AnAnalysisofMassSpectralIsotopePatternsofCompounds化合物的质谱同位素模式分析

1MyReasonsforthisPresentationPresentresultsobtainedatPGCCShowthatcontentfoundintextbookscanbeimprovedMotivatestudents2IsotopesofBrandClaLow

massbHighmassRatio(a/b)RoundedratioVariable#atomsBr79

(50.69)81(49.31)1.0281:1mCl35(75.78)37(24.22)3.1293:1n3MassSpectrometer4Schematicdiagramofamassspectrometer567WhyBrandCl?Molecular-ionpeaksofC10H20Br1Cl1,C10H19Br2Cl1andC10H18Br3Cl1.8Premise

Inlieuofpatternmatching,

itshouldbepossibletodeterminethenumberofBrandClatomsinamolecularformulaofacompoundbyanalyzingthemolecular-ioncluster(i.e.,byclusteranalysis).9HerbertC.Brown

NobelLaureateHydroboration-oxidationwithBH3(CHM201)ReductionwithNaBH4(CHM202/204)10LillianBerg

NVCC-Annandale111213141516171819ChlorineConstant20BromineConstant

IM=3n212223TheoreticalConsiderations

IdealCompounds

Br(a:b)=1:1Cl(a:b)=3:1

13Cand2Hnegligible24BromineBinomialRatio(a:b)=1:1(1a+1b)mforBrm(1a+1b)1=1a+1b=1:1(1a+1b)2=1a2+2ab

+1b2=1:2:125ChlorineBinomialRatio(a:b)=3:1(3a+1b)nforCln(3a+1b)1=3a+1b=3:1(3a+b)2=9a2+6ab+1b2=9:6:126IdealModel=BinomialPair(1a+1b)m(3a+1b)nBr1Cl13a2+4ab+1b2=3:4:127Results(1a+1b)m(3a+1b)n=1m3na(m

+n)+….+1m1nb(m

+n)I(L/R)=1m3n/1m1nIM=3n

ChlorineRule:

WhenIequals1,3,9,27or81;nis0,1,2,3,or4,respectively,wheren=numberofchlorineatoms.

ThenumberofbromineatomsmequalsA–n.J.Chem.Educ.2004,81,1161-1168(articleavailableatfrontdesk)28RoaldHoffmann-NobelLaureateConservationoforbitalsymmetry“Oxygen”PriestleyvsSheeleHoffmannDjerassi

Woodward29GrossgivinglecturewithHoffmann,DjerassiandWoodwardlookingon.30StructureBegetsPropertiesLet’sexaminestructures.Assume3:1and1:1isotopicabundancesofchlorineandbromine.ConsiderBrm,ClnandBrmCln

compounds.31323334Results

N=2m4nN=2m2n2nN=2A2nChem.Educ.2003,8,182-18635SummaryPartI

forBrmCln

CompoundsDerivedachlorine-ruleequation,IM=3nAppliedittofindgrossstructuresofunknownsDerivedaunit-sampleequation,N=2A2n36Follow-ontotheChlorineRuleAnautomatedA+2isotope-patternanalyzer(IPA)IPAisonmywebsiteJ.Chem.Educ.,inpress37ExampleofaPrintOutofaMassSpectrumintheMolecular-IonRegionMassPercent22464.42254.3226100.02276.922845.62293.22306.438Molecular-IonDataisEnteredintotheIPA

TheExcelprogramreturnstheA+2(Cl,Br,S)compositionofthemolecularformula39HomeworkAssignment

for

SelectedStudentsPickupslipfromfrontdeskEnterdatafromyourslipintoIPAObtaintheCl,Br,Scomposition(e.g.,Br1Cl2)andrecorditonyourslipWriteyournameontheslipandturnitinnextTuesday.