonbasicitywillbeappreciatedalot..! Reply

TomAugust1,2012at7:22pm OnthefiguredescribinginductiveeffectsonpKaofcarboxylicacidsyouhavebromoaceticacid withpKaof2.86ononelineand2.97onthenext.Whythedifference? Reply

jamesAugust6,2012at9:57pm Fixed.Thanksforthespot–Evans’pKatablesays2.86.NotsurewhereIpulledthe2.97 from. Reply

LuisSanchezSeptember7,2012at12:05am Thissiteissohelpful.Itmakesorganicchemistrywayeasier.Thankyou! Reply

jamesSeptember8,2012at7:11pm GladyoufindithelpfulLuis. Reply http://www.masterorganicchemistry.com/2010/09/22/fivekeyfactorsthatinfluenceacidity/

9/23

12/17/2014

5KeyFactorsThatAffectAcidityinOrganicChemistry—MasterOrganicChemistry

streaSeptember12,2012at5:34pm Ohwow,thisisamazing.Iwasstartingtothinktherewasnosite/bookthathadexactlythis information,thiscompactly(andbrilliantly,mightIadd)presented.Thankyousomuch!You’ve gotnoideahowmuchthishelped(andhowmuchitreducedmystudytime,godknowswecanall dowithextratimeonourhands:)).Thanksagain! Reply

YashFebruary20,2013at10:25pm Thisisawesome:D!Ineverquitegotaholdofthistopicsincethepast23monthsandnowafter readingthispageit’sallcrystalcleartome!Andasforthemnemonic,whenitoldittomychem teacher,hewasimpressedandaskedmeforthewebsite:D!Greatjob,keepitup:D Reply

jamesFebruary22,2013at3:59pm Great,gladyoufoundituseful! Reply

AnnieMarch1,2013at7:41pm CanyoupleasemakethesenotesavailableasPDF? Thanks. Reply

AkashSharmaApril16,2013at2:38am youcanuseweb2pdfforthat…… googleit… italsohasbrowserplugin.. Reply

AkashSharmaApril16,2013at2:34am Organicismyfavouritepartinchemistry.Yourpostandcontentsprovidedmeagoodquick http://www.masterorganicchemistry.com/2010/09/22/fivekeyfactorsthatinfluenceacidity/

10/23

12/17/2014

5KeyFactorsThatAffectAcidityinOrganicChemistry—MasterOrganicChemistry

revisionbeforemyexamsandIdidextremelywell….. Thankstoyou….youhaveagoodwayofteachingorganicchemistry.. Iwoulddefinitelyrecommendthissitetomyfriendswhothinkorganicisboaringsubject…. Onceagainthanks….. Reply

ChrisJune12,2013at10:42am IamcurioushowyoucameupwiththisCARDIOacronym?Andwhen?Ihavehearditfromone otherpersonafewyearsago. Reply

jamesJune19,2013at9:04pm IshamelesslystoleitfromacommentthreadonSDN. Reply

PegahBiparvaJune12,2013at6:53pm DidyougettheCARDIOacronymfromaDr.ChristinePruisorChad’sReviewsfromArizona StateUniversity?Dr.PruisisourOrganicChemistryprofessorandcameupwiththisacronym78 yearsago,soperhapsthatisthe‘credit’youspeakof?Ifso,thatisawesome! Reply

EmilySeptember23,2013at3:26pm ThiswasreallyclearandhelpfulThankyousomuch!! Reply

JamesAshenhurstSeptember24,2013at10:30pm Awesome,gladtohearit. Reply

vickyOctober28,2013at10:18am

http://www.masterorganicchemistry.com/2010/09/22/fivekeyfactorsthatinfluenceacidity/

11/23

12/17/2014

5KeyFactorsThatAffectAcidityinOrganicChemistry—MasterOrganicChemistry

ididntget5pointorbitalasscharacterincreasesthentshouldbesp3< sp2H+AasyoumakeAmorestable? Reply

HannahNovember7,2014at2:23pm thiswassohelpfulthankyou! Reply LeaveaComment Name* Email* Website

Submit

SignUpToGetWeekly OrganicChemistryTips Andgetthefree"HowToSucceedInOrganicChemistry"Ebook Pleaseenteryourfirstname* Pleaseenteryouremail*

Signmeup!

AboutMasterOrganicChemistry Imaginehavingacomprehensiveonlineguidetohelpyousolveyourown problemsinorganicchemistry.That'smymissionwiththissite.Afterearninga Ph.D.atMcGillanddoingapostdocatMIT,Iappliedtobeaprofessor.That didn'tworkout.SoIdecidedtoteachorganicchemistryanyway.MasterOrganic ChemistryisthesiteIwishIhadwhenIwaslearningthesubject.

http://www.masterorganicchemistry.com/2010/09/22/fivekeyfactorsthatinfluenceacidity/

14/23

12/17/2014

5KeyFactorsThatAffectAcidityinOrganicChemistry—MasterOrganicChemistry

OrganicChemistryGuides

ReactionGuideMemberLogin Youarenotcurrentlyloggedin. Username: Password: RememberMe Login

»Register »LostyourPassword?

FollowonFeedly

GetTheLatestUpdates facebook twitter rss email RecentPosts PopularPosts RecentComments CleavageOfEthersWithAcidPostedon:Nov19,2014

EtherSynthesisViaAlcoholsAndAcidPostedon:Nov14,2014

http://www.masterorganicchemistry.com/2010/09/22/fivekeyfactorsthatinfluenceacidity/

15/23

12/17/2014

5KeyFactorsThatAffectAcidityinOrganicChemistry—MasterOrganicChemistry

SynthesisofEthers(2)BackToTheFuturePostedon:Nov07,2014 MasterOrganicChemistryThe(Short)VideoPostedon:Oct31,2014 WilliamsonEtherSynthesis:PlanningPostedon:Oct30,2014 Copyright©2014MasterOrganicChemistry.com.Allrightsreserved OrganicChemistryIsAwesome AboutJames Account AdvancedSubstitutionTopics–SunNov10 AlkeneCrashCourse–Thanks! AlkeneMiniCourse–Thanks! AlkeneMiniCourse AlkeneWebinar Alkenes:CommonExamProblems(WithSolutions) AlkyneWebinarSunDec15at9pmEST AlkynesAreABlankCanvas Blog CommonMistakesInOrganicChemistry:PentavalentCarbon Confirmingyouremailaddress… CrashCourseOnAlkenes CrashCourseOnAlkenes–Checkout Dashboard Don’tBeFutyl,LearnTheButyls EliminationWebinar–SundayNov24at9pmEST Feedback FormStylingSandboxPage FromGenChemToOrganicChem GettingStarted Home HowToDrawACyclohexaneChair HowToSucceedInOrganicChemistry HowToSucceedInOrganicChemistry Initiation,Propagation,Termination Interview IntroductionToSpectroscopySeminar IntroductionToSubstitutionWebinarTuesdayNov5 LeahNomenclatureGuestPost MembersLogin Mission NewAcidBaseWebinar NEW!ReagentsApp NMRVideoCheckout October22AcidBaseWebinar OnlineOrganicChemistryTutoring OnlineOrganicChemistryTutoring http://www.masterorganicchemistry.com/2010/09/22/fivekeyfactorsthatinfluenceacidity/

16/23

12/17/2014

5KeyFactorsThatAffectAcidityinOrganicChemistry—MasterOrganicChemistry

Org2PostIndex Organic1 Organic2 OrganicChemistryStudyAdvice PostIndex PostIndex2 PostIndexDraft postindexdraft2 Premium Products OrganicChemistryReagentGuide ReactionGuide 1,4additionofenolatestoenones(“TheMichaelReaction”) 1,4additionofnucleophilestoenones 1,4additionoforganocuprates(Gilmanreagents)toenones Acidiccleavageofethers(SN2) AdditionOfAlcoholsToAlkenesWithAcid Additionofaqueousacidtoalkenestogivealcohols AdditionofDichlorocarbenetoalkenestogivedichlorocyclopropanes Additionofdichloromethylenecarbenetoalkenes AdditionofGrignardreagentstoaldehydestogivesecondaryalcohols AdditionofGrignardreagentstoesterstogivetertiaryalcohols AdditionofGrignardreagentstoformaldehydetogiveprimaryalcohols AdditionofGrignardreagentstoketonestogivetertiaryalcohols AdditionofGrignardreagentstonitrilestogiveketones(afterhydrolysis) AdditionofHBroncetoalkynestogivealkenylbromides AdditionofHBrtoAlkenes AdditionofHBrtwicetoalkynestogivegeminaldibromides AdditionofHCloncetoalkynestogivealkenylchlorides AdditionofHCltoAlkenestoGiveAlkyl...