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Solutions to the problems on pages 138 to 158 of "Spectroscopy, Building Bridges to Knowledge."
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1
SolutionstoSpectroscopyProblemsBuildingBridgestoKnowledge
PhotoexitingatunnelontheFreewayinShanghai,China
1. Convert3.96μmtocm-1
2. Giveabriefexplanationaboutthetheoryofinfraredspectroscopy.
Aninfraredspectrumoccurswhenthefrequencyofinfraredradiationincidentonorganicmoleculesequalsthefrequencyofthevibratingbondsattachedtoatomsinthemolecule.Theinfraredenergyabsorbedisequaltotheenergyassociatedwiththevibratingmolecule.Theradiationabsorbed
3.96 x 10−6 x 1 m1 x 106 m
x 100 cm1 m
= 3.96 x 10−4 cm = λ
ν cm−1 = 1λ
= 13.96 x 10−4 cm
= 2.53 x 103 cm−1
2
canbemeasured,orthelighttransmittedcanbemeasured.Thelightabsorbedortransmittedisrelatedtothewavelengthorwavenumbercorrespondingtothelightabsorbedortransmitted.
3. Calculatetheapproximatestretchingvibration,inwavenumbers,fortheC-Fbondiftheforceconstant,k,isapproximately760N/m.
4. Howmanyfundamentalvibrationsarepredictedforthenon-linearwatermolecule?Howmanyfundamentalvibrationsarepredictedforthelinearcarbondioxidemolecule?Thetheoreticalnumberoffundamentalvibrationsforwaterwouldbedeterminedby3n–6
3(3)-6=3
1λm
= νm−1 = 5.309 x 10−10 s
m760 kg-m/ms2
(12.0 g/6.022 x1023) x (19.0 g/6.022 x 1023)12.0 g
6.022 x 1023 + 19.0 g6.022 x 1023
1λm
= νm−1 = 5.309 x 10−10 s
m760 kg-m/ms2
(1.99 x 10−23 g) x (3.155 x 10−23 g)1.99 x 10−23 g + 3.155 x 10−23 g
1λm
= νm−1 = 5.309 x 10−10 s
m760 kg/s2
6.278 x 10−46 g2
5.145 x 10−23 g
1λm
= νm−1 = 5.309 x 10−10 s
m760 kg/s2
1.22 x 10−23 g
1λm
= νm−1 = 5.309 x 10−10 s
m760 kg/s2
1.22 x 10−23 g x 1 kg1000 g
1λm
= νm−1 = 5.309 x 10−10 m−1 x 2.50 x 1014 1
s = 1.33 x 105 m−1
1λcm
= νcm−1 = 1.33 x 105 m−1 x 1 m
100 cm = 1.33 x 103 cm−1
3
Thetheoreticalnumberoffundamentalvibrationsforthelinear moleculecarbondioxide,CO2,wouldbedeterminedby3n-5 3(3)-5=4
5. Listsfourreasonswhyallpredictedfundamentalvibrationsofabondmaynotappearintheinfraredspectrum.Thereisnochangeinthedipolemomentofthemoleculeduringvibration.Absorptionoccursoutsidetheregionofthespectrumunderobservation.
Thevibrationsresultinabsorptionssoclosethattheycoalesce. Theabsorptionsaretooweaktobeseen.
6. DrawtheexpectedfundamentalvibrationsforCO2andlabelthedegeneratemodes.Thenumberofvibrationsexpectedforcarbondioxide,alinearmolecule,wouldbe3(3)-5=4.Thefourpossiblevibrationmodesare:
4
Thetwobendingmodes,CandD,aredegenerate(thesameinenergy);therefore,onlyonebendingvibrationisobservedintheinfrared(IR).ThesymmetricalstretchingvibrationAdoesnotinvolveachangeindipolemoment,i.e.,thedipolemomentofAiszero;therefore,thisstretchingvibrationisinfraredinactive.Theseillustrationscanberepeatedforanyoftheaxes,andtheresultswouldbethesame.Sonomatterhowthemoleculemovesinspace,thereareonlytwovibrationsthatwouldbeIRactive–theasymmetricalstretchingvibrationandthebendingvibration.Therefore,theIRspectrumofcarbondioxidewouldbe:
7. UsingthedatainTable10.2,calculatethewavenumbersfortheC≡Nand
C≡Cstretchingvibrations.Thecalculatedwavenumberforthecarbon-nitrogentriplebondis:
1λm
= νm−1 = 5.309 x 10−10 s
m1750 kg-m/ms2
(12.0 g/6.022 x 1023)(14.0 g/6.022 x 1023)12.0 g
6.022 x 1023 + 14.0 g 6.022 x 1023
1λm
= νm−1 = 5.309 x 10−10 s
m1750 kg-m/ms2
1.07 x 10−23 g1λm
= νm−1 = 5.309 x 10−10 s
m1750 kg-m/ms2
1.07 x 10−23 g x 1 kg1000 g
1λm
= νm−1 = 5.309 x 10−10 s
m x 4.045 x 1014 1
s = 2.15 x 105 m−1
5
Thecalculatedwavenumberforthecarbon-carbontriplebondis:
8. PredictwhichofthefollowingcompoundswouldgivelittleornoC≡Cstretchingtransmittancebands:
(a)H-C≡C-CH3(b)H-C≡C-CH2CH3 (c)CH3C≡CCH3(d)CH3CH2CH2C≡CCH3
Theinfraredstretchingvibrationforthetriplebondin“c”wouldnotbeobservedbecausethereisnochangeinthedipolemomentofthemoleculeduringvibration.
9. Thecarbon-oxygendoublebondappearsatahigherwavenumber(higherfrequencyofinfraredradiation)thanthecarbon-oxygensinglebond.Giveanexplanationforthisobservation.Thecarbon-oxygendoublebondhasastrongerforceconstantthanthecarbon-oxygensinglebond,andtheforceconstantisdirectlyproportionaltothewavenumber.
10. Acertaincompoundgivesacarbonylabsorptionatapproximately1775cm-1.Whichofthefollowingcompoundswouldgiverisetoatransmittancebandat1775cm-1?Giveanexplanationforyourselection.
1λcm
= νcm−1 = 2.15 x 105 m−1 x 1 m
100 cm = 2.15 x 103 cm−1
1λm
= νm−1 = 5.309 x 10−10 s
m1560 kg-m/ms2
(12.0 g/6.022 x 1023)(12.0 g/6.022 x 1023)12.0 g
6.022 x 1023 + 12.0 g 6.022 x 1023
1λm
= νm−1 = 5.309 x 10−10 s
m1560 kg-m/ms2
9.95 x 10−24 g
1λm
= νm−1 = 5.309 x 10−10 s
m1560 kg-m/ms2
9.95 x 10−24 g x 1 kg1000 g
1λm
= νm−1 = 5.309 x 10−10 s
m x 3.96 x 1014 1
s = 2.10 x 105 m−1
1λcm
= νcm−1 = 2.10 x 105 m−1 x 1 m
100 cm = 2.10 x 103 cm−1
6
Theinfraredspectrumof“d”(cyclobutanone)wouldexhibitacarbonylabsorptionat1775cm-1.Cyclobutanonehasanglestrainsofabout19.5o,andthisstrainincreasesthenumericalvalueoftheforceconstant,k.Theforceconstantisdirectlyproportionaltothewavenumber;consequently,thewavenumberincreasesfromanexpectedvalueofabout1724cm-1to1775cm-1.
11.WhenacarbonylgroupisconjugatedwithaC-Cdoublebond,theconjugationlowerstheobservedwavenumberbyapproximately20cm-1ascomparedtoanonconjugatedcarbonyl.Forexample,compoundsAhasastrongtransmittancebandat1715cm-1andcompoundBhasastrongtransmittancebandat1685cm-1.
Basedonthetransmittancebandforcyclohexanoneat1715cm-1and1724cm-1forcyclopentanone,predicttheabsorptionfor
Thetransmittancebandfor2-cyclohexenonewouldbe1695cm-1,andthetransmittancebandfor2-cyclopentenonewouldbe1704cm-1.
CH3 C
O
CH3
O O O
a b c d
CH3
CH3
C H CH2 C CH3
O
C
CH3
CH3
CH C
O
CH3
A B
O O
and
7
12.Howcouldyouuseinfraredspectroscopytodistinguishbetweenthefollowingcompoundpairs?Indicatethecharacteristicabsorptionsexpectedforeachstructure.
(a)
Thecarboxylicacidwouldexhibitabroad0Hstretchingvibrationbetween3500cm-1-2500cm-1andacarbonylstretchingvibrationbetween1720cm-1-1696cm-1.ThealdehydewouldexhibitaC-Hstretchingvibrationofthehydrogenattachedtothecarbonylgroupbetween2830cm-1-2695cm-1,andacarbonylstretchingvibrationatabout1724cm-1.
(b)
Theketonewouldexhibitastretchingvibrationbetweenatapproximately1724cm-1.Theesterwouldexhibitacarbonylstretchingvibrationbetween1750cm-1-1735cm-1,andcarbon-oxygentransmittancebandsat1250cm-1and1051cm-1.(c)
2-Cyclohexenonewouldexhibitacarbonylstretchingvibrationat1695cm-1,andcyclohexanonewouldexhibitacarbonylstretchingvibrationat1715cm-1.
C
O
C
O
CH3CH2CH2 OH CH3CH2CH2 H
CH3C
O
C
O
CH3CH2CH2 CH3CH2CH2 OCH3
O O
8
(d)
Thenitrilewouldexhibitasharptransmittancebandbetween2260cm-1-2222cm-1.TheAlkynewouldnotexhibitatransmittancebandbetween2260cm-1-2100cm-1,becausethemoleculeissymmetrical;therefore,thereisnochangeinthedipolemomentofthemoleculeduringvibration.(e)
Cyclobutanone(transmittancebandatapproximately1780cm-1)ismorestrainedthancyclohexanone(transmittancebandatapproximately1715cm-1);therefore,thecarbonyltransmittanceband(approximately1780cm-1)forcyclobutanonewouldappearatahigherwavenumber.(f)
Thet-butylgroupischaracterizedbytwobendingvibrationsat1395cm-1–1385cm-1andamoreintensetransmittancebandnear1370cm-1.Thesetransmittancebandsarenotexhibited1-butanol.(g)
Theisopropylgroupischaracterizedbyastrongdoubletbetween1388cm-1–1380cm-1asaconsequenceofbendingvibrations.Thisdoubletisnotexhibitedbyn-pentane.
CH3 CC CH3CH3CH2C N
OO
CH3
CH3
CH3
C OH CH3CH2CH2CH2OH
CH2 CHCH3CH2CH2CH2CH3 CH3CH CH3
CH3 CH3
9
(h)
2-Butanonewouldexhibitastrongtransmittancebandatabout1724cm-1.Thisisnotthecaseforethylmethylether;however,theetherwouldexhibitastrongtransmittancebandbetween1150cm-1–1085cm-1.(i)
Thecarboxylicacid,cyclohexylaceticacid,wouldexhibitabroadtransmittancebandbetween3300cm-1–2500cm-1andanintensetransmittancebandforthecarbonylgroupbetween1720cm-1–1695cm-1.1-Propanolwouldexhibitatransmittancebandbetween3200cm-1–3000cm-1.(j)
2-Methylpropanoicacidwouldexhibitabroadtransmittancebandbetween3300cm-1–2500cm-1andanintensetransmittancebandforthecarbonylgroupbetween1720cm-1–1695cm-1. Theanhydridewouldexhibittwostrongtransmittancebandsat1786cm-1and1724cm-1
CH3
O
CH3CH2CH2CH3CH2C OCH3
O
CCH3CH2CH2OH CH2 OH
CH3
CH3
CH3
CH
CH C
C
O
O
O
H3C
H3C
CHH3C C
O
OH
10
13. SketchtheH1NMRspectrumfor
C C
CH3
O
C
H
H
H
a. b.
C C
CH3
H
H O
H
11
a.
Jisthespacingcoupling;therefore,JachasalargervaluethanJab;JachasalargervaluethanJbc;andJabhasalargervaluethanJbc.
12
b.
Thehydrogenatomsonthemethylgroupwouldappearasadoubletatabout1.2ppm.Thehydrogenatomsonmethinegroupwouldappearasaseptet(amultiplex)fartherdownfield(atapproximately2.8ppm)thanthehydrogenatomsonthemethylenegroup.Thehydrogenatomsonthemethylenegroupwouldappearasadoubletatabout2.3ppm.14. Thearomaofcoffeeis,inpart,relatedtocompoundA,C5H8O2.CompoundAcan
berepresentedbythefollowingtheoreticalH1NMRspectrum.C5H8O2,exhibitsastrongIRtransmittanceat1750cm-1.SuggestastructureforcompoundA.
H1NMRofCompoundA
13
15.2’-deoxyuridine,compoundB,hasthefollowingH1NMRspectrum:
NMRspectrumofcompoundB Assignasmanysignalsasyoucantotheappropriateprotonsin2’-deoxyuridine.Thehydrogenatomsthatmaybedistinguishableare:
O
N
N
H
HH
O
H
H
CH2OH
HH
H
HO
1
234
5
1'
2' 3'
4'
5'
6
Compound B
14
(1) Thetwohydrogenatomsonthecarbon-carbondoublebondlabeled4and5.Thehydrogenatomoncarbon4isadistorteddoubletthatappearsatabout6.2ppm,andthehydrogenatomoncarbon5isadistorteddoubletthatappearsatabout5.6ppm.
(2) Thetwohydrogenatomsonthecarbon2thatappearasasingletatabout5.2ppm.
(3) Thehydrogenatomoncarbon4’thatappearsasadistortedtripletcloseto4.0ppm,andthetwohydrogenatomsoncarbon5’thatappearasadistortedtripletaround3.9ppm.
Theremaininghydrogenatomsaredifficulttoidentifyfromthespectrumbecausetheyexhibitoverlappingsignalsinproximityfields.
16. Determinestructuresfortheproductsofthefollowingpathway:
FollowingistheH1NMRofB:
(CH3)3CCH=CHC(CH3)3
B2H6
C10H23B (infrared spectrum at 2500 cm-1)A
(1) 30% H2O2
(2) H2O
C10H22O
B
15
H1NMRofCompoundB ThestructuralformulaforC10H23Bwouldbe:
ThestructuralformulaforC10H22Owouldbe:
17. Suggeststructuresformoleculesexhibitingthefollowingspectra.Give
rationalesforyouranswersbyexplainingthechemicalshifts,spin-spininteractionsand,ifprovided,theelectricalintegrationforeachspectrum.
(a) DeterminethestructuralformulaforC7H7ClO;thecompoundexhibitsthefollowingspectra:
16
H1NMRforC7H7ClO ElectricalIntegration:2:2:3
ChemicalShifts:Para-substitutedpatternbetween6.9ppm-7.3ppmforadisubstitutedaromaticcompoundinwhichthegroupsattachedtothearomaticnucleusaredifferent.Methylprotonsat3.2ppmsuggeststhatthecarbonatomofthemethylgroupisattachedtoanelectronegativeatom.Spin-spinInteraction:Nospin-spininteractionforthemethylprotons;therefore,theprotonsofthemethylgroupappearasasinglet.Thespin-spininteractionofthearomaticprotonsarecomplicated,butsignalofpara-disubstitutedaromaticprotonsresemblewhatappearstobeaquartet,butaromaticprotonsattachedtothecarbonatomsofpara-disubstitutedaromaticcompoundsresemblewhatappearstobeaquartet,but,inreality,thespin-spininteractionprocessissomewhatmorecomplicated.
17
13CNMRforC7H7ClOThe13CNMRspectrumsuggeststhattherearefivetypesofcarbonsinC7H7ClO.
(1) Analiphaticcarbonatomattachedtoanoxygenatomatabout63ppm(2) Four(4)aromaticcarbonatomsbetween110ppm-170ppm.
Oxygenismoreelectronegativethanchlorine.Thearomaticcarbonatomat159ppmisattachedtoanoxygenatom;thecarbonatomat130ppmisattachedtoachlorineatom;thecarbonatomatabout123ppmisattachedtoacarbonatomadjacenttothecarbonatomattachedtotheoxygenatom;andthecarbonatomatabout118ppmisattachedtothecarbonatomadjacenttothecarbonatomattachedtothechlorineatom.Thedatafromthespectrasuggestthatthestructureisp-chloroanisole.
(b) DeterminethestructuralformulaforC9H9ClO;thecompoundexhibitsthefollowingspectra:
18
H1NMRforC9H9ClO ElectricalIntegration:2:2:2:3
ChemicalShifts:Para-substitutedpatternbetween7.5ppm-8.0ppmforadisubstitutedaromaticcompoundinwhichthegroupsattachedtothearomaticnucleusaredifferent.Thespectrumexhibitsmethylprotonsat1.0ppmandmethyleneprotonsatabout2.6ppm.Thissuggeststhatthemethylenecarbonatomisattachedtoanelectronegativegroup.Spin-spinInteraction:Theprotonsonthecarbonatomofthemethylgrouparesplitintoatriplet.Thetripletsuggeststhatthemethylgroupisattachedtoacarbonatomwithtwoprotonsattached(themethylenegroup).Theprotonsonthecarbonatomofthemethylenegrouparesplitintoaquartet.Thequartetsuggestthatthemethylenegroupisattachedtoacarbonatomwiththreeprotons(themethylgroup).Themethylgroupandthemethylenegroupformanethylgroup,CH3CH2–
19
Theadjacentprotonsofthemethylenegroupwouldexperienceaquartetwithapeakratioof1:3:3:1.
Theadjacentprotonsofthemethylgroupwouldexperienceatripletwithapeakratioof1:2:1.Thespin-spininteractionofthearomaticprotonsarecomplicated,butaromaticprotonsattachedtothecarbonatomsofpara-disubstitutedaromaticcompoundsresemblewhatappearstobeaquartet,but,inreality,thespin-spininteractionprocessissomewhatmorecomplicated.
13CNMRforC9H9ClO
Acarefulanalysisofthe13CNMRspectrumsuggeststhatthereareseventypesofcarbonsinC9H9ClO.
(1) Twoaliphaticcarbonatomsbetween13ppm-38ppm.(2) Onecarbonylcarbonatomat220ppm(3) Four(4)aromaticcarbonatomsbetween110ppm-170ppm.
Thecarbonatomofthemethylgroupisat13ppm.Thecarbonatomofthemethylenegroupisat38ppm.
Chorineismoreelectronegativethanthecarbonylgroup.Thearomaticcarbonatomat138ppmisattachedtoachlorineatom;thecarbonatomat126ppmisattachedtoacarbonylgroup;thecarbonatomat125ppmisadjacenttothecarbonatomattachedtothecarbonylgroup;and
20
thecarbonatomatabout124ppmisattachedtothecarbonatomadjacenttothecarbonatomattachedtothecarbonylgroup.Thedatafromthespectrasuggestthatthestructureisp-chlorophenylethylketone(2-[p-chlorophenyl]-1-propanone).
(c) DeterminethestructuralformulaforC12H14O4,thecompoundexhibitsthefollowingspectra:
H1NMRforC12H14O4 ElectricalIntegration:4:2:3
ChemicalShifts:Para-substitutedappearsapparentatabout8.2ppmforadisubstitutedaromaticcompoundinwhichthegroupsattachedtothearomaticnucleusareidentical.Thespectrumexhibitsmethylprotonsat1.2ppmandmethyleneprotonsatabout3.9ppm.Themethylenecarbonatomisattachedtoastrongelectronegativegroup.Spin-spinInteraction:Theprotonsonthecarbonatomofthemethylgrouparesplitintoatriplet.Thetripletsuggeststhatthemethylgroupisattachedtoacarbonatomwithtwoprotons(amethylenegroup).
21
Theprotonsonthecarbonatomofthemethylenegrouparesplitintoaquartet.Thequartetsuggeststhatthemethylenegroupisattachedtoacarbonatomwiththreeprotons(amethylgroup).Themethylgroupandthemethylenegroupformanethylgroup,CH3CH2–
13CNMRforC12H14O4
Analysisofthe13CNMRspectrumsuggeststhattherearefivetypesofcarbonsinC12H14O4.
(1) Twotypesofaliphaticcarbonatoms-oneat17ppmandtheotherat61ppm.
(2) Carbonylcarbonatomatabout175ppm(3) Two(2)typesofaromaticcarbonatoms-oneat125ppmand
theotherat125ppm.
Thecarbonatomofthemethylgroupisat13ppm.Thecarbonatomofthemethylenegroupisat38ppm.Theshiftat38ppmsuggeststhatoneofthealiphaticgroups,themethylenegroup,isattachedtoanoxygenatom.Thearomaticcarbonatomat135ppmisattachedtoacarbonylgroup;thecarbonatomat125ppmisadjacenttothecarbonatomattachedtothecarbonylgroup.Thedatafromthespectrasuggestthatthestructureisdiethylterephthalate(diethylbenzene-1,4-dicarboxylate).
22
(d) DeterminethestructuralformulaforC5H9O4N,thecompoundexhibitsthefollowingspectra:
H1NMRforC5H9O4N ElectricalIntegration:2:1:3:3
ChemicalShifts:Therearefour(4)typesofprotonsexhibitedbythespectrum.Thesignalsinclude:
(1) Methylprotonsatabout1.2ppm(2) Anothermethylgroupatabout1.4ppm(3) Methineprotonatabout2.6ppm.Themethineprotonisattachedto
anelectronegativeatom(probablynitrogen)(4) Methyleneprotonsatabout4.0ppm.
Spin-spinInteraction:Themethylprotonsat1.2ppmaresplitintoadoublet.Thedoubletsuggeststhatthemethylgroupisattachedtoacarbonatomwithoneprotonattached(amethinegroup).Themethineprotonat2.6ppmissplitintoaquartet.Thissuggestthatthemethineprotonisonacarbonatomattachedtoacarbonatomwiththreeprotons(amethylgroup).Themethylprotonsat1.4ppmaresplitintoatriplet.Thetripletsuggeststhatthemethylgroupisattachedtoacarbonatomwithtwoprotonsattached(amethylenegroup).Themethyleneprotonat4.0ppmissplitintoaquartet.Thissuggeststhatthemethyleneprotonisonacarbonatomattachedtoacarbonatomwiththreeprotons(amethylgroup).Themethylgroupandthemethylenegroupformanethylgroup,CH3CH2-Themethylgroupandthemethinegroupform
23
WheretheXandtheYrepresentatomswithprotonsattached.
13CNMRforC5H9O4N
Analysisofthe13CNMRspectrumsuggeststhattherearefivetypesofcarbonsinC5H9O4N.(1) Fouraliphaticcarbonatoms-oneatabout17ppm;oneatabout18ppm;
oneatabout38ppm;andoneatabout61ppm.(2) Carbonylcarbonatomatabout183ppm
Theshiftat38ppmsuggeststhatoneofthealiphaticgroups,themethinegroup,isattachedtoanitrogenatom.Theshiftat61ppmsuggeststhatoneofthealiphaticgroups,themethylenegroup,isattachedtoanoxygenatom.Thedatafromthespectrasuggestthatthestructureisethyl2-nitropropanoate.
24
(e) DeterminethestructuralformulaforC6H14O,thecompoundexhibitsthefollowingspectra:
H1NMRforC6H14OElectricalIntegration:1:6ChemicalShifts:Therearetwo(2)typesofprotonsexhibitedbythespectrum.Thesignalsinclude:
(1) Methylprotonsatabout1.2ppm(2) Methineprotonatabout3.7ppm.Themethineprotonisattachedto
anelectronegativeatom(oxygen)
Spin-spinInteraction:Themethylprotonsat1.2ppmaresplitintoadoublet.Thedoubletsuggeststhatthemethylgroupisattachedtoacarbonatomwithoneprotonattached(amethinegroup).Themethineprotonsat3.7ppmaresplitintoamultiplet(aseptet).Theseptetsuggeststhatthemethinegroupisattachedtocarbonatomswithsixprotons(twomethylgroups).
25
13CNMRforC6H14OAnalysisofthe13CNMRspectrumsuggeststhattherearetwotypesofcarbonsinC6H14O.(1) Onetypeofcarbonatomatabout21ppm(2) Anothertypeofcarbonatomatabout75ppm
Theshiftat75ppmsuggeststhatthecarbonatomofthemethinegroupisattachedtoanoxygenatom.Thedatafromthespectrasuggestthatthestructureisdiisopropylether.
(f) DeterminethestructuralformulaforC7H12O4,thecompoundexhibitsthefollowingNMRandC-13spectra:
26
H1NMRforC7H12O4
ChemicalShifts:Therearethree(3)typesofprotonsexhibitedbythespectrum.Thesignalsinclude:
(1) Oneatabout1.5ppm(2) Anotheratabout3.4ppm.(3) Thefinaloneat4.0ppm
Thechemicalshiftsat3.4ppmand4.0ppmsuggestthattheprotonsresideoncarbonatomsthatareattachedtoelectronegativeatoms.Spin-spinInteraction:Theprotonsat1.5ppmaresplitintoatriplet.Thetripletsuggeststhattheprotonsareattachedtoacarbonatomthatisattachedtoacarbonatomthathastwoprotonsattached(amethylenegroup).Theprotonsat3.4ppmformasinglet.Therefore,theprotonsexhibitingnospin-spininteraction(asingletsuggeststhattheyareattachedtoacarbonatomthatisattachedtoatomsthatdonothaveprotonsattached).
whereXandYdonothaveprotonsattached
Theprotonsat4.0ppmformaquartet.Thequartetsuggeststhattheprotonsareattachedtoacarbonatomthatisattachedtoacarbonatomthathasthreeprotonsattached(amethylgroup).
27
13CNMRforC7H12O4
Analysisofthe13CNMRspectrumsuggeststhattherearefourtypesofcarbonsinC7H12O4.
(1) Threealiphaticcarbonsat17ppm;39ppm;and61ppmrespectively
(2) Acarbonylcarbonatabout179ppm
Theshiftat61ppmsuggeststhatthecarbonatomisattachedtoanoxygenatom,andtheshiftat39ppmsuggeststhatthecarbonatomisattachedtoacarbonylgroup.Thedatafromthespectrasuggestthatthestructureisdiethylmalonate.
(g) DeterminethestructuralformulaforC4H10O,thecompoundexhibitsthefollowingspectra:
28
H1NMRforC4H10O ElectricalIntegration:2:1:1:6
ChemicalShifts:Therearefour(4)typesofprotonsexhibitedbythespectrum.Thesignalsinclude:
(1) Sixmethylprotonsatabout1.0ppm(2) Amethineprotonatabout1.8ppm.Themethineprotonisattached
toacarbonatomthatisattachedtoanelectronegativeatom(oxygen)(3) Twomethyleneprotonsat3.5ppmthatareattachedtoacarbonatom
attachedtoanoxygenatom.(4) Aprotonattachedtoanoxygenatomat2.9ppm.
Spin-spinInteraction:Themethylprotonsat1.0ppmaresplitintoadoublet.Thedoubletsuggeststhatthemethylgroupisattachedtoacarbonatomwithoneprotonattached(amethinegroup).Themethineprotonsat1.8ppmaresplitintoamultiplet.Themultiplexsuggeststhatthemethinegroupisattachedtocarbonatomswithseveralprotons(inthiscaseabout8protons(twomethylgroupsandamethylenegroup).Themethylenegroupat3.5ppmarespitintoadoublet.Theshiftat2.9ppmisduetotheprotondirectlyattachedtoanoxygenatom.Theprotonsofalcohol(OH)generallyundergorapidexchangewithneighboringmolecules;therefore,theOHshiftisnormallyobservedasasinglet.
29
13CNMRforC4H10O
Analysisofthe13CNMRspectrumsuggeststhattherearethreetypesofcarbonsinC4H10O.Thethreealiphaticcarbonsexhibitchemicalshiftsatapproximately19ppm;32ppm;and72ppmrespectivelyTheshiftat72ppmsuggeststhatthecarbonatomisattachedtoanoxygenatom,andtheshiftat39ppmsuggeststhatthecarbonatomisattachedtoacarbonatomthatisattachedtoanoxygenatom.Thedatafromthespectrasuggestthatthestructureisisobutylalcohol(2-methyl-1-propanol).
(h) DeterminethestructuralformulaforC11H9NO4,thecompoundexhibits
thefollowingspectra(achallengingproblem):
30
protonmagneticspectrum
ElectricalIntegration:4:1:1:3ChemicalShifts:Therearefour(4)typesofprotonsexhibitedbythespectrum.Thesignalsinclude:
(1) methylprotonsat1.7ppm(2) Amethineprotonatabout5.7ppm.Themethineprotonisattached
toacarbonatomthatisattachedtoanelectronegativeatom(oxygen)(3) protononanoxygenatomgivingasignalat2.5ppm(4) Fouraromaticprotonsat8.2ppm.Thereisnospittingofthearomatic
hydrogensbecausetheelectronegativegroupsattachedinaparaarrangementaresimilar,butnotexactlythesame.Suchaphenomenonisfrequentlyobservedinmagneticresonancespectroscopy.
Spin-spinInteraction:Themethylprotonsat1.7ppmaresplitintoadoublet.Thedoubletsuggeststhatthemethylgroupisattachedtoacarbonatomwithoneprotonattached(amethinegroup).Themethineprotonsat5.7ppmaresplitintoaquartet,andeachsignalofthequartetisspitadoubletindicatingthatthesplittingoccurswithdifferentJ-couplingconstants.Theresultingsignalsuggeststhatthemethinegroupisattachedtoacarbonatomwiththreeprotonsattachedandanotheratomwithoneprotonattached.
TMS
δ δδ δ δ0
4
11
3
1.72.55.78.2
31
ThisotheratomindicatedasXinthepartialstructuremustbeoxygen.Therefore,thepartialstructurewouldbe:
Characteristicinfraredabsorptionsatabout:2222cm-13333cm-11751cm-1
Thetransmittancebandat2222cm-1isthecarbon-nitrogentriplebondstretchingvibrationofanitrile.Thetransmittanceband3333cm-1istheO-Hstretchingvibration.Thetransmittanceband1751cm-1istheapartialcarbonylstretchingvibrationofananhydride.Thesedatasuggestthatthestructureis2-hydroxypropanoatep-cyanobenzenoateanhydride.
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18. DeterminethestructureofC7H8Sifthecompoundexhibitsthefollowingspectradata:
H1NMRforC7H8S
13CNMRforC7H8S
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PartialmassspectrumofC7H8S
19. DeterminethestructureofC9H10ifthecompoundexhibitsthefollowingprotonmagneticresonanceandcarbon-13magneticresonancespectra.
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20. DeterminethestructureofC12H14O4ifthecompoundexhibitsthefollowingthefollowingprotonmagneticspectrum:
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21. SuggestareasonablestructureforC8H10fromits13CNMRspectrum,its13CNMRDEPT-45spectrum,its13CNMRDEPT-90spetrum,andits13CNMRDEPT-135spectrum.
The13CNMRspectrumforC8H10
ThespectrasuggestthattherearefivetypesofhydrogenatomsinC8H10.Thesecarbonatomsaremethylcarbonatomsthatappearbetween8-35ppmrelevanttoTMS,andfourkindsofaromaticcarbonatomsthatappearbetween110-170ppmrelevanttoTMS.13CNMRDEPT-45spectrumforC8H10
Thequaternarysignalsvanishin13CNMRDEPT-45spectra;therefore,asignaldisappearsintheDEPT-45spectrumforC8H10indicatingthatthestructurecontainsaquaternarycarbonatom.13CNMRDEPT-90spectrumforC8H10
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13CNMRDEPT-90spectraexhibitnegativephasesformethylandmethylenegroupsandapositivephaseformethinegroups.The13CNMRDEPT-90ofC8H10exhibitanegativephaseat20ppmsuggestingthatC8H10containsamethylgroup.
13CNMRDEPT-135spectrumforC8H10
13CNMRDEPT-135spectraexhibitnegativephasesformethylenegroupsandpositivephasesformethineandmethylgroups.The13CNMRDEPT-135spectrumforC8H10doesnotexhibitanynegativephases.ThissuggeststhatC8H10doesnotcontainmethylenegroups.Therefore,thestructureconsistentwiththeC-13spectradatais:
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m-Xylene(1,3-dimethylbenzene)