Tests
Properties
Hydrocarbons
Melting Spectroscopy
BuildingAToolset
For
TheIdentificationofOrganicCompounds
Physical
Chemical Point
Alkanes
Boiling Point
Alkenes
Density
Alkynes
Solubility
Halides
Refractive Index
Alcohols
Aldehydes
Ketones
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Spectroscopy
Mass
(Molecular Weight)
Ultraviolet/Visual
(Conjugation, Carbonyl)
Infrared
Functional Groups
NMR
(Number, Type, Location
of protons)
Gas Chromatography
(Identity, Mole %)
1
Spectroscopy
SpectroscopyTools
04/22/12
2
Spectroscopy
Spectroscopy
Whencontinuousradiationpassesthrougha
transparentmaterial,someoftheradiationcan
beabsorbed.
Iftheportionthatisnotabsorbedispassed
throughaprism,aspectrumwithgapsis
produced.
04/22/12
TheAbsorptionofElectromagneticRadiation
andtheuseoftheResultingAbsorptionSpectra
toStudytheStructureofOrganicMolecules.
Thisiscalledan:
3
Spectroscopy
EnergyStates
Energyabsorptionbytransparentmaterialsin
anyportionoftheelectromagneticspectrum
causesatomsormoleculestopassfromastate
oflowenergy(groundstate)toastateofhigher
energy(excitedstate).
Thereare3typesofEnergyStates:
Electronic
Vibrational
Spin
04/22/12
4
Spectroscopy
ElectromagneticSpectrum
Cosmic
Ultraviolet
Visible Infrared
Microwave
(Gamma)
Radio
EnergyStatesandtheElectromagneticSpectrum
Electronic
Ultraviolet
Vibrational
Infrared
Spin
04/22/12
XRay
Radio
5
Spectroscopy
High
High
Frequency ( )
Energy (E)
Low
Low
Short
Wavelength ( )
Long
Frequency
1.2 x 1014 Hz
3 x 1019 Hz
3 x 1016 Hz
1.5 x 1015 Hz
3 x 108 Hz
2 x 1013 Hz
3 x 1011 Hz
1 x 109 Hz
6 x 107 Hz
4 x103cm-1
1.25 x104cm-1
Wave Number
1 x109cm-1
Cosmic
&
Ray
1 x107cm-1
X-Ray
0.01 nm
Wavelength
2.5 x104cm-1
5 x104cm-1
667cm-1
Vacuum
UV
10 cm-1
Infrared
200 nm
400 nm
800 nm
Visible
Blue
Red
2.5
3 cm-1
Microwave
1 mm
10 nm
Near
Ultraviolet
04/22/12
0.002 cm-1
0.01 cm-1
Radio
30 cm
1m
Frequency
5m
15
Vibrational
Infrared
Nuclear
Magnetic
Resonance
6
Spectroscopy
Quantization
Theexcitationprocessisquantized,inwhichonlyselected
frequenciesofenergyareabsorbedrepresentingthe
energydifference( E)betweentheexcitedandground
states.
E=[E(excited)E(ground)]=h
=c/
E=hc/
Where:
=Frequency(Hz)
=Wavelength(cm)
04/22/12
c =VelocityofLight(cm/sec)
h =PlancksConstant
7
Spectroscopy
SpectroscopyTypes:
MassSpectrometry(MS)HiEnergyElectronBombardment
UseMolecularWeight,PresenceofNitrogen,Halogens
UltravioletSpectroscopy(UV)ElectronicEnergyStates
UseConjugatedMolecules;CarbonylGroup,NitroGroup
InfraredSpectroscopy(IR)VibrationalEnergyStates
UseFunctionalGroups;CompoundStructure
NuclearMagneticResonance(NMR)NuclearSpinStates
UseThenumber,type,andrelativepositionofprotons
(Hydrogennuclei)andCarbon13nuclei
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8
MassSpectroscopy
Highenergyelectronsbombardorganicmoleculesbreaking
someoralloftheoriginalmoleculesintofragments.
Theprocessusuallyremovesasingleelectrontoproducea
positiveion(cationradical)thatcanbeseparatedinamagnetic
fieldonthebasisofthemass/chargeratio.
Removalofthesingleelectronproducesachargeof+1forthe
cation.
Thus,thecationrepresentstheMolecularWeightoftheoriginal
compoundoranyofthefragmentsthatareproduced.
Themassspectrumproducedisaplotofrelativeabundanceof
thevariousfragments(positivelychargedcationradicals)
versustheMass/Charge(M/Z)ratio.
ThemostintensepeakiscalledtheBasePeak,whichis
arbitrarilysetto100%abundance;allotherpeaksarereported
aspercentagesofabundanceofBasePeak.
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9
MassSpectroscopy
M
Molecule
+
eHigh Energy
Electron
M+
+
2e-
Molecular Ion
(Radical Cation)
M - (H2O and CH2 CH2)
1-Pentanol - MW 88
Base Peak
CH3(CH2)3 CH2OH
M - (H2O and CH3)
Typical
Mass
Spectrum
M - H2 O
CH2OH
Molecular Ion Peak
(M+ 88)
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10
MassSpectroscopy
MolecularIonPeak(M+)
Alwaysthelastpeakontherightsideof
spectrum
Mayormaynotbethebasepeak(usuallynot)!
Largestmass/chargeratio
Abundancecanbequitesmall,i.e.,verysmall
peaks
TheMolecularIonPeakrepresentsthe
MolecularWeightoftheCompound
04/22/12
11
MassSpectroscopy
Methyl Propyl Ketone (C5H10O) (CAS 107-87-9)
+
M 43
(C2C2CH3) lost
Propyl Group
+
M 28
(CH2CH2) lost
+
M 15
(CH3) lost
M
04/22/12
+
86
12
MassSpectroscopy
ThePresenceofNitrogenintheCompound
IftheMass/Charge(m/z)ratiofortheMolecular
IonpeakisOdd,thenthemoleculecontainsan
OddnumberofNitrogenatoms,i.e.,1,3,5,etc.
Note:
AnEvenvaluefortheMass/Charge
ratiocouldrepresentacompoundwith
anevennumberofNitrogenatoms,
i.e.,0,2,4etc.
04/22/12
TheactualpresenceofNitrogeninthecompound
isnotexplicitlyindicatedasitiswithanOdd
valuefortheratio.
13
MassSpectroscopy
HalogensinOrganicCompounds
Mostelementsexistinseveralisotopicforms:
Ex.1H1,2H1,12C6,13C6,35Cl17,37Cl17,79Br35,81Br35
AverageMolecularWeight
TheaveragemolecularweightofAllisotopesofa
givenelementrelativetotheabundanceoftheeach
isotopeinnature
IntegralMolecularWeight
TheNumberofProtonsandNeutronsinaspecificisotope
EachfragmentrepresentedinaMassSpectrumproduces
severalpeakseachrepresentingaparticularisotopic
mixtureoftheelementsinthecompound,i.e.,an
integralmolecularweight.
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14
MassSpectroscopy
ThePresenceofChlorineinaCompound
Thetwo(2)principalChlorineIsotopesinnatureare
Cl35andCl37(2additionalNeutronsinCl37)
TherelativeabundanceratioofCl35toCl37is:
100:32.6or75.8:24.2or 3:1
Therefore,aMoleculecontainingasingleChlorineatom
willshowtwoMassSpectrumMolecularIonpeaks,one
forCl35(M+)andoneforCl37(M+2)
Note:M+2denotes2moreneutronsthanM+
04/22/12
Basedonthenaturalabundanceratioof100/32.6
(about3:1),therelativeintensity(peakheight)ofthe
Cl35peakwillbe3timestheintensityoftheCl37peak
15
MassSpectroscopy
ThePresenceofChlorineinaCompound(Cont)
1-Chloropropane
Molecule contains 1 Chlorine atom resulting in two
Molecular Ion Peaks of about 3:1 relative intensity,
based on the 3:1 natural abundance ratio of
Cl-35 / Cl-37
Molecular Ion Peaks
M+ 78: M+2 80
very small
04/22/12
16
MassSpectroscopy
ThePresenceofBromineinaCompound
Thetwo(2)principalBromineIsotopesinnatureare
Br79andBr81(2additionalNeutronsinBr81)
TherelativeabundanceratioofBr79toBr81is
100:97.1or50.5:49.5or 1:1
04/22/12
MoleculescontainingasingleBromineatomwillalso
showtwomolecularionpeaksoneforBr79(M+)and
oneforBr81M+2
Basedonthenaturalabundanceratioof100/97.1
(about1:1),therelativeintensityoftheBr79peakwill
beaboutthesameastheBr81peak
17
MassSpectroscopy
ThePresenceofBromineinaCompound(Cont)
3-Bromo-1-Propene
Molecule contains 1 Bromine atom resulting in
two Molecular Ion Peaks of about 1:1 relative
intensity, based on the 50.5:49.5 (1:1) natural
abundance ratio of
Br-79 / Br-81
Molecular Ion Peaks
M+ 120; M+2 122
04/22/12
18
MassSpectroscopy
ThePresenceofFluorineinaCompound
Fluorineexistsinnatureprincipallyasasingleisotope
19F9
04/22/12
AcompoundcontaininganynumberofFluorineatoms
willhaveasingleMolecularIonpeak(assumingno
otherHalogenspresent)
19
MassSpectroscopy
MultipleHalogensinaCompound
Compoundscontainingtwo(2)Chlorineatoms
willproducethree(3)MolecularIonpeaks
representingthe3possibleisotope
combinationsofChlorine:
Cl1735Cl17(RelPeakIntensity100.0)
35
Cl1737Cl17(RelPeakIntensity65.3)
35
Cl1737Cl17(RelPeakIntensity10.6)
37
04/22/12
20
MassSpectroscopy
MultipleHalogensinaCompound
Compoundscontainingthree(3)Chlorineatoms
willproducefour(4)MolecularIonpeaks
representingthe4possibleisotope
combinationsforChlorine:
35
Cl1735Cl1735Cl17(RelPeakIntensity
Cl1735Cl1737Cl17(RelPeakIntensity
97.8)
Cl1737Cl1737Cl17(RelPeakIntensity
31.9)
35
35
100.0)
Cl1737Cl1737Cl17(RelPeakIntensity 3.5)
37
04/22/12
21
MassSpectroscopy&Molecular
Formula
InformationfromtheMassSpectrumcanusedto
determinetheMolecularFormulaofacompound
Ex.MolecularIonPeaksM+94;M+296(95)
2MolecularIonPeaks(3:1)suggest:1Chlorineatom
PartialAnalysis:C25.4%;H3.2%
Use95asaveragemolecularweight
Carbon:
Hydrogen:
95x0.254=24.1/12=2Catoms
95x0.032=3.0/1=3Hatoms
95(24+3)=68unresolvedmass
(Useoxygen,nitrogen,halides(ClorBr)toresolvemass)
2Oxygen(16+16)+1Chlorine(35.5) 68
MolecularFormulaC2H3O2Cl
04/22/12
22
MassSpectroscopy
Summary
BasePeak100%abundance
MolecularIonPeakHighestMass/Chargeratio
MolecularIonPeakLastpeak(s)onrightsideofchart
MolecularIonPeakRepresentsMolecularWeightof
compound
MolecularIonPeakIfvalueisOddthecompoundcontains
anoddnumberofNitrogenatoms
MolecularIonPeakIftwopeaksoccurandtherelative
abundanceratiois3:1,thenthecompoundcontainsasingle
Chlorineatom.
04/22/12
FragmentationofOrganicMoleculesbyhighenergyelectrons
MolecularIonPeakIftwopeaksoccurandtherelative
abundancerationis1:1,thenthecompoundcontainsasingle
23
Ultraviolet/Visible(UV)Spectroscopy
UVVisibleSpectrum:190nm800nm
InUltravioletandVisibleSpectroscopy,theenergy
absorptiontransitionsthatoccurarebetweenelectronic
energylevelsofvalenceelectrons,thatis,orbitalsoflower
energyareexcitedtoorbitalsofhigherenergy.
Thus,UV/VisiblespectraoftencalledElectronicSpectra
AllorganiccompoundsabsorbUltravioletlighttosome
degree,butinmanycasesatsuchshortwavelengthsto
makeitsutilityofverylimitedvalueinorganicchemistry.
Forthepurposeofthiscourse,theprimaryuseofUV/Vis
willbetoconfirm:
04/22/12
Thepresenceofconjugatedmolecules,eitheraliphatic
alkenestructuresoraromaticringstructures.
Toalesserdegree,thepresenceoftheCarbonylgroup
24
Ultraviolet/Visible(UV)Spectroscopy
Whenamoleculeabsorbsradiationavalenceelectronis
generallyexcitedfromitshighestoccupiedmolecular
orbital(HOMO)tothelowestunoccupiedmolecularorbital
(LUMO)
Formostmolecules,thelowestenergyorbitalsarethe
sigma()orbitals(bonds)
Theelectronsofsigmabondsaretootightlyboundtobe
promotedbyradiationinthe200700nmregion.
Thereforealkanes,saturatedalcohols,simplealkenes
shownoorverylittleUVabsorption.
Theorbitalsoccupysomewhathigherenergylevels.
Orbitalsthatholdunsharedpairsofelectrons,the
nonbonding(n)orbitals,lieatevenhigherenergies.
Unoccupiedorantibondingorbitals(*and*)havethe
04/22/12
25
Ultraviolet/Visible(UV)Spectroscopy
Chromophores
TheNucleiinmolecules,however,determinethe
strengthwithwhichelectronsareboundtothe
molecule,thus,influencingthespacingbetweenground
andexcitedstates
Thecharacteristicenergyofatransitionandthe
wavelengthofradiationabsorbedarepropertiesofa
groupofatomsratherthantheelectronsthemselves.
Thegroupofatomsproducingsuchanabsorptionis
calledaChromophore.
04/22/12
TheabsorptionofUltravioletradiationresultsfromthe
excitationofelectronsfromgroundtoexcitedstate
Asthestructureofthemolecule(alkane,alkene,alkyne,
alcohol,amine,nitrile,carbonyl,etc.)changes,the
26
Ultraviolet/Visible(UV)Spectroscopy
Radiationintherange190nm800nmcausesvalence
electrons(thosethatparticipateinbonding)tobeexcited
toahigherenergylevel.
Thegroundstateofanorganicmoleculecancontain
valenceelectronsinthreeprincipaltypesofmolecular
orbitals:
(sigma)
(pi)
C:H
C::C
Sigma & pi bonds have
antibonding (unocuupied)
orbitals associated
with them
* & *
n (non-bonding)
04/22/12
27
Ultraviolet/Visible(UV)Spectroscopy
Increasing
Energy
Increasing
Energy
Energy Transition Examples
n
n
*
*
*
*
*
in carbonyl compounds
in oxygen, nitrogen, sulfur, and halogen compounds
in alkenes, alkynes, carbonyl and azo compounds
in carbonyl compounds
in alkanes
* Antibonding (single bonds)
* Antibonding (double bonds)
n
Nonbonding (as in lone electron
pairs or the propenyl (allyl) radical
Bonding (double bonds)
Bonding (single bonds)
Note: Electronic energy levels in aromatic molecules
are more complicated than are presented here.
04/22/12
28
Ultraviolet/Visible(UV)Spectroscopy
Atomsproducesharplinesofabsorption
Moleculeshavemanyexcitedmodesofvibrationand
rotationatroomtemperature.Therotationaland
vibrationallevelsaresuperimposedontheelectronic
levels
Electrontransitionsmayoccurfromanyofseveral
vibrationalandrotationalstatesofoneelectroniclevelto
anyofseveralvibrationalandrotationalstatesofahigher
electroniclevel.
Thus,theUVspectrumofamoleculeconsistsofa broad
bandofabsorptioncenterednearthewavelengthofthe
majortransition,i.e.wheretheradiationhasitsmaximum
absorption(max).
04/22/12
29
Ultraviolet/Visible(UV)Spectroscopy
TheUltravioletVisiblespectrum
isgenerallyrecordedasaplot
ofabsorbanceversus
wavelength;buttheplotis
moreoftenpresentedwiththe
Absorptivity()orlogplotted
ontheordinate(yaxis)andthe
wavelengthplottedonthe
abscissa(xaxis)
Ex:
Cyclohexane
(AConjugatedAromaticMolecule)
WavelengthofMaximum
Absorbance
max230nm
************************
MolarAbsorptivity
04/22/12
Log
15,000cm1
4.2
30
Ultraviolet/Visible(UV)Spectroscopy
The Beer-Lambert Law
The Ultraviolet/Visible Spectrum is a plot of the
Wavelength () in nanometers (nm) over the entire
Ultraviolet / Visible region versus the Absorbance (A) of
the radiation at each wavelength.
A = log (Ir / Is) = C L
Is = Intensity of light through sample solution
Ir = Intensity of incident light passing through
Reference cell
=
Molar Absorptivity (Molar Extinction Coefficient)
A measure of the strength or intensity of the
absorption.
Units l/(mol cm) (m2 x 10-2 /mol)
C=
04/22/12
(mmol/dm3)
Concentration of solute (mol/L) or (g/L) if
molecular mass is unknown
31
Ultraviolet/Visible(UV)Spectroscopy
A=
Cl
= A / (C l )
Values of are usually expressed as Log
band)
10,000 20,000
Aliphatic (single
=
(Log = 4.0
4.3)
bands
10,000
Aromatic (two
= 1,000
(Log = 3.0
4.0)
Carbonyl
04/22/12
compounds
100
= 10
(Log = ~ 2)
32
Ultraviolet/Visible(UV)Spectroscopy
TypicalTransitions&AssociatedWavelengthsofMaximum
AbsorptionandMolarAbsorptivities
Transition
max
(nm)
max
Log
n-Butyl Iodide
n *
257
486
2.7
Acetone
n *
279
15
1.2
Acrolein
*
210
11,500
4.1
(C=C & C=O)
n *
315
14
1.1
1,3-Butadiene
*
217
21,000
4.3
1,3,5-Hexadiene *
258
35,000
4.5
ca 200
255
8,000
215
3.9
2.3
Example
Benzene
(2 transitions)
04/22/12
Ar *
Ar *
33
Ultraviolet/Visible(UV)Spectroscopy
Class
Log
n*
180
2.5
ROR
n*
180
3.5
RNH2
n*
190
3.5
RSH
n*
210
3.0
R2C=CR2
*
175
3.0
RC=CR
*
170
3.0
RC N
n*
160
<1.0
RN=NR
n*
340
1.0
RNO2
n*
271
<1.0
RCHO
*
190
2.0
RCHO
n*
290
1.0
R2CO
*
180
3.0
R2CO
n*
280
1.5
RCOOH
n*
205
1.5
RCOOR
04/22/12
max(nm)
ROH
TypicalTransitions
andAbsorptions
ofSimpleIsolated
Chromophores
Transition
n*
205
1.5
RCONH2
n*
210
1.5
34
Ultraviolet/Visible(UV)Spectroscopy
ComputationExample:
Anunsaturatedketoneofrelativemolecularweight
110hasanabsorptionbandwithmaxat215nmand=
10,000(l/molcm)
AsolutionofthisketoneshowedabsorbanceA=2.0
witha1cmcell.Calculatetheconcentrationofthe
ketoneinthissolutionexpressedingramsperliter.
Ans: A=cL
c=A/L
c=2.0/((10,000l/molcm)*1.0cm)
c=2x104mol/l
c=2x104mol/lx110g/mol
04/22/12
c=2.20x102g/l
35
Ultraviolet/Visible(UV)Spectroscopy
ComputationExample:
CalculatetheMolarAbsorptivity,,forasolutioncontaining1.0
mmoldm3(1.0x103molesperliter)ofsolute,whenthe
absorbanceofa1cmcellwas1.5.
Ans:
A
=cL
=A/cL
=1.5/(1x103mol/L)(1cm)
=1.5x103L/molcm
WhatwouldbetheAbsorbanceforasolutionofdoublethis
concentration?
Ans:
04/22/12
A
A
=3.0
=1.5x103L/molcm2.0x103moles/L1cm
36
Ultraviolet/Visible(UV)Spectroscopy
Alkanes
Containsinglesigmabondsresultinginonly*
transitionswhichabsorbultravioletradiationat
wavelengthsgenerallytooshortforuseinUV
spectroscopy.
Utility:None
Alcohols,Ethers,Amines,SulfurCompounds
Then*transitionsabsorbUVradiationwithinthe
experimentallyaccessiblerange(>180nm).
Utility:Verylittle
04/22/12
37
Ultraviolet/Visible(UV)Spectroscopy
AlkenesandAlkynes
AbsorbUVradiationintherange<180nm.
Cumulatedalkenes(*transitions),whichhave
oneormoresigmabondsbetweenthedouble
boundsusuallyhaveabsorptionmaximabelow200nm.
Utility:Verylittle
CompoundswithOxygendoublebonds
Unsaturatedmoleculescontainingoxygenornitrogen
structuressuchasCarbonyl(C=O)andNitro(NO2)
havebothn*(280290nm)and*transitions
(188nm).
Utility:Moderate
04/22/12
38
Ultraviolet/Visible(UV)Spectroscopy
Conjugatedunsaturatedsystemsaremoleculeswithtwoor
moredoubleortriple()bondseachalternatingwithasingle
orsigmabond().
Conjugatedunsaturatedsystemshavedelocalizedbonds,
i.e.,aporbitalonanatomadjacenttoadoublebond
producing*transitions.
Vacantporbitalasinallylcation(CH2=CHCH2+)
Singleelectronasintheallylradical(CH2=CHCH2)
Porbitalofanotherdoublebond(CH2=CHCH=CH2
ConjugatedsystemsincludetheAliphaticAlkenesaswellas
theAromaticringstructures.
Compoundswhosemoleculescontainconjugatedmultiple
bondsabsorbstronglyintheUV/Visibleportionofthe
electromagneticspectrum(>200nm).
04/22/12
39
Ultraviolet/Visible(UV)Spectroscopy
ConjugatedUnsaturatedSystems
Conjugatedsystemsconsistofalternatingsigma()bonds
andpi()bonds)andtheUltravioletabsorptionsshow
largevaluesof
2,5-Dimethyl-2,4-Hexadiene (in Methanol)
The Wavelength of Maximum Absorption ( max ) is obtained
from the Absorption Spectrum
Wavelength of Maximum Absorbance (max) 242.5 nm
Molar Absorptivity ( ) 13,100 M-1 cm-1 (Log = 4.1)
04/22/12
40
Ultraviolet/Visible(UV)Spectroscopy
ConjugatedUnsaturatedSystems(Cont)
,Unsaturatedketones,Dienes,Polyenes
Transitions
*
HighIntensityBands
=10,000to20,000(log=4.04.3)
max>210nm
AromaticConjugatedSystems
Transitions *
2MediumIntensityBands
=100060,000(log=3.04.8)
maxbothbands>200nm
Note: SubstitutiononringincreasesMolarAbsorptivityabove
04/22/12 10,000
41
Ultraviolet/Visible(UV)Spectroscopy
Carbonyl(C=O),NitroGroup(NO2)(Resonanceeffectson
substitutedbenzene)
Transitions
n*&*
SingleLowIntensityBand =10 (log=1)to
=300 (log=2.5)
max(250360nm)
Nitro(NO2)
log(~1.0)
Carbonyl(C=O)
log(~2.0)
Thepresenceofthesefunctionalgroupsshouldbeused
onlyasconfirmationsofspeciesidentifiedintheIR
Spectra.
04/22/12
42
Ultraviolet/Visible(UV)Spectroscopy
PracticalApproachtoInterpretingUV/VisInformation
IftheproblemyouareworkingonprovidesanUV/Vis
spectrumanditindicatesNoabsorptioninthe200700nm
range,thefollowingconclusionsareapplicable:
Thecompoundisnotconjugated,i.e.,itdoesnotcontain
alternatingdouble/singlebonds(includingBenzenering.)
ThecompoundprobablydoesnotcontainCarbonylor
Nitrogroups(confirmwithIR).
IftheproblemprovidesLogAbsorptivityvalues(Log)the
followingpossibilitiesexist:
Log(>4.0)
Conjugated
Log(3.04.0)
Aromaticring
,Unsaturated
ketones,Dienes,Polyenes
04/22/12
43
InfraredSpectroscopy
InfraredSpectroscopyReferences
pp.873909
Pavia,etal
Solomonsetal
pp.7984;821822;
InfraredRadiation
Thatpartoftheelectromagneticspectrumbetweenthe
visibleandmicrowaveregions
0.8m(12,500cm1)to50m(200cm1).
AreaofInterestinInfraredSpectroscopy
TheVibrationalportionofinfraredspectrum
2.5m(4,000cm1)to25m(400cm1)
04/22/12
Radiationinthevibrationalinfraredregionisexpressedin
44
InfraredSpectroscopy
Wavenumbersareexpressedinunitsofreciprocal
centimeters(cm1)i.e.thereciprocalofthewavelength()
expressedincentimeters.
(cm1)=1/(cm)
WaveNumberscanbeconvertedtoafrequency()by
multiplyingthembythespeedoflight(c)incm/sec
(Hz)=c=c/(cm/sec/cm=1/sec)
Recall:E=hc/
04/22/12
Thus,wavenumbersaredirectlyproportionaltoenergy
45
InfraredSpectroscopy
PolarCovalentBonds&DipoleMoments
TheElectronsbetweenatomsinanorganiccompound
aresharedformingCovalentbonds.
Covalentbondsbetweenatomswithdifferent
electronegativitieshaveanunequalsharingofthebond
electronssettingupanelectrostaticchargedifference
betweentheatoms.
04/22/12
Organiccompoundsareorganizedintofamiliesof
compoundsonthebasisofcertaingroupingsofatoms,
i.e.,FunctionalGroups.
TheatomwiththegreaterElectronegativitypullsthe
electronsclosertoitformingaPolarCovalentBond.
46
InfraredSpectroscopy
PolarCovalentBonds&DipoleMoments(Cont)
Theseparationofthepositiveandnegativechargesina
PolarCovalentBondisreferredtoasaDipole.
AdipolehasaDipoleMomentdefinedastheproductof
themagnitudeofthepartialcharges(inelectrostatic
units,esu)timesthedistance(incm)ofseparation.
04/22/12
TherelativestrengthofthePolarCovalentBondimpacts
theabilityofthemolecule,i.e.,aFunctionalGroup,to
attractorrepelotherpolarentities(functionalgroups).
OnlythoseCovalentbondswithDipoleMomentsare
capableofabsorbingInfraredRadiation.
47
InfraredSpectroscopy
TheRadiation(Energy)AbsorptionProcess
ThisisaQuantizedprocessinwhichonlyselected
frequenciesareabsorbeddependentontherelative
massesoftheatoms,theforceconstantsofthebond
(electronegativity),andthegeometryoftheatoms.
CovalentBondspossessRotationalandVibrational
frequencies.
Everytypeofbondhasanaturalfrequencyofvibration.
04/22/12
TheabsorptionofInfraredRadiationbyaPolar
CovalentBondraisesthemoleculetoahigherenergy
state.
Thesamebondindifferentcompoundshasaslightly
differentfrequencyofvibration.
48
InfraredSpectroscopy
WhenthefrequenciesofInfraredRadiationmatchthe
naturalvibrationalfrequenciesofabondwithaDipole
Moment,theradiationisabsorbedincreasingthe
amplitudeofthevibrationalmotionsofthecovalentbonds.
Infraredradiationisabsorbedandconvertedbyorganic
moleculeswithpolarcovalentbondsanddipolemoments
intoenergyofmolecularrotationandmolecularvibration.
RotationLessthan100cm1(Spectrumislines)
Vibration10,000cm1to100cm1(Spectrumisbands)
Thevibrationalbandsappearsbecauseeachvibrational
energychangeisaccompaniedbyanumberofrotational
changes
InfraredSpectroscopyisconcernedonlywiththe
vibrationalspectrum(4,000cm1to400cm1)
04/22/12
49
InfraredSpectroscopy
MolecularVibrations
Absorptionofinfraredradiationcorrespondstoenergy
changesontheorderof840KJ/mole(210Kcal/mole
Thefrequenciesinthisenergyrangecorrespondtothe
stretchingandbendingfrequenciesofthecovalent
bondswithdipolemoments.
Stretching(requiresmoreenergythanbending)
Symmetrical
Asymmetrical
Bending
(inplanebending)
04/22/12
Scissoring
Rocking
(inplanebending)
Wagging
(outofplanebending)
50
InfraredSpectroscopy
StretchingArhythmicalmovementalongthebondaxis
suchthattheinteratomicdistanceisincreasingor
decreasing.
Inanygroupofthreeormoreatomsatleasttwoof
whichareidenticaltherearetwomodesofstretchingor
bending:SymmetricandAsymmetric
FortheMethyleneGroup(CH2):
CH
H
C
H
Symmetric
Stretch
(2853 cm-1)
04/22/12
H
C
H
Asymmetric
Stretch
(2926 cm-1)
51
InfraredSpectroscopy
BendingAchangeinbondanglebetweenbondswitha
commonatomor
Amovementofagroupofatomswithrespecttothe
remainderofthemolecule
H
Wagging
~1250 cm-1
(In Plane)
H
(Out of Plane)
Rocking
~750 cm-1
H
Twisting
~1250 cm-1
(Out of Plane)
Scissoring
~1450 cm-1
(In Plane)
04/22/12
C
C
H
H
H
C
H
H
C
52
InfraredSpectroscopy
Thus,notwomoleculesofdifferentstructurewillhave
exactlythesamenaturalfrequencyofvibration,eachwill
haveauniqueinfraredabsorptionpatternorspectrum.
TwoUses:
04/22/12
IRcanbeusedtodistinguishonecompoundfrom
another.
AbsorptionofIRenergybyorganiccompoundswill
occurinamannercharacteristicoftherelativestrengths
ofthePolarCovalentBondsintheFunctionalGroups
presentinthecompound;thus,anInfraredSpectrum
givesstructuralinformationaboutthefunctionalgroups
presentinamolecule.
Theabsorptionsofeachtypeofbond(NH,CH,OH,
CX,C=O,CO,CC,C=C,CC,CN,etc.)are
regularlyfoundonlyincertainsmallportionsofthe
53
InfraredSpectroscopy
Instrumentation
Dispersive(DoubleBeam)IRSpectrophotometer
Split
Beams
Air
Detector
IR Source
Lenz
Slit
Recorder
Sample
Monochromator
ThesplitbeamspassintoaMonochromator,whichconsistsofarapidly
rotatingsectorthatpasseseachbeamtoadiffractiongratingorprism.
Theslowlyrotatingdiffractiongratingvariesthewavelengthofradiation
reachingthedetector.
Thedetectorsensestheratioinintensitybetweenthereference(air)and
samplebeamsandrecordsthedifferencesonachart.
04/22/12
54
InfraredSpectroscopy
SamplePreparation
LiquidSamples
1to2dropsofliquidsampleareplacedbetweentwo
singlecrystalsofsodiumchloride(Plates)
Note:NaCLplatesarewatersolublekeepdry
SolidSamplessolubleinAcetone
Dissolvesampleinacetone
EvaporateonSaltPlate
SolidSamplesnotsolubleinacetone
MakePotassiumBromide(KBR)pellet
04/22/12
Putplatesinplateholder
PlaceholderinIRSpectrometer
55
InfraredSpectroscopy
FourierTransform(FT)SingleBeamIR
Setbackground(air)
PressBackgroundbutton
VerifyNo.ofScansis4;ifnot,pushsoftkeytoset
4
PressScanbutton
PressExecute
ObtainSampleSpectra
PressSCANbutton
SelectMemorylocation(X,Y,orZ)
04/22/12
InsertCellHolderintobeamslot
PressExecute
56
InfraredSpectroscopy
ourierTransform(FT)SingleBeamIR(Cont)
RerunScanagain
PushPlottoproducechart
RemoveCellHolderanddisassemble
04/22/12
Ifspectrumbottomsout(mighthavetocheckwith
instructor),thenremoveCellHolder;removetopofSalt
Plate;wipelightlywithtissue;reassemble;andinsert
cellholderintobeamslot.
CleanSaltPlate;dry;returntoinstructor;placein
desiccator
57
InfraredSpectroscopy
TheInfraredSpectrum
Aplotofabsorptionintensity(%Transmittance)onthe
yaxisvs.frequencyonthexaxis.
Transmittance(T)theratiooftheradiantpower
transmittedbyasampletotheradiantpowerincidenton
thesample.
Absorbance(A)thelogarithmtobase10ofthe
reciprocaloftheTransmittance.
A=log10(1/T)
Wavelength
04/22/12
FrequencyThexaxisisrepresentedbytwoscales:
Wavenumber (4000cm1to400cm1)
(2.5to25)
(Bottom)
(Upper)
58
InfraredSpectroscopy
IRSpectrum
Ketone
C=O
Carbonyl
Overtone
CH2
Aliphatic
C-H Stretch
C5H10O
04/22/12
C=O
Carbonyl
CH3
MethylIsopropyl
Ketone
CAS 563-80-4
59
InfraredSpectroscopy
IRSpectrumPeakCharacteristics
PrimaryExaminationRegionsoftheSpectrum
4000to1300cm1
HighFrequencyRegion
Intermediate(FingerprintRegion)
1300to900cm1
HighFrequencyRegion(FunctionalGroupRegion)
CharacteristicStretchingfrequenciesofsuchgroupsas:
=CH,OH,NH,C=O,CO,CN,CC,C=C
TheFingerprintRegion1300to900cm1
Bandsoriginatefrominteractingvibrationalmodes
Valuablewhenusedinreferencetootherregions
04/22/12
Absorptionpatternsfrequentlycomplex
Absorptionuniqueforeverymolecularspecies
Effectiveusecomesfromexperience
60
InfraredSpectroscopy
RSpectrumPeakCharacteristics(cont)
Shape
Sharp(narrow)
Broad
Intensity
(w)
Medium
(m)
04/22/12
Weak
Strong
(s)
ote:
Peakintensityisdependentonamountofsample
andsensitivityofinstrument;therefore,theactual
intensitycanvaryfromspectrumtospectrum
61
InfraredSpectroscopy
PrincipalFrequencyBands
OH
3600cm1
(Acids,Alcohols)
NH
33003500cm1 (Amino)
(1o2peaks,2o1peak,3o0peaks)
CN 2250cm1
(Nitrile)
CC 2150cm1
(Acetylene)
CCH
C=O 16851725cm1
C=C 1650cm1
04/22/12
NO2
14501650cm1 (2absorptions)
C=C 14501600cm1 (Aromatic)4absorptions
3300cm1 (TerminalAcetylene)
(Carbonyl)
(Alkene)2absorptions
62
InfraredSpectroscopy
rincipalFrequencyBands(Cont)
CH2
1450cm1
(Methylene)
CH3
1375&1450cm1
(Methyl)
CH Rightsideof3000cm1(SaturatedAlkane)
=CH Leftsideof3000cm1(UnsaturatedAlkene)
=CH 16672000cm1(AromaticOvertones)
04/22/12
CO 9001100cm1 (Alcohol,Acid,Ester,
Ether,Anhydride)
CH 2150cm1(Stretch)
63
InfraredSpectroscopy
Functional
Group
Typeof
Vibration
Frequency
cm1 Intensity
Alkanes(CH)
(stretch)
30002850
s
CH3
(bend)
1450&1375
m
CH2
(bend)
1465
m
Alkenes(C=C)
(stretch)
31003000
m
(bend)
1000650
s
(stretch)
31503050
s
(OOPbend)
1000650
s
Alkyne(C )
(stretch)
3300
s
Aldehyde(CHO)
(stretch)
29002800
w
Aromatics
04/22/12
64
InfraredSpectroscopy
CorrelationTable
FunctionalGroup Frequency(cm1)
CC
C=C
mw
Aromatic
mw
CC
mw
CCH
C=O
04/22/12
Ester
s
Alkane
Alkene
Intensity
NotUseful
16801600
16001400
Alkyne
Alkyne(terminal)
Anhydride
22502100
3300
s
~1810 s
~1760 s
17501730
65
InfraredSpectroscopy
CorrelationTable
FunctionalGroup Frequency(cm1)Intensity
CO Alcohols,Ethers13001000s
Esters,Acids
OH Alcohols,Phenols
Free36503600m
HBonded34003200m
CarboxylicAcids
33002500m
NH Primary&SecAmines~3500 m
CN Nitriles22602240m
N=O Nitro(RNO2)16001500s
14001300 s
CX Fluoride14001000s
04/22/12
66
InfraredSpectroscopy
AnalyzingtheSpectrumASuggestedApproach
Step1. CheckforthepresenceoftheCarbonylgroup
(C=O)in
therange16601820cm1.
IftheCarbonylGroupispresent,oneofthe
typesofcompoundsispresent:
CarboxylicAcid
Ester
Amide
Anhydride
Aldehyde
Ketone
following
AcidChloride
Ifthemoleculeisconjugated(alternating double&single
04/22/12
67
InfraredSpectroscopy
AnalyzingtheSpectrumASuggestedApproach
Step2.CheckforthepresenceofSaturatedAlkane
structures
CompoundscontainingjustMethyl(CH3)&Methylene(CH2)
groupsproducegenerallysimpleIRspectra
CHsp3absorptionisastretchintherange30002840
cm1
Note:
ItisimportanttorememberthattheAlkanesp3
stretch
occursontherightsideofthe3000cm1markinthe
IRspectrumandthatAlkeneandAromatic
sp2
stretchesoccurontheleft
sideofthe3000cm1mark
(seenext
slide).
04/22/12
CH3
Methylgroups(CH3)haveacharacteristicbending
68
InfraredSpectroscopy
AnalyzingtheSpectrumASuggestedApproach
Step3. Checkforthepresenceofunsaturated(=CH)sp2
structures.
=CHsp2absorptionisastretchintherange3000
3100cm1,i.e.,ontheleftsideofthe3000cm1
mark
onthexaxisscale.
Step4. Determinewhetherthe=CHbondisAliphatic
Alkene,Aromatic,orboth.
ForAlkene=CHbonds,lookfortheC=Cstretchat
16001650cm1,usuallyanunequalpairof absorptions.
OutofPlan(OOP)bendingat6501000cm1
04/22/12
Note:
Seenextslideorthetableonpage895of
Pavia
textforguidetosubstitution
patternson
substituted
69
InfraredSpectroscopy
AnalyzingtheSpectrumASuggestedApproach
04/22/12
OutofPlane(OOP)substitutionpatterns(substitutedalkenes)
70
InfraredSpectroscopy
IRSpectrum
AliphaticAlkene
1-Hexene
CH3
Unsat
=C-H Stretch
CH2
Satd
-C-H Stretch
04/22/12
C6H12
Aliphatic
C=C
Stretch
OOP Bending
Monosubstitution
CAS 592-41-6
71
InfraredSpectroscopy
AnalyzingtheSpectrumASuggestedApproach
Step4(Cont)
Aromatic=CHbonds.
LookforC=Cstretch(pairofabsorptionsat1450cm1
andapairofabsorptionsat1650cm1
Overtone/Combinationbandsappearbetween
1667&2000cm1
OutofPlain(OOP)bendingbetween6501000cm1
Note:
Seenextslideorthetableonpage897of
Paviatext
forguidetosubstitutionpatternsonBenzene
ring.
Note: Thesubstitutionpatterninformationinthe
OvertoneareaandtheOOPareais
04/22/12
72
InfraredSpectroscopy
OOP Substitution Patterns (Aromatic)
Overtone Area Substitution Patterns
(Aromatic)
04/22/12
73
InfraredSpectroscopy
IRSpectrum
(Aromatic)
Toluene (Methyl Benzene)
Aromatic
Overtones
Mono-Substitution
Unsatd
CH3
Satn
Aromatic
C=C
Stretch
C7H8
04/22/12
OOP Bending
Mono-Substitution
CAS 108-88-3
74
InfraredSpectroscopy
AnalyzingtheSpectrumASuggestedApproach
StrongbandofC=Ogroupappearsinrange17001725cm1.
VerybroadabsorptionbandoftheOHgroupintherange
24003400cm1.
ThisbroadbandwillusuallyobscuretheAlkaneCHstretch
bandsfrom28493000cm1.
04/22/12
Step5.CarbonylCompounds(CarboxylicAcids)
MediumintensityCOstretch(asinCOH)occursinthe
range12101320cm1
75
InfraredSpectroscopy
IRSpectrum
CarboxylicAcids
Isobutyric Acid
CH3
OH Stretch
sp3 C-H
Stretch
C4H8O2
04/22/12
C=O
Carbonyl
C-O
CAS 79-31-2
76
InfraredSpectroscopy
AnalyzingtheSpectrumASuggestedApproach
Step6.CarbonylCompounds(Esters)
04/22/12
C=Ostretchappearsintherange17301750cm1
Checkfor2ormoreCOstretchbands,onestrongerand
broaderthantheother,intherange11001300cm1
77
InfraredSpectroscopy
IRSpectrum
Esters
Methyl Benzoate
Aromatic
Overtones
Unsatd
=C-H Stretch
Aliphatic
C-H Stretch
Aromatic Ring
C=C Absorptions
C-O
C=O
Carbonyl
C8H8O2
04/22/12
C-O
Aromatic
OOP
CAS 93-58-3
78
InfraredSpectroscopy
AnalyzingtheSpectrumASuggestedApproach
Step7.CarbonylCompounds(Anhydrides)
Conjugationwillmovethesebandstolowerfrequency
04/22/12
2C=Ostretchbands(17401775cm1&18001830cm1)
MultipleCOstretchbandsintherange9001300cm1
79
InfraredSpectroscopy
IRSpectrum
Anhydrides
Propionic Anhydride
C=O
Overtone
C-H
Aliphatic
Stretch
CH2
Pair of
C=O
Stretch bands
C6H10O3
04/22/12
CH3
C-O Stretch
CAS 123-62-6
80
InfraredSpectroscopy
AnalyzingtheSpectrumASuggestedApproach
Step8.CarbonylCompounds(Amides)
C=Ostretchatapproximately16401700cm1
NHstretch(mediumabsorptions)near3500cm1
PrimaryAmino(NH2)
2Peaks(3180&3350
SecondaryAmino(NH)
1Peak(3300cm1)
cm1)
15501640cm1
04/22/12
NHScissoring
NHBend
800cm1
81
InfraredSpectroscopy
IRSpectrum
Amides
Benzamide
Aromatic
Overtones
Unsatd
=C-H Stretch
NH2 Stretch
2 peaks
Primary Amino
N-H
Scissoring
C=O
Carbonyl
C7H7NO
04/22/12
{
-C-N str
C=C
Aromatic
CAS 55-21-0
82
InfraredSpectroscopy
IRSpectrum
Amides
Acetanilide
(N-Phenylacetamide)
Unsatd
=C-H Stretch
Aromatic
Overtones
NH Stretch
1 Peak
Sec Amino
N-H
Bend
C=O
Carbonyl
C8H9NO
04/22/12
OOP Bend
Aromatic
Monosubstitution
{
CH3
C=C
Aromatic
CAS 103-84-4
83
InfraredSpectroscopy
AnalyzingtheSpectrumASuggestedApproach
C=Ostretchappearsintherange17201740cm1
04/22/12
Step9.CarbonylCompounds(Aldehydes)
2weakAldehydeCHstretchabsorptionsnear2850and
2750cm1)
84
InfraredSpectroscopy
IRSpectrum
Aldehydes
Nonanal
C=O
Overtone
CH3
Aldehyde
Hydrogen
Stretch
2 Peaks
Aliphatic
C-H Stretch
04/22/12
C9H18O
CH2
C=O
Carbonyl
CAS 124-19-6
85
InfraredSpectroscopy
AnalyzingtheSpectrumASuggestedApproach
Step10.CarbonylCompounds(Ketones)
C=Ostretchoccursatapproximately17051725cm1
Ketonesareconfirmedwhentheotherfivecompoundtypes
containingaCarbonylgrouphavebeeneliminated.
KetoneIRSpectracansometimesbeconfusedwithEster
spectrabecauseofanabsorptioninthe11001300cm1
rangesimilartothelocationoftheCOstretchinesters.
Usually,however,theesterwillhave2ormoreoftheCO
stretchabsorptions.
TheKetonestructureproducesa
mediumtostrongabsorptionin
the11001300cm1rangedue
tocoupledStretchingand
Bendingvibrations
04/22/12
86
InfraredSpectroscopy
IRSpectrum
Ketones
Ethyl Isopropyl Ketone
(2-Methyl-3-Pentanone)
C=O
Overtone
Aliphatic
C-H Stretch
C6H12O
04/22/12
C=O
Carbonyl
CH2
CH3
CAS 565-69-5
87
InfraredSpectroscopy
AnalyzingtheSpectrumASuggestedApproach
Step11.TripleBonds
Alkynes
RCCR
weak,sharpstretchnear2150cm1
RCCH
(TerminalAcetylene)
Weak,sharpstretchnear2150cm1
andasecondstretchat3300cm1
Nitriles
CN
04/22/12
Medium,sharpstretchnear2250cm1
88
InfraredSpectroscopy
IR Spectrum
Alkynes (C C)
Propargyl Alcohol
(2-Propyn-1-ol)
CC
Stretch
OH
H - Bonded
Aliphatic
C-H Stretch
C-H Terminal Alkyne
Stretch
C3H4O
04/22/12
CH2
C-O
CAS 107-19-7
89
InfraredSpectroscopy
IR Spectrum
Nitriles
Benzonitrile
Aromatic
Overtones
Unsat
=C-H Stretch
-CN
Stretch
C7H5N
04/22/12
Aromatic ring
C=C Absorptions
Aromatic
OOP Bending
Monosubstitution
CAS 100-47-0
90
InfraredSpectroscopy
AnalyzingtheSpectrumASuggestedApproach
Step12.Alcohols&Phenols
04/22/12
Broadabsorptionnear36003300cm1
ConfirmpresenceofCO(COH)near10001300cm1
91
InfraredSpectroscopy
IR Spectrum
Alcohols & Phenols
2-Naphthol (Nujol Mull)
Unsaturation
=C-H Stretch
OH
H - Bonded
Saturation
-C-H Stretch
Aromatic ring
C=C Absorptions
C10H9O
04/22/12
CAS 135-19-3
92
InfraredSpectroscopy
IR Spectrum
Alcohols & Phenols
2-Naphthol (CCl4 Soln)
Unsat
=C-H Stretch
OH
H - Bonded
C10H9O
04/22/12
Aromatic ring
C=C Absorptions
C-O
CAS 135-19-3
93
InfraredSpectroscopy
IR Spectrum
Alcohols & Phenols
2-Naphthol (KBr Disc)
Unsat
=C-H Stretch
OH
H - Bonded
C10H9O
04/22/12
Aromatic ring
C=C Absorptions
C-O
CAS 135-19-3
94
InfraredSpectroscopy
IR Spectrum
Alcohols & Phenols
2-Butanol
CH2 CH3
OH
C4H10O
04/22/12
C-O
Aliphatic
C-H Stretch
CAS 78-92-2
95
InfraredSpectroscopy
AnalyzingtheSpectrumASuggestedApproach
Step13.Ethers
AbsenceofOH
AbsenceofC=Ogroup
AliphaticEthersgiveasinglestrongCObandat
1120cm1
UnbalancedEtherswillshow2COgroups
04/22/12
COabsorptionsnear10001300cm1
PhenylAlkylEthersgivetwo(2)strongbandsatabout
1040&1250cm1
96
InfraredSpectroscopy
IR Spectrum
Ethers
Butyl Ether
(Balanced Ether)
CH3
CH2
Aliphatic
C-H Stretch
C8H18O
04/22/12
CH3(CH2)3 O (CH2)3CH3
C-O
CAS 142-96-1
97
InfraredSpectroscopy
IR Spectrum
Ethers
Unsat
=C-H Stretch
Phenetole
(Unbalanced Phenyl Alkyl Ether)
Aromatic
Overtones
Aliphatic
C-H Stretch
CH3
C-O
CH2
Aromatic ring
C=C Absorptions
04/22/12
C8H10O
C-O
OOP Bending
Aromatic
Monosubstitution
CAS 103-73-1
98
InfraredSpectroscopy
AnalyzingtheSpectrumASuggestedApproach
Step14.Amines
NHstretch(Mediumabsorptions)near3500cm1
PrimaryAmino 2Peaks
SecondaryAmino
TertiaryAmino
1Peak
Nopeaks
04/22/12
NHScissoringat15601640cm1
NHBendat800cm1
99
InfraredSpectroscopy
n-Butylamine
IR Spectrum
Amines
(Primary Amine)
-C-N
Stretch
N-H
Scissoring
CH3
H-N-H Stretch
2 Peaks
Primary Amine
CH2
Aliphatic
(satn)
C-H Stretch
C4H11N
04/22/12
-N-H
OOP Bending
CAS 109-73-9
100
InfraredSpectroscopy
IR Spectrum
Amines
N-Methylbenzylamine
(Sec Amine)
Aromatic
Overtones
N-H
Scissoring
Sec-Amino
Unsat
=C-H Stretch
Sat
C-H Stretch
Aromatic ring
C=C Absorptions
N-H
Scissoring
Aliphatic
C-H Stretch
C6H11N
04/22/12
CH3
CH3
-N-H
OOP Bending
C-N Str
CH2
CH2
OOP Bending
Aromatic
Monosubstitution
CAS 103-67-3
101
InfraredSpectroscopy
AnalyzingtheSpectrumASuggestedApproach
Step15.NitroCompounds
Twostrongabsorptions
AliphaticNitroCompounds
Asymmetricstrongstretch
cm1
1300
1390
Asymmetricstrongstretch
cm1
04/22/12
1600
Symmetricmediumstretch
cm1
1530
1490
1550
Symmetricstrongstretch
cm1
1315
1355
AromaticNitroCompounds
102
InfraredSpectroscopy
IR Spectrum
Nitro Compounds
Nitro Benzene
Aromatic
Overtones
Mono-Substitution
Unsat
=C-H Stretch
C=C
Aromatic ring
Absorptions
NO2 (-N=O) Stretch
2 Absorptions
C6H5NO2
04/22/12
CAS 98-95-3
103
InfraredSpectroscopy
IR Spectrum
Nitro Compounds
1-Nitro Propane
Aliphatic
C-H Stretch
NO2 (-N=O) Stretch
2 Absorptions
04/22/12
C3H5NO2
CAS 108-03-2
104
InfraredSpectroscopy
Step16.Ifnoneoftheaboveapplythenthecompoundis
mostlikelya:
Hydrocarbon
AlkylHalide(seeslides105109).
Hydrocarbons
CHSatdAlkanes
29003000cm1
Methyl(CH3)
1370cm1
Methylene(CH2)
1450cm1
04/22/12
Generally,verysimplespectrum
tButylGroup
525cm1
105
InfraredSpectroscopy
IR Spectrum
Alkane
Decane
CH3
Long Alkane
Chain (CH2)
Bending
CH2
Aliphatic
C-H Stretch
04/22/12
C10H22
CH3(CH2)8CH3
CAS 124-18-5
106
InfraredSpectroscopy
Step17.Halogens
TheHalogensasCH2Xabsorptionsshowupintheregion
(10001300cm1).
UsingIRtoidentifyHalogensinthisregioncanbedifficult,
especiallyifOOPBendingabsorptions(usedforSubstitution
Patterninformation)fromAlkeneandAromaticunsaturated
Pi()bondstructuresarepresent.
HalogenidentificationshouldberestrictedtoAliphaticAlkane
structurescontainingmainlyCH2&CH3groups.
04/22/12
Halogens(Cl,Br,I)showintheFingerprintregion(485800
cm1)asoneortwoabsorptionsseenextslide.
IodideandBromideabsorptionsintherange485650cm1
aregenerallyoutrangeonNaCLSaltPlates,however,if
othersubstrates,e.g.,KBrpellets,areused,theabsorptions
areextendedtothisrange.
107
InfraredSpectroscopy
Step17.Halogens(Cont)
Fluoride
cm1
1000 1400
1000 1200cm1
Polyfluorides
1100 1300cm1
Monofluorides
ArylFluorides
1100 1250cm1
Chloride
540
(2ormorebands)
785cm1
04/22/12
CH2CL(BendWagging)
tButylGroup525cm 1
Bromine
1230 1300cm1
(KBrPellets) 510
650cm1
108
InfraredSpectroscopy
IR Spectrum
Halogens
2-Bromobutane
Br
-C-H
Satn
04/22/12
C4H9Br
CH3
CH2
CH2-Br
CAS 78-76-2
109
InfraredSpectroscopy
IR Spectrum
Halogens
1-Chloropropane
CH3
CH2
CH2-Cl
-C-H
Satn
C3H7Cl
04/22/12
Cl
CAS 540-54-5
110
InfraredSpectroscopy
IR Spectrum
Halogens
o-Chlorotoluene
=C-H
Unsatn
-C-H
Satn
Aromatic
Overtones
O-Disubstitution
CH3
{
Cl
-C=CAromatic
04/22/12
C7H7Cl
CH2-Cl
OOP
o-disubstitution
(750 cm-1)
(missing)
CAS 95-49-8
111
InfraredSpectroscopy
IR Spectrum
Halogens
T-Pentyl Chloride
(2-Chloro-2-MethylButane
Saturated
Aliphatic
C-H Stretch
04/22/12
C5H14CL
CH3
CH2
CH2-Cl
T-Pentyl
525 cm-1
CAS 594-36-5
112
IRAnalysisScheme
Carbonyl (C=O) @ 1715-1685
(Conjugation moves absorption to right ~30 cm-1
Yes
No
Acid
Alcohol
Amine
Ether
Ester
Amide
Anhydride
Aldehyde
Ketone
Saturation
< 3000 cm-1
Unsaturation
> 3000 cm-1
Alkanes
-C-H
Methylene -CH2
Methyl
-CH3
Alkenes (Vinyl)
-C=C
Alkynes (Acetylenes) -CC
Aromatic
-C=C
Nitriles
04/22/12
Hydrocarbons
Nitro
113
IRAnalysisScheme
Carbonyl (C=O) is Present
Acid
- Broad OH Absorption @ 3300-2500 cm-1
Ester
- C-O Absorption @ 1300-1000 cm-1
Amide
- NH Absorption @ 3500 cm-1 (1 or 2 peaks)
Anhydride - 2 C=O Absorptions 1810 & 1760 cm-1
Aldehyde - Aldehyde C-H Absorptions @ 2850 & 2750 cm-1
Ketone
- None of the above except C=O
Carbonyl is Absent
Alcohol - Broad OH absorption @ 3300 - 3000 cm-1
Also C-O absorption @ 1300 - 1000 cm-1
Amine
Ether
04/22/12
- 1 to 2 equal NH absorptions @ 3500 cm-1
- C-O absorption @ 1300 - 1000 cm-1
114
IRAnalysisScheme
Saturation
Alkanes
-C-H Stretch several absorptions to right of 3000 cm-1
Methylene -CH2 1450 cm-1
Methyl
-CH3 1375 cm-1
Unsaturation
Double Bonds
Alkenes (Vinyl)
Alkynes
Alkynes (Acetylenes)
Aromatic (Benzene)
04/22/12
=C-H
Stretch several absorptions to left of 3000 cm-1
OOP bending at 1000 650 cm-1
-C=C- Stretch (weak) @ 1675 1600 cm-1
Conjugation moves absorption to the right
-CC-H Terminal Acetylene Stretch at 3300 cm-1
-CC Stretch @ 2150 cm-1
Conjugation moves absorption to the right
=C-H Stretch absorptions also to left of 3000 cm-1
OOP bending at 900 690 cm-1
OOP absorption patterns allow determination of
ring substitution (p. 897 Pavia text)
-C=C 4 Sharp absorptions (2 pairs) @ 1600 & 1450 cm-1
Overtone absorptions @ 2000 1667 cm-1
Relative shapes and numbers of peaks permit
determination of ring substitution pattern (p. 897 Pavia text).
115