solutions to spectroscopy problems, building bridges to knowledge

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.

32

18. DeterminethestructureofC7H8Sifthecompoundexhibitsthefollowingspectradata:

H1NMRforC7H8S

13CNMRforC7H8S

33

PartialmassspectrumofC7H8S

19. DeterminethestructureofC9H10ifthecompoundexhibitsthefollowingprotonmagneticresonanceandcarbon-13magneticresonancespectra.

34

20. DeterminethestructureofC12H14O4ifthecompoundexhibitsthefollowingthefollowingprotonmagneticspectrum:

35

21. SuggestareasonablestructureforC8H10fromits13CNMRspectrum,its13CNMRDEPT-45spectrum,its13CNMRDEPT-90spetrum,andits13CNMRDEPT-135spectrum.

The13CNMRspectrumforC8H10

ThespectrasuggestthattherearefivetypesofhydrogenatomsinC8H10.Thesecarbonatomsaremethylcarbonatomsthatappearbetween8-35ppmrelevanttoTMS,andfourkindsofaromaticcarbonatomsthatappearbetween110-170ppmrelevanttoTMS.13CNMRDEPT-45spectrumforC8H10

Thequaternarysignalsvanishin13CNMRDEPT-45spectra;therefore,asignaldisappearsintheDEPT-45spectrumforC8H10indicatingthatthestructurecontainsaquaternarycarbonatom.13CNMRDEPT-90spectrumforC8H10

36

13CNMRDEPT-90spectraexhibitnegativephasesformethylandmethylenegroupsandapositivephaseformethinegroups.The13CNMRDEPT-90ofC8H10exhibitanegativephaseat20ppmsuggestingthatC8H10containsamethylgroup.

13CNMRDEPT-135spectrumforC8H10

13CNMRDEPT-135spectraexhibitnegativephasesformethylenegroupsandpositivephasesformethineandmethylgroups.The13CNMRDEPT-135spectrumforC8H10doesnotexhibitanynegativephases.ThissuggeststhatC8H10doesnotcontainmethylenegroups.Therefore,thestructureconsistentwiththeC-13spectradatais:

37

m-Xylene(1,3-dimethylbenzene)