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Luminol and Chemiluminescence
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Name:MohitN.Mulani ExperimentDueDate:2/20/14
Sectioninstructor:BrianKasper Section:231
LuminolandChemiluminescence
1)In3nitrophthalicacid,thecarboxylicwhichismoreacidicisatthe2positionwithpKa=2.
Inthisconjugatedringsystem,thenitrogroupactsasapowerfulelectronwithdrawinggroup
(deactivatingagent)whichservestoremove/pullawayelectrondensityfromthecarboxylicacidgroups
andmakethemmoreelectrophilicwhichstabilizestheconjugatebase(anion)andmakesiteasierforit
tolosetheH+.Thiseffectofthenitrogroupisfeltmuchmorestronglybythecarboxylicgroupcloserto
itontheorthoposition(w.r.tit)thantheotheroneinthemetapositionmakingitmoreacidic.
2)TocalculatetheKeq,weneedthepKavaluesoftheacidandtheconjugateacid.Wehaveoneof
these(for3nitrophthalicacid:2)andtofindtheother,wecanusethepKbvalueofHydrazinewhichis
5.77.AsthesumofthepKbandpKavaluesforaconjugatepairis14,wecancalculateittobe8.23.
Makingdissociationequationsfortheacidsanddividingthemtogettheoriginalreaction,weseethat
pKeqis28.23=6.23.Keqthereforeis106.23or1.7x106.
3)Thereactionof3nitrophthalicacidandHydrazinecouldgobothwaysbutonlytheonewhich
involvesthereplacementoftheOHgroupwithaminegroup(NH)andthentheintramolecular
replacementoftheotherOHgroupof3nitrophthalicacidwiththeotheraminegroupisfavoured.This
reactionismorelikelytohappenbecauseasitisintramolecular,itisfasterthantheminoronewhich
involves2moleculesofhydrazineattackingtheseparateOHgroups.Wevealsoestablishedthat
becauseofitspositionrelativetothenitrogrouponeofthecarboxylicgroupsismoreacidicwhich
makesitmorelikelytobetheonewhichisattackedfirstfollowedbyanintramolecularreaction.
4)ThepKbvalueforethant1,3diamineishigherthanthatofhydrazine(itisaweakerbase)which
meansthesubsequentpKaoftheconjugateacidwillbesmallermakingitsKeqhigher.Thislowersthe
Keqoftheoriginalreaction(whichiscalculatedastheratioofacidKeqandconjugateacidKeqimplying
thattherateofforwardreactionhasbeenlowered.Theproductformedasaresultofreactingtheacid
withethane1,3diaminewillbeamuchlargerringastheamidegroupnowattacksthecarboxylicacid
forminganeightmemberedring.Eightmemberedringsascomparedtosixmemberedrings(nostrainin
chairconformation)orfivememberedrings(onlytorsionalstrain)havebothtorsionalstrainandsteric
strain.Thismakesitmoreunstable.
5)Thisoccursbecauseamidesarelessbasicthanaminesonaccountofresonancestabilization.The
resonanceoccursduetothepresenceofalonepaironNitrogenwhichisdelocalizedbetweenitandthe
electronegativeoxygenofthecarbonylgroup.
6)485nm.TheluminolontreatmentwithK3Fe(CN)6/H2O2emitslightwhichhasabrightblue(almost
cyan)colourwhichcorrespondstothehighendofthebluewavelength(450500nm),edgingtowards
greenratherthanviolet.Thislightwouldbeamixtureofseveralwavelengthsaroundthehigherendof
thisrangesoIselected485nm.
7)Itwouldbeaterriblelightsourcebecauseoftheshorttimeitsglowlasts(onlyafewseconds).This
wouldmeanconstantreactionsofluminolwithoxidisingagentswhichiscostlyanddifficultifthesignis
torun24hoursaday.
8)A)Luminol:Exactmass177.05g
Massoftwomostabundantisotopes:177.05g,178.06g.
Luciferin:Exactmass280.00g
Massoftwomostabundantisotopes:280.00g,281.00g.
B)Luminolwouldhaveauniquesignalataround3000cm1associatedwiththeNHgroupand
Luciferinwouldalsohavearecognizablesignalduetothepresenceofsulphursinglebondedtocarbon
initsheterocyclicsystem.
C)Luminolhas7signals(with2uniquecarbonsatthecentreofthebicyclicsystemhavingthesame
energywithashiftdifferenceofabout1ppm)andLuciferinhas11signalswithdifferentchemicalshifts.
D)Luminolhas5signalsandLuciferinhas8signals.