dr. wolf's chm 201 & 202 13- 1 chapter 13 spectroscopy infrared spectroscopy...
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Dr. Wolf's CHM 201 & 202 13- 1
Chapter 13Chapter 13
SpectroscopySpectroscopy
Chapter 13Chapter 13
SpectroscopySpectroscopy
Infrared spectroscopyInfrared spectroscopy
Ultraviolet-Visible spectroscopyUltraviolet-Visible spectroscopy
Nuclear magnetic resonance spectroscopyNuclear magnetic resonance spectroscopy
Mass SpectrometryMass Spectrometry
Dr. Wolf's CHM 201 & 202 13- 2
Principles of Molecular Principles of Molecular
Spectroscopy:Spectroscopy:
Electromagnetic RadiationElectromagnetic Radiation
Principles of Molecular Principles of Molecular
Spectroscopy:Spectroscopy:
Electromagnetic RadiationElectromagnetic Radiation
Dr. Wolf's CHM 201 & 202 13- 3
is propagated at the speed of lightis propagated at the speed of light
has properties of particles and waveshas properties of particles and waves
the energy of a photon is proportional the energy of a photon is proportional to its frequencyto its frequency
Electromagnetic RadiationElectromagnetic RadiationElectromagnetic RadiationElectromagnetic Radiation
Dr. Wolf's CHM 201 & 202 13- 4
Figure 13.1: The Electromagnetic SpectrumFigure 13.1: The Electromagnetic SpectrumFigure 13.1: The Electromagnetic SpectrumFigure 13.1: The Electromagnetic Spectrum
400 nm 750 nm
Visible Light
Longer Wavelength ()Shorter Wavelength ()
Higher Frequency () Lower Frequency ()
Higher Energy (E) Lower Energy (E)
Dr. Wolf's CHM 201 & 202 13- 5
Figure 13.1: The Electromagnetic SpectrumFigure 13.1: The Electromagnetic SpectrumFigure 13.1: The Electromagnetic SpectrumFigure 13.1: The Electromagnetic Spectrum
UltravioletUltraviolet InfraredInfrared
Longer Wavelength (Longer Wavelength ())Shorter Wavelength (Shorter Wavelength ())
Higher Frequency (Higher Frequency ()) Lower Frequency (Lower Frequency ())
Higher Energy (E)Higher Energy (E) Lower Energy (E)Lower Energy (E)
Dr. Wolf's CHM 201 & 202 13- 6
Cosmic rays
Rays
X-rays
Ultraviolet light
Visible light
Infrared radiation
Microwaves
Radio waves
Cosmic rays
Rays
X-rays
Ultraviolet light
Visible light
Infrared radiation
Microwaves
Radio waves
Figure 13.1: The Electromagnetic SpectrumFigure 13.1: The Electromagnetic SpectrumFigure 13.1: The Electromagnetic SpectrumFigure 13.1: The Electromagnetic Spectrum
Energy
Dr. Wolf's CHM 201 & 202 13- 7
Principles of Molecular Spectroscopy: Principles of Molecular Spectroscopy: Quantized Energy StatesQuantized Energy States
Principles of Molecular Spectroscopy: Principles of Molecular Spectroscopy: Quantized Energy StatesQuantized Energy States
Dr. Wolf's CHM 201 & 202 13- 8
Electromagnetic radiation is absorbed when theElectromagnetic radiation is absorbed when the
energy of photon corresponds to difference in energy of photon corresponds to difference in
energy between two states.energy between two states.
E = hE = hE = hE = h
Dr. Wolf's CHM 201 & 202 13- 9
electronicelectronic
vibrationalvibrational
rotationalrotational
nuclear spinnuclear spin
UV-VisUV-Vis
infraredinfrared
microwavemicrowave
radiofrequencyradiofrequency
What Kind of States?What Kind of States?What Kind of States?What Kind of States?
Dr. Wolf's CHM 201 & 202 13- 10
Infrared SpectroscopyInfrared SpectroscopyInfrared SpectroscopyInfrared Spectroscopy
Gives information about the functional groups Gives information about the functional groups in a moleculein a molecule
Dr. Wolf's CHM 201 & 202 13- 11
region of infrared that is most useful lies betweenregion of infrared that is most useful lies between2.5-16 2.5-16 m (4000-625 cmm (4000-625 cm-1-1))
depends on transitions between vibrational depends on transitions between vibrational energy statesenergy states
stretchingstretching
bendingbending
Infrared SpectroscopyInfrared SpectroscopyInfrared SpectroscopyInfrared Spectroscopy
Dr. Wolf's CHM 201 & 202 13- 12
Stretching Vibrations of a CHStretching Vibrations of a CH22 Group GroupStretching Vibrations of a CHStretching Vibrations of a CH22 Group Group
SymmetricSymmetric AntisymmetricAntisymmetric
Dr. Wolf's CHM 201 & 202 13- 13
Bending Vibrations of a CHBending Vibrations of a CH22 Group GroupBending Vibrations of a CHBending Vibrations of a CH22 Group Group
In planeIn plane In planeIn plane
Dr. Wolf's CHM 201 & 202 13- 14
Bending Vibrations of a CHBending Vibrations of a CH22 Group GroupBending Vibrations of a CHBending Vibrations of a CH22 Group Group
Out of planeOut of plane Out of planeOut of plane
Dr. Wolf's CHM 201 & 202 13- 15Francis A. Carey, Organic Chemistry, Fifth Edition. Copyright © 2003 The McGraw-Hill Companies, Inc. All rights reserved.
2000200035003500 30003000 25002500 1000100015001500 500500
Wave number, cmWave number, cm-1-1
Figure 13.31: Infrared Spectrum of HexaneFigure 13.31: Infrared Spectrum of HexaneFigure 13.31: Infrared Spectrum of HexaneFigure 13.31: Infrared Spectrum of Hexane
CHCH33CHCH22CHCH22CHCH22CHCH22CHCH33
C—H stretching
bending bending
bending
Dr. Wolf's CHM 201 & 202 13- 16
2000200035003500 30003000 25002500 1000100015001500 500500
Wave number, cmWave number, cm-1-1
Figure 13.32: Infrared Spectrum of 1-HexeneFigure 13.32: Infrared Spectrum of 1-HexeneFigure 13.32: Infrared Spectrum of 1-HexeneFigure 13.32: Infrared Spectrum of 1-Hexene
HH22C=CHCHC=CHCH22CHCH22CHCH22CHCH33
H—CH—CC=C—HC=C—H
C=CC=C
HH22C=CC=C
Francis A. Carey, Organic Chemistry, Fifth Edition. Copyright © 2003 The McGraw-Hill Companies, Inc. All rights reserved.
Dr. Wolf's CHM 201 & 202 13- 17
Structural unitStructural unit Frequency, cmFrequency, cm-1-1
Stretching vibrations (single bonds)Stretching vibrations (single bonds)
spsp C—H C—H 3310-33203310-3320
spsp22 C—H C—H 3000-31003000-3100
spsp33 C—H C—H 2850-29502850-2950
spsp22 C—O C—O 12001200
spsp33 C—O C—O 1025-12001025-1200
Infrared Absorption FrequenciesInfrared Absorption FrequenciesInfrared Absorption FrequenciesInfrared Absorption Frequencies
Dr. Wolf's CHM 201 & 202 13- 18
Structural unitStructural unit Frequency, cmFrequency, cm-1-1
Stretching vibrations (multiple bonds)Stretching vibrations (multiple bonds)
Infrared Absorption FrequenciesInfrared Absorption FrequenciesInfrared Absorption FrequenciesInfrared Absorption Frequencies
CC CC 1620-16801620-1680
——CC NN
——CC C—C— 2100-22002100-2200
2240-22802240-2280
Dr. Wolf's CHM 201 & 202 13- 19
Structural unitStructural unit Frequency, cmFrequency, cm-1-1
Stretching vibrations (carbonyl groups)Stretching vibrations (carbonyl groups)
Aldehydes and ketonesAldehydes and ketones 1710-17501710-1750
Carboxylic acidsCarboxylic acids 1700-17251700-1725
Acid anhydridesAcid anhydrides 1800-1850 and 1740-17901800-1850 and 1740-1790
EstersEsters 1730-17501730-1750
AmidesAmides 1680-17001680-1700
Infrared Absorption FrequenciesInfrared Absorption FrequenciesInfrared Absorption FrequenciesInfrared Absorption Frequencies
CC OO
Dr. Wolf's CHM 201 & 202 13- 20
Structural unitStructural unit Frequency, cmFrequency, cm-1-1
Bending vibrations of alkenesBending vibrations of alkenes
Infrared Absorption FrequenciesInfrared Absorption FrequenciesInfrared Absorption FrequenciesInfrared Absorption Frequencies
CHCH22RCHRCH
CHCH22RR22CC
CHR'CHR'ciscis-RCH-RCH
CHR'CHR'transtrans-RCH-RCH
CHR'CHR'RR22CC
910-990910-990
890890
665-730665-730
960-980960-980
790-840790-840
Dr. Wolf's CHM 201 & 202 13- 21
Structural unitStructural unit Frequency, cmFrequency, cm-1-1
Bending vibrations of derivatives of benzeneBending vibrations of derivatives of benzene
MonosubstitutedMonosubstituted 730-770 and 690-710730-770 and 690-710
Ortho-disubstitutedOrtho-disubstituted 735-770735-770
Meta-disubstitutedMeta-disubstituted 750-810 and 680-730750-810 and 680-730
Para-disubstitutedPara-disubstituted 790-840790-840
Infrared Absorption FrequenciesInfrared Absorption FrequenciesInfrared Absorption FrequenciesInfrared Absorption Frequencies
Dr. Wolf's CHM 201 & 202 13- 22
2000200035003500 30003000 25002500 1000100015001500 500500
Wave number, cmWave number, cm-1-1
Figure 13.33: Infrared Spectrum of Figure 13.33: Infrared Spectrum of terttert-butylbenzene-butylbenzeneFigure 13.33: Infrared Spectrum of Figure 13.33: Infrared Spectrum of terttert-butylbenzene-butylbenzene
H—CH—C
Ar—HAr—H
MonsubstitutedMonsubstitutedbenzenebenzene
CC66HH55C(CHC(CH33))33
Francis A. Carey, Organic Chemistry, Fifth Edition. Copyright © 2003 The McGraw-Hill Companies, Inc. All rights reserved.
Dr. Wolf's CHM 201 & 202 13- 23
Structural unitStructural unit Frequency, Frequency, cmcm-1-1
Stretching vibrations (single bonds)Stretching vibrations (single bonds)
O—H (alcohols)O—H (alcohols) 3200-36003200-3600
O—H (carboxylic acids) O—H (carboxylic acids) 3000-31003000-3100
N—HN—H 3350-35003350-3500
Infrared Absorption FrequenciesInfrared Absorption FrequenciesInfrared Absorption FrequenciesInfrared Absorption Frequencies
Dr. Wolf's CHM 201 & 202 13- 24
2000200035003500 30003000 25002500 1000100015001500 500500
Wave number, cmWave number, cm-1-1
Figure 13.34: Infrared Spectrum of 2-HexanolFigure 13.34: Infrared Spectrum of 2-HexanolFigure 13.34: Infrared Spectrum of 2-HexanolFigure 13.34: Infrared Spectrum of 2-Hexanol
H—CH—C
O—HO—H
OHOH
CHCH33CHCH22CHCH22CHCH22CHCHCHCH33
Francis A. Carey, Organic Chemistry, Fifth Edition. Copyright © 2003 The McGraw-Hill Companies, Inc. All rights reserved.
Dr. Wolf's CHM 201 & 202 13- 25
2000200035003500 30003000 25002500 1000100015001500 500500
Wave number, cmWave number, cm-1-1
Figure 13.35: Infrared Spectrum of 2-HexanoneFigure 13.35: Infrared Spectrum of 2-HexanoneFigure 13.35: Infrared Spectrum of 2-HexanoneFigure 13.35: Infrared Spectrum of 2-Hexanone
H—CH—C
C=OC=O
OO
CHCH33CHCH22CHCH22CHCH22CCHCCH33
Francis A. Carey, Organic Chemistry, Fifth Edition. Copyright © 2003 The McGraw-Hill Companies, Inc. All rights reserved.
Dr. Wolf's CHM 201 & 202 13- 26
Ultraviolet-Visible (UV-VIS) Ultraviolet-Visible (UV-VIS)
SpectroscopySpectroscopy
Ultraviolet-Visible (UV-VIS) Ultraviolet-Visible (UV-VIS)
SpectroscopySpectroscopy
Gives information about conjugated Gives information about conjugated electron electron systemssystems
Dr. Wolf's CHM 201 & 202 13- 27
gaps between electron energy gaps between electron energy levels are greater than thoselevels are greater than thosebetween vibrational levelsbetween vibrational levels
gap corresponds to wavelengthsgap corresponds to wavelengthsbetween 200 and 800 nmbetween 200 and 800 nm
Transitions between electron energy statesTransitions between electron energy statesTransitions between electron energy statesTransitions between electron energy states
EE = = hh
Dr. Wolf's CHM 201 & 202 13- 28
X-axis is wavelength in nm (high energy at left, X-axis is wavelength in nm (high energy at left, low energy at right)low energy at right)
maxmax is the wavelength of maximum absorption is the wavelength of maximum absorption
and is related to electronic makeup of molecule— and is related to electronic makeup of molecule— especially especially electron system electron system
Y axis is a measure of absorption of electromagnetic Y axis is a measure of absorption of electromagnetic radiation expressed as molar absorptivity (radiation expressed as molar absorptivity ())
Conventions in UV-VISConventions in UV-VISConventions in UV-VISConventions in UV-VIS
Dr. Wolf's CHM 201 & 202 13- 29
200200 220220 240240 260260 280280
10001000
20002000
Wavelength, nmWavelength, nm
maxmax 230 nm 230 nm
maxmax 2630 2630
MolarMolar
absorptivity (absorptivity ())
UV Spectrum of cis,trans-1,3-cyclooctadieneUV Spectrum of cis,trans-1,3-cyclooctadieneUV Spectrum of cis,trans-1,3-cyclooctadieneUV Spectrum of cis,trans-1,3-cyclooctadiene
Dr. Wolf's CHM 201 & 202 13- 30
Most stable Most stable -electron -electron
configurationconfiguration
-Electron -Electron configuration of configuration of
excited stateexcited state
* Transition in cis,trans-1,3-cyclooctadiene* Transition in cis,trans-1,3-cyclooctadiene* Transition in cis,trans-1,3-cyclooctadiene* Transition in cis,trans-1,3-cyclooctadiene
HOMOHOMO
LUMOLUMO
EE = = hh
Dr. Wolf's CHM 201 & 202 13- 31
* Transition in Alkenes* Transition in Alkenes* Transition in Alkenes* Transition in Alkenes
HOMO-LUMO energy gap is affected by HOMO-LUMO energy gap is affected by substituents on double bondsubstituents on double bond
as HOMO-LUMO energy difference as HOMO-LUMO energy difference decreases (smaller decreases (smaller EE), ), maxmax shifts to longer shifts to longer
wavelengthswavelengths
Dr. Wolf's CHM 201 & 202 13- 32
Methyl groups on double bond cause Methyl groups on double bond cause maxmax
to shift to longer wavelengthsto shift to longer wavelengths
CC CC
HH
HH
HH
HH
CC CC
HH
HH CHCH33
maxmax 170 nm 170 nm
CHCH33
maxmax 188 nm 188 nm
Dr. Wolf's CHM 201 & 202 13- 33
Extending conjugation has a larger effect Extending conjugation has a larger effect on on maxmax; shift is again to longer ; shift is again to longer
wavelengthswavelengths
CC CC
HH
HH
HH
HH
CC CC
HH
HH
maxmax 170 nm 170 nmmaxmax 217 nm 217 nm
HH
CC CC
HH
HHHH
Dr. Wolf's CHM 201 & 202 13- 34
maxmax 217 nm 217 nm
(conjugated (conjugated dienediene))
HH
CC CC
HH
HH CC CC
HH
HHHH
CC CC
HH CHCH33
HH
HH
CC CC
HH33CC
HH CC CC
HH
HH
maxmax 263 nm 263 nm
conjugated conjugated trienetriene plus plus two methyl groupstwo methyl groups
Dr. Wolf's CHM 201 & 202 13- 35
LycopeneLycopeneLycopeneLycopene
maxmax 505 nm 505 nm
orange-red pigment in tomatoesorange-red pigment in tomatoes
Dr. Wolf's CHM 201 & 202 13- 36
Mass SpectrometryMass SpectrometryMass SpectrometryMass Spectrometry
Dr. Wolf's CHM 201 & 202 13- 37
Atom or molecule is hit by high-energy electronAtom or molecule is hit by high-energy electron
Principles of Electron-Impact Mass SpectrometryPrinciples of Electron-Impact Mass SpectrometryPrinciples of Electron-Impact Mass SpectrometryPrinciples of Electron-Impact Mass Spectrometry
ee––
Dr. Wolf's CHM 201 & 202 13- 38
Atom or molecule is hit by high-energy electronAtom or molecule is hit by high-energy electron
electron is deflected but transfers much of its electron is deflected but transfers much of its energy to the moleculeenergy to the molecule
ee––
Principles of Electron-Impact Mass SpectrometryPrinciples of Electron-Impact Mass SpectrometryPrinciples of Electron-Impact Mass SpectrometryPrinciples of Electron-Impact Mass Spectrometry
Dr. Wolf's CHM 201 & 202 13- 39
Atom or molecule is hit by high-energy electronAtom or molecule is hit by high-energy electron
electron is deflected but transfers much of its electron is deflected but transfers much of its energy to the moleculeenergy to the molecule
ee––
Principles of Electron-Impact Mass SpectrometryPrinciples of Electron-Impact Mass SpectrometryPrinciples of Electron-Impact Mass SpectrometryPrinciples of Electron-Impact Mass Spectrometry
Dr. Wolf's CHM 201 & 202 13- 40
This energy-rich species ejects an electron.This energy-rich species ejects an electron.
Principles of Electron-Impact Mass SpectrometryPrinciples of Electron-Impact Mass SpectrometryPrinciples of Electron-Impact Mass SpectrometryPrinciples of Electron-Impact Mass Spectrometry
Dr. Wolf's CHM 201 & 202 13- 41
This energy-rich species ejects an electron.This energy-rich species ejects an electron.
Principles of Electron-Impact Mass SpectrometryPrinciples of Electron-Impact Mass SpectrometryPrinciples of Electron-Impact Mass SpectrometryPrinciples of Electron-Impact Mass Spectrometry
forming a positively charged, odd-electron species forming a positively charged, odd-electron species called the called the molecular ionmolecular ion
ee––++••
Dr. Wolf's CHM 201 & 202 13- 42
Molecular ion passes between poles of a Molecular ion passes between poles of a magnet and is deflected by magnetic fieldmagnet and is deflected by magnetic field
amount of amount of deflection depends deflection depends on mass-to-charge on mass-to-charge ratioratio
highest m/z highest m/z deflected leastdeflected least
lowest m/z lowest m/z deflected mostdeflected most
Principles of Electron-Impact Mass SpectrometryPrinciples of Electron-Impact Mass SpectrometryPrinciples of Electron-Impact Mass SpectrometryPrinciples of Electron-Impact Mass Spectrometry
++••
Dr. Wolf's CHM 201 & 202 13- 43
Principles of Electron-Impact Mass SpectrometryPrinciples of Electron-Impact Mass SpectrometryPrinciples of Electron-Impact Mass SpectrometryPrinciples of Electron-Impact Mass Spectrometry
If the only ion that is present is the molecular ion, If the only ion that is present is the molecular ion, mass spectrometry provides a way to measure the mass spectrometry provides a way to measure the molecular weight of a compound and is often used for molecular weight of a compound and is often used for this purpose.this purpose.
However, the molecular ion often fragments to a However, the molecular ion often fragments to a mixture of species of lower m/z.mixture of species of lower m/z.
Dr. Wolf's CHM 201 & 202 13- 44
The molecular ion dissociates to a cationThe molecular ion dissociates to a cationand a radical.and a radical.
Principles of Electron-Impact Mass SpectrometryPrinciples of Electron-Impact Mass SpectrometryPrinciples of Electron-Impact Mass SpectrometryPrinciples of Electron-Impact Mass Spectrometry
++••
Dr. Wolf's CHM 201 & 202 13- 45
The molecular ion dissociates to a cationThe molecular ion dissociates to a cationand a radical.and a radical.
Principles of Electron-Impact Mass SpectrometryPrinciples of Electron-Impact Mass SpectrometryPrinciples of Electron-Impact Mass SpectrometryPrinciples of Electron-Impact Mass Spectrometry
++ ••
Usually several fragmentation pathways are available Usually several fragmentation pathways are available and a mixture of ions is produced.and a mixture of ions is produced.
Dr. Wolf's CHM 201 & 202 13- 46
mixture of ions of mixture of ions of different mass different mass gives separate peak gives separate peak for each m/zfor each m/z
intensity of peak intensity of peak proportional to proportional to percentage of each percentage of each ion of different ion of different mass in mixturemass in mixture
separation of peaks separation of peaks depends on relative depends on relative massmass
Principles of Electron-Impact Mass SpectrometryPrinciples of Electron-Impact Mass SpectrometryPrinciples of Electron-Impact Mass SpectrometryPrinciples of Electron-Impact Mass Spectrometry
++
++++
++
+
+
Dr. Wolf's CHM 201 & 202 13- 47
mixture of ions of mixture of ions of different mass different mass gives separate peak gives separate peak for each m/zfor each m/z
intensity of peak intensity of peak proportional to proportional to percentage of each percentage of each atom of different atom of different mass in mixturemass in mixture
separation of peaks separation of peaks depends on relative depends on relative massmass
++ ++ ++ ++
+ +
Principles of Electron-Impact Mass SpectrometryPrinciples of Electron-Impact Mass SpectrometryPrinciples of Electron-Impact Mass SpectrometryPrinciples of Electron-Impact Mass Spectrometry
Dr. Wolf's CHM 201 & 202 13- 48
2020 4040 6060 8080 100100 120 120
m/zm/z
m/z m/z = 78= 78
100100
8080
6060
4040
2020
00
Relative Relative intensityintensity
Some molecules undergo very little Some molecules undergo very little fragmentationfragmentation
Some molecules undergo very little Some molecules undergo very little fragmentationfragmentation
Benzene is an example. The major peak Benzene is an example. The major peak corresponds to the molecular ion.corresponds to the molecular ion.
Dr. Wolf's CHM 201 & 202 13- 49
HH
HH HH
HHHH
HH
HH
HH HH
HHHH
HH
HH
HH HH
HHHH
HH
all H are all H are 11H and all H and all C are C are 1212CC
one C is one C is 1313CC one H is one H is 22HH
Isotopic ClustersIsotopic ClustersIsotopic ClustersIsotopic Clusters
7878 7979 7979
93.4%93.4% 6.5%6.5% 0.1%0.1%
Dr. Wolf's CHM 201 & 202 13- 50
2020 4040 6060 8080 100100 120 120
m/zm/z
100100
8080
6060
4040
2020
00
Relative Relative intensityintensity
112112
114114
Isotopic ClustersIsotopic Clustersin Chlorobenzenein Chlorobenzene
Isotopic ClustersIsotopic Clustersin Chlorobenzenein Chlorobenzene
visible in peaks for visible in peaks for molecular ionmolecular ion
3535ClCl 3737ClCl
Dr. Wolf's CHM 201 & 202 13- 51
2020 4040 6060 8080 100100 120 120
m/zm/z
Relative Relative intensityintensity
7777
Isotopic ClustersIsotopic Clustersin Chlorobenzenein Chlorobenzene
Isotopic ClustersIsotopic Clustersin Chlorobenzenein Chlorobenzene
no no mm//zz 77, 79 pair; 77, 79 pair; therefore ion therefore ion responsible forresponsible formm//zz 77 peak does 77 peak does not contain Clnot contain Cl
HH
HH
HH
HH
HH ++
100100
8080
6060
4040
2020
00
Dr. Wolf's CHM 201 & 202 13- 52
Alkanes undergo extensive fragmentationAlkanes undergo extensive fragmentationAlkanes undergo extensive fragmentationAlkanes undergo extensive fragmentation
m/zm/z
DecaneDecane
142142
4343
5757
7171
8585
9999
CHCH33—CH—CH22—CH—CH22—CH—CH22—CH—CH22—CH—CH22—CH—CH22—CH—CH22—CH—CH22—CH—CH33
Relative Relative intensityintensity
100100
8080
6060
4040
2020
00
2020 4040 6060 8080 100100 120 120
Dr. Wolf's CHM 201 & 202 13- 53
Propylbenzene fragments mostlyPropylbenzene fragments mostlyat the benzylic positionat the benzylic position
Propylbenzene fragments mostlyPropylbenzene fragments mostlyat the benzylic positionat the benzylic position
2020 4040 6060 8080 100100 120 120
m/zm/z
Relative Relative intensityintensity
120120
9191 CHCH22—CH—CH22CHCH33
100100
8080
6060
4040
2020
00
Dr. Wolf's CHM 201 & 202 13- 54
Molecular FormulaMolecular Formula
as aas a
Clue to StructureClue to Structure
Molecular FormulaMolecular Formula
as aas a
Clue to StructureClue to Structure
Dr. Wolf's CHM 201 & 202 13- 55
Molecular WeightsMolecular WeightsMolecular WeightsMolecular Weights
One of the first pieces of information we try to One of the first pieces of information we try to obtain when determining a molecular obtain when determining a molecular structure is the molecular formula.structure is the molecular formula.
However, we can gain some information even However, we can gain some information even from the molecular weight. Mass from the molecular weight. Mass spectrometry makes it relatively easy to spectrometry makes it relatively easy to determine molecular weights.determine molecular weights.
Dr. Wolf's CHM 201 & 202 13- 56
The Nitrogen RuleThe Nitrogen RuleThe Nitrogen RuleThe Nitrogen Rule
A molecule with an A molecule with an odd number of odd number of nitrogens has an odd nitrogens has an odd molecular weight.molecular weight.
A molecule that A molecule that contains only C, H, contains only C, H, and O or which has and O or which has an even number of an even number of nitrogens has an nitrogens has an even molecular even molecular weight.weight.
NNHH22 9393
138138
NNHH22OO22NN
183183
NNHH22OO22NN
NNOO22
Dr. Wolf's CHM 201 & 202 13- 57
Exact Molecular WeightsExact Molecular WeightsExact Molecular WeightsExact Molecular Weights
CHCH33(CH(CH22))55CHCH33
HeptaneHeptane
CHCH33COCO
OO Cyclopropyl acetateCyclopropyl acetate
Molecular formulaMolecular formula
Molecular weightMolecular weight
CC77HH1616 CC55HH88OO22
100100 100100
Exact massExact mass 100.1253100.1253 100.0524100.0524
Mass spectrometry can measure exact Mass spectrometry can measure exact masses. Therefore, mass spectrometry can masses. Therefore, mass spectrometry can give molecular formulas.give molecular formulas.
Dr. Wolf's CHM 201 & 202 13- 58
Molecular FormulasMolecular FormulasMolecular FormulasMolecular Formulas
Knowing that the molecular formula of a Knowing that the molecular formula of a substance is Csubstance is C77HH1616 tells us immediately that is tells us immediately that is
an alkane because it corresponds to Can alkane because it corresponds to CnnHH22nn+2+2
CC77HH1414 lacks two hydrogens of an alkane, lacks two hydrogens of an alkane,
therefore contains either a ring or a double therefore contains either a ring or a double bond bond
Dr. Wolf's CHM 201 & 202 13- 59
Index of Hydrogen DeficiencyIndex of Hydrogen DeficiencyIndex of Hydrogen DeficiencyIndex of Hydrogen Deficiency
relates molecular formulas to multiple bonds relates molecular formulas to multiple bonds and ringsand rings
index of hydrogen deficiency = index of hydrogen deficiency =
1122
(molecular formula of alkane –(molecular formula of alkane – molecular formula of compound) molecular formula of compound)
Dr. Wolf's CHM 201 & 202 13- 60
Example 1Example 1Example 1Example 1
index of hydrogen deficiency index of hydrogen deficiency
C7H14C7H14
1122
(molecular formula of alkane –(molecular formula of alkane – molecular formula of compound) molecular formula of compound)
==
1122
(C(C77HH1616 – C – C77HH1414))==
1122
(2) = 1(2) = 1==
Therefore, one ring or one double bond.Therefore, one ring or one double bond.
Dr. Wolf's CHM 201 & 202 13- 61
Example 2Example 2Example 2Example 2
C7H12C7H12
1122
(C(C77HH1616 – C – C77HH1212))==
1122
(4) = 2(4) = 2==
Therefore, two rings, one triple bond,Therefore, two rings, one triple bond,two double bonds, or one double bond + one ring.two double bonds, or one double bond + one ring.
Dr. Wolf's CHM 201 & 202 13- 62
Oxygen has no effectOxygen has no effectOxygen has no effectOxygen has no effect
CHCH33(CH(CH22))55CHCH22OH (1-heptanol, COH (1-heptanol, C77HH1616O) has O) has
same number of H atoms as heptanesame number of H atoms as heptane
index of hydrogen deficiency = index of hydrogen deficiency =
1122
(C(C77HH1616 – C – C77HH1616O)O) = 0= 0
no rings or double bondsno rings or double bonds
Dr. Wolf's CHM 201 & 202 13- 63
Oxygen has no effectOxygen has no effectOxygen has no effectOxygen has no effect
index of hydrogen deficiency = index of hydrogen deficiency =
1122
(C(C55HH1212 – C – C55HH88OO22)) = 2= 2
one ring plus one double bondone ring plus one double bond
CHCH33COCO
OO Cyclopropyl acetateCyclopropyl acetate
Dr. Wolf's CHM 201 & 202 13- 64
If halogen is presentIf halogen is presentIf halogen is presentIf halogen is present
Treat a halogen as if it were hydrogen.Treat a halogen as if it were hydrogen.
CC CC
CHCH33
ClClHH
HH
CC33HH55ClCl
same index of hydrogensame index of hydrogendeficiency as for Cdeficiency as for C33HH66
Dr. Wolf's CHM 201 & 202 13- 65
Rings versus Multiple BondsRings versus Multiple BondsRings versus Multiple BondsRings versus Multiple Bonds
Index of hydrogen deficiency tells us the sum ofIndex of hydrogen deficiency tells us the sum ofrings plus multiple bonds.rings plus multiple bonds.
Catalytic hydrogenation tells us how many Catalytic hydrogenation tells us how many multiple bonds there are.multiple bonds there are.
Dr. Wolf's CHM 201 & 202 13- 66
Introduction to Introduction to 11H NMR SpectroscopyH NMR Spectroscopy
Introduction to Introduction to 11H NMR SpectroscopyH NMR Spectroscopy
Dr. Wolf's CHM 201 & 202 13- 67
11H and H and 1313CC
both have spin = ±1/2both have spin = ±1/2
11H is 99% at natural abundanceH is 99% at natural abundance
1313C is 1.1% at natural abundanceC is 1.1% at natural abundance
The nuclei that are most useful toThe nuclei that are most useful to
organic chemists are:organic chemists are:
The nuclei that are most useful toThe nuclei that are most useful to
organic chemists are:organic chemists are:
Dr. Wolf's CHM 201 & 202 13- 68
Nuclear SpinNuclear SpinNuclear SpinNuclear Spin
A spinning charge, such as the nucleus of A spinning charge, such as the nucleus of 11H H or or 1313C, generates a C, generates a magnetic fieldmagnetic field. The . The magnetic fieldmagnetic field generated by a nucleus of spin generated by a nucleus of spin +1/2 is opposite in direction from that +1/2 is opposite in direction from that generated by a nucleus of spin –1/2.generated by a nucleus of spin –1/2.
+ +
Dr. Wolf's CHM 201 & 202 13- 69
++
+
+
+
The distribution of The distribution of nuclear spins is nuclear spins is random in the random in the absence of an absence of an external magnetic external magnetic field.field.
The distribution of The distribution of nuclear spins is nuclear spins is random in the random in the absence of an absence of an external magnetic external magnetic field.field.
Dr. Wolf's CHM 201 & 202 13- 70
++
+
+
+An external magnetic An external magnetic field causes nuclear field causes nuclear magnetic moments to magnetic moments to align parallel and align parallel and antiparallel to applied antiparallel to applied field.field.
An external magnetic An external magnetic field causes nuclear field causes nuclear magnetic moments to magnetic moments to align parallel and align parallel and antiparallel to applied antiparallel to applied field.field.
HH00
Dr. Wolf's CHM 201 & 202 13- 71
++
+
+
+
There is a slight There is a slight excess of nuclear excess of nuclear magnetic moments magnetic moments aligned parallel to aligned parallel to the applied field.the applied field.
There is a slight There is a slight excess of nuclear excess of nuclear magnetic moments magnetic moments aligned parallel to aligned parallel to the applied field.the applied field.
HH00
Dr. Wolf's CHM 201 & 202 13- 72
no difference in absence of magnetic fieldno difference in absence of magnetic fieldproportional to strength of external magnetic field proportional to strength of external magnetic field
Energy Differences Between Nuclear Spin StatesEnergy Differences Between Nuclear Spin StatesEnergy Differences Between Nuclear Spin StatesEnergy Differences Between Nuclear Spin States
+
+
EE E E ''
increasing field strengthincreasing field strength
Dr. Wolf's CHM 201 & 202 13- 73
Some important relationships in NMRSome important relationships in NMRSome important relationships in NMRSome important relationships in NMR
The frequency of absorbedThe frequency of absorbedelectromagnetic radiationelectromagnetic radiationis proportional tois proportional to
the energy difference betweenthe energy difference betweentwo nuclear spin statestwo nuclear spin stateswhich is proportional towhich is proportional to
the applied magnetic fieldthe applied magnetic field
UnitsUnits
HzHz
kJ/molkJ/mol(kcal/mol)(kcal/mol)
tesla (T)tesla (T)
Dr. Wolf's CHM 201 & 202 13- 74
Some important relationships in NMRSome important relationships in NMRSome important relationships in NMRSome important relationships in NMR
The frequency of absorbed electromagneticThe frequency of absorbed electromagneticradiation is different for different elements, radiation is different for different elements, and for different isotopes of the same element.and for different isotopes of the same element.
For a field strength of 4.7 T:For a field strength of 4.7 T:11H absorbs radiation having a frequencyH absorbs radiation having a frequencyof 200 MHz (200 x 10of 200 MHz (200 x 1066 s s-1-1))1313C absorbs radiation having a frequencyC absorbs radiation having a frequencyof 50.4 MHz (50.4 x 10of 50.4 MHz (50.4 x 1066 s s-1-1))
Dr. Wolf's CHM 201 & 202 13- 75
Some important relationships in NMRSome important relationships in NMRSome important relationships in NMRSome important relationships in NMR
The frequency of absorbed electromagneticThe frequency of absorbed electromagneticradiation for a particular nucleus (such as radiation for a particular nucleus (such as 11H)H)depends on its molecular environment. depends on its molecular environment.
This is why NMR is such a useful toolThis is why NMR is such a useful toolfor structure determination.for structure determination.
Dr. Wolf's CHM 201 & 202 13- 76
Nuclear ShieldingNuclear Shieldingandand
11H Chemical ShiftsH Chemical Shifts
Nuclear ShieldingNuclear Shieldingandand
11H Chemical ShiftsH Chemical Shifts
What do we mean by "shielding?"What do we mean by "shielding?"
What do we mean by "chemical shift?"What do we mean by "chemical shift?"
Dr. Wolf's CHM 201 & 202 13- 77
ShieldingShieldingShieldingShielding
An external magnetic field An external magnetic field affects the motion of the affects the motion of the electrons in a molecule, electrons in a molecule, inducing a magnetic field inducing a magnetic field within the molecule.within the molecule.
The direction of the The direction of the induced magnetic field is induced magnetic field is opposite to that of the opposite to that of the applied field.applied field.
CC HH
HH 00
Dr. Wolf's CHM 201 & 202 13- 78
ShieldingShieldingShieldingShielding
The induced field shields The induced field shields the nuclei (in this case, C the nuclei (in this case, C and H) from the applied and H) from the applied field.field.
A stronger external field is A stronger external field is needed in order for energy needed in order for energy difference between spin difference between spin states to match energy of states to match energy of rf radiation.rf radiation.
CC HH
HH 00
Dr. Wolf's CHM 201 & 202 13- 79
Chemical ShiftChemical ShiftChemical ShiftChemical Shift
Chemical shift is a Chemical shift is a measure of the degree to measure of the degree to which a nucleus in a which a nucleus in a molecule is shielded.molecule is shielded.
Protons in different Protons in different environments are shielded environments are shielded to greater or lesser to greater or lesser degrees; they have degrees; they have different chemical shifts.different chemical shifts.
CC HH
HH 00
Dr. Wolf's CHM 201 & 202 13- 80
Chemical ShiftChemical ShiftChemical ShiftChemical Shift
Chemical shifts (Chemical shifts () are ) are measured relative to the measured relative to the protons in protons in tetramethylsilane (TMS) tetramethylsilane (TMS) as a standard.as a standard.
SiSi CHCH33
CHCH33
CHCH33
HH33CC
==position of signal - position of TMS peakposition of signal - position of TMS peak
spectrometer frequencyspectrometer frequencyx 10x 1066
Dr. Wolf's CHM 201 & 202 13- 81
01.02.03.04.05.06.07.08.09.010.0
Chemical shift (Chemical shift (, ppm), ppm)
measured relative to TMSmeasured relative to TMS
UpfieldUpfieldIncreased shieldingIncreased shielding
DownfieldDownfieldDecreased shieldingDecreased shielding
(CH(CH33))44Si (TMS)Si (TMS)
Dr. Wolf's CHM 201 & 202 13- 82
Chemical ShiftChemical ShiftChemical ShiftChemical Shift
Example: The signal for the proton in chloroform Example: The signal for the proton in chloroform (HCCl(HCCl33) appears 1456 Hz downfield from TMS at a ) appears 1456 Hz downfield from TMS at a
spectrometer frequency of 200 MHz.spectrometer frequency of 200 MHz.
==position of signal - position of TMS peakposition of signal - position of TMS peak
spectrometer frequencyspectrometer frequencyx 10x 1066
==1456 Hz - 0 Hz1456 Hz - 0 Hz
200 x 10200 x 1066 Hx Hxx 10x 1066
= 7.28= 7.28
Dr. Wolf's CHM 201 & 202 13- 83
01.02.03.04.05.06.07.08.09.010.0
Chemical shift (Chemical shift (, ppm), ppm)
7.28 ppm7.28 ppm
HH CC
ClCl
ClCl
ClCl
Dr. Wolf's CHM 201 & 202 13- 84
Effects of Molecular StructureEffects of Molecular Structureonon
11H Chemical ShiftsH Chemical Shifts
Effects of Molecular StructureEffects of Molecular Structureonon
11H Chemical ShiftsH Chemical Shifts
protons in different environments experience protons in different environments experience different degrees of shielding and have different degrees of shielding and have
different chemical shiftsdifferent chemical shifts
Dr. Wolf's CHM 201 & 202 13- 85
Electronegative substituents decreaseElectronegative substituents decrease
the shielding of methyl groupsthe shielding of methyl groups
Electronegative substituents decreaseElectronegative substituents decrease
the shielding of methyl groupsthe shielding of methyl groups
least shielded H most shielded H CH3F CH3OCH3 (CH3)3N CH3CH3 (CH3)4Si
4.3 3.2 2.2 0.9 0.0
Dr. Wolf's CHM 201 & 202 13- 86
Electronegative substituents decrease shieldingElectronegative substituents decrease shieldingElectronegative substituents decrease shieldingElectronegative substituents decrease shielding
HH33C—CC—CHH22—C—CHH33
OO22N—CN—CHH22—C—CHH22—C—CHH33
0.90.9 0.90.9 1.31.3
1.01.0 4.34.3 2.02.0
Dr. Wolf's CHM 201 & 202 13- 87
Effect is cumulativeEffect is cumulativeEffect is cumulativeEffect is cumulative
CHCHClCl33 7.3 7.3
CHCH22ClCl22 5.3 5.3
CHCH33ClCl 3.1 3.1
Dr. Wolf's CHM 201 & 202 13- 88
Methyl, Methylene, and MethineMethyl, Methylene, and MethineMethyl, Methylene, and MethineMethyl, Methylene, and Methine
CCHH33 more shielded than CH more shielded than CH2 2 ; ; CCHH22
more shielded than Cmore shielded than CHH
HH33CC CC
CCHH33
CHCH33
HH
0.90.9
1.61.6
0.80.8
HH33CC CC
CCHH33
CHCH33
CCHH22
0.90.9
CHCH33
1.21.2
Dr. Wolf's CHM 201 & 202 13- 89
Protons attached to spProtons attached to sp22 hybridized carbon hybridized carbonare less shielded than those attachedare less shielded than those attached
to spto sp33 hybridized carbon hybridized carbon
Protons attached to spProtons attached to sp22 hybridized carbon hybridized carbonare less shielded than those attachedare less shielded than those attached
to spto sp33 hybridized carbon hybridized carbon HH HH
HHHH
HH
HH
CC CC
HHHH
HH HH
CHCH33CHCH33
7.37.3 5.35.3 0.90.9
Dr. Wolf's CHM 201 & 202 13- 90
But protons attached to sp hybridized carbonBut protons attached to sp hybridized carbonare more shielded than those attachedare more shielded than those attached
to spto sp22 hybridized carbon hybridized carbon
But protons attached to sp hybridized carbonBut protons attached to sp hybridized carbonare more shielded than those attachedare more shielded than those attached
to spto sp22 hybridized carbon hybridized carbon
CC CC
HHHH
HH HH
5.35.3
2.42.4CHCH22OCHOCH33CC CCHH
Dr. Wolf's CHM 201 & 202 13- 91
Protons attached to benzylic and allylicProtons attached to benzylic and allyliccarbons are somewhat less shielded than usualcarbons are somewhat less shielded than usual
Protons attached to benzylic and allylicProtons attached to benzylic and allyliccarbons are somewhat less shielded than usualcarbons are somewhat less shielded than usual
1.51.5 0.80.8
HH33CC CHCH33
1.21.2
HH33CC CHCH22
2.62.6
HH33C—CHC—CH22—CH—CH33
0.90.9 0.90.9 1.31.3
Dr. Wolf's CHM 201 & 202 13- 92
Proton attached to C=O of aldehydeProton attached to C=O of aldehydeis most deshielded C—His most deshielded C—H
Proton attached to C=O of aldehydeProton attached to C=O of aldehydeis most deshielded C—His most deshielded C—H
2.42.4
9.79.7
1.11.1
CC CC
OO
HH
HH
CHCH33
HH33CC
Dr. Wolf's CHM 201 & 202 13- 93
Type of protonType of proton Chemical shift (Chemical shift (),),ppmppm
Type of protonType of proton Chemical shift (Chemical shift (),),ppmppm
CCHH RR 0.9-1.80.9-1.8
1.5-2.61.5-2.6CCHH CCCC
2.0-2.52.0-2.5CCHH CC
OO
2.1-2.32.1-2.3CCHH NNCC
CCHH ArAr 2.3-2.82.3-2.8
2.52.5CCHH CCCC
Dr. Wolf's CHM 201 & 202 13- 94
Type of protonType of proton Chemical shift (Chemical shift (),),ppmppm
Type of protonType of proton Chemical shift (Chemical shift (),),ppmppm
CCHH BrBr 2.7-4.12.7-4.1
9-109-10CC
OO
HH
2.2-2.92.2-2.9CCHH NRNR
3.1-4.13.1-4.1CCHH ClCl
6.5-8.56.5-8.5HH ArAr
CC CC
HH
4.5-6.54.5-6.5
3.3-3.73.3-3.7CCHH OO
Dr. Wolf's CHM 201 & 202 13- 95
Type of protonType of proton Chemical shift (Chemical shift (),),ppmppm
1-31-3HH NRNR
0.5-50.5-5HH OROR
6-86-8HH OArOAr
10-1310-13CC
OO
HHOO
Dr. Wolf's CHM 201 & 202 13- 96
Interpreting Proton NMR Interpreting Proton NMR
SpectraSpectra
Interpreting Proton NMR Interpreting Proton NMR
SpectraSpectra
Dr. Wolf's CHM 201 & 202 13- 97
1. number of signals1. number of signals
2. their intensity (as measured by area 2. their intensity (as measured by area under peak)under peak)
3. splitting pattern (multiplicity)3. splitting pattern (multiplicity)
Information contained in an NMRInformation contained in an NMRspectrum includes:spectrum includes:
Information contained in an NMRInformation contained in an NMRspectrum includes:spectrum includes:
Dr. Wolf's CHM 201 & 202 13- 98
Number of SignalsNumber of SignalsNumber of SignalsNumber of Signals
protons that have different chemical shifts protons that have different chemical shifts are chemically nonequivalentare chemically nonequivalent
exist in different molecular environmentexist in different molecular environment
Dr. Wolf's CHM 201 & 202 13- 99
01.02.03.04.05.06.07.08.09.010.0
Chemical shift (Chemical shift (, ppm), ppm)
CCCCHH22OCOCHH33NN
OCOCHH33
NCCNCCHH22OO
Dr. Wolf's CHM 201 & 202 13- 100
are in identical environmentsare in identical environments
have same chemical shifthave same chemical shift
replacement test: replacement by some replacement test: replacement by some arbitrary "test group" generates same compoundarbitrary "test group" generates same compound
HH33CCHCCH22CCHH33
chemically equivalentchemically equivalent
Chemically equivalent protonsChemically equivalent protonsChemically equivalent protonsChemically equivalent protons
Dr. Wolf's CHM 201 & 202 13- 101
HH33CCHCCH22CCHH33
chemically equivalentchemically equivalent
CCHH33CHCH22CCHH22ClClClClCCHH22CHCH22CCHH33
Chemically equivalent protonsChemically equivalent protonsChemically equivalent protonsChemically equivalent protons
Replacing protons at C-1 and C-3 gives same Replacing protons at C-1 and C-3 gives same compound (1-chloropropane)compound (1-chloropropane)
C-1 and C-3 protons are chemically C-1 and C-3 protons are chemically equivalent and have the same chemical shiftequivalent and have the same chemical shift
Dr. Wolf's CHM 201 & 202 13- 102
replacement by some arbitrary test group replacement by some arbitrary test group generates diastereomersgenerates diastereomers
diastereotopic protons can have differentdiastereotopic protons can have differentchemical shiftschemical shifts
Diastereotopic protonsDiastereotopic protonsDiastereotopic protonsDiastereotopic protons
CC CC
BrBr
HH33CC
HH
HH
5.3 ppm5.3 ppm
5.5 ppm5.5 ppm
Dr. Wolf's CHM 201 & 202 13- 103
not all peaks are singletsnot all peaks are singlets
signals can be split by coupling of signals can be split by coupling of nuclear spinsnuclear spins
Spin-Spin SplittingSpin-Spin Splittinginin
NMR SpectroscopyNMR Spectroscopy
Spin-Spin SplittingSpin-Spin Splittinginin
NMR SpectroscopyNMR Spectroscopy
Dr. Wolf's CHM 201 & 202 13- 104
01.02.03.04.05.06.07.08.09.010.0
Chemical shift (Chemical shift (, ppm), ppm)
ClCl22CCHHCCHH33Figure 13.12 (page 536)Figure 13.12 (page 536)Figure 13.12 (page 536)Figure 13.12 (page 536)
4 lines;4 lines;quartetquartet
2 lines;2 lines;doubletdoublet
CCHH33CCHH
Dr. Wolf's CHM 201 & 202 13- 105
Two-bond and three-bond couplingTwo-bond and three-bond couplingTwo-bond and three-bond couplingTwo-bond and three-bond coupling
CC CC
HH
HH
CC CC HHHH
protons separated byprotons separated bytwo bondstwo bonds
(geminal relationship) (geminal relationship)
protons separated byprotons separated bythree bondsthree bonds
(vicinal relationship)(vicinal relationship)
Dr. Wolf's CHM 201 & 202 13- 106
in order to observe splitting, protons cannot in order to observe splitting, protons cannot
have same chemical shifthave same chemical shift
coupling constant (coupling constant (22J or J or 33J) is independent J) is independent
of field strengthof field strength
Two-bond and three-bond couplingTwo-bond and three-bond couplingTwo-bond and three-bond couplingTwo-bond and three-bond coupling
CC CC
HH
HH
CC CC HHHH
01.02.03.04.05.06.07.08.09.010.0
Chemical shift (Chemical shift (, ppm), ppm)
ClCl22CCHHCCHH33Figure 13.12 (page 536)Figure 13.12 (page 536)Figure 13.12 (page 536)Figure 13.12 (page 536)
4 lines;4 lines;
quartetquartet
2 lines;2 lines;
doubletdoublet
CCHH33CCHH
coupled protons are vicinal (three-bond coupling)coupled protons are vicinal (three-bond coupling)
CCHH splits C splits CHH33 into a doublet, C into a doublet, CHH33 splits C splits CHH into a quartet into a quartet
Dr. Wolf's CHM 201 & 202 13- 108
Why do the methyl protons ofWhy do the methyl protons of1,1-dichloroethane appear as a doublet?1,1-dichloroethane appear as a doublet?
Why do the methyl protons ofWhy do the methyl protons of1,1-dichloroethane appear as a doublet?1,1-dichloroethane appear as a doublet?
CC CC HHHH
ClCl
ClCl
HH
HHsignal for signal for methylmethyl protons is split into protons is split into a doubleta doublet
To explain the splitting of the To explain the splitting of the protonsprotons at C-2, at C-2, we first focus on the two possible spin we first focus on the two possible spin orientations of the orientations of the protonproton at C-1 at C-1
Dr. Wolf's CHM 201 & 202 13- 109
Why do the methyl protons ofWhy do the methyl protons of1,1-dichloroethane appear as a doublet?1,1-dichloroethane appear as a doublet?
Why do the methyl protons ofWhy do the methyl protons of1,1-dichloroethane appear as a doublet?1,1-dichloroethane appear as a doublet?
CC CC HHHH
ClCl
ClCl
HH
HHsignal for signal for methylmethyl protons is split into protons is split into a doubleta doublet
There are two orientations of the nuclear spin There are two orientations of the nuclear spin for the proton at C-1. One orientation shields for the proton at C-1. One orientation shields the protons at C-2; the other deshields the C-the protons at C-2; the other deshields the C-2 protons.2 protons.
Dr. Wolf's CHM 201 & 202 13- 110
Why do the methyl protons ofWhy do the methyl protons of1,1-dichloroethane appear as a doublet?1,1-dichloroethane appear as a doublet?
Why do the methyl protons ofWhy do the methyl protons of1,1-dichloroethane appear as a doublet?1,1-dichloroethane appear as a doublet?
CC CC HHHH
ClCl
ClCl
HH
HHsignal for signal for methylmethyl protons is split into protons is split into a doubleta doublet
The protons at C-2 "feel" the effect of both the The protons at C-2 "feel" the effect of both the applied magnetic field and the local field applied magnetic field and the local field resulting from the spin of the C-1 proton.resulting from the spin of the C-1 proton.
Dr. Wolf's CHM 201 & 202 13- 111
Why do the methyl protons ofWhy do the methyl protons of1,1-dichloroethane appear as a doublet?1,1-dichloroethane appear as a doublet?
Why do the methyl protons ofWhy do the methyl protons of1,1-dichloroethane appear as a doublet?1,1-dichloroethane appear as a doublet?
CC CC HHHH
ClCl
ClCl
HH
HH"true" chemical"true" chemical
shift of methylshift of methyl
protons (no coupling)protons (no coupling)
this line correspondsthis line corresponds
to molecules in which to molecules in which
the nuclear spin of the nuclear spin of
the proton at C-1 the proton at C-1
reinforcesreinforces
the applied fieldthe applied field
this line correspondsthis line corresponds
to molecules in which to molecules in which
the nuclear spin of the nuclear spin of
the proton at C-1 the proton at C-1
opposesopposes
the applied fieldthe applied field
Dr. Wolf's CHM 201 & 202 13- 112
Why does the methine proton ofWhy does the methine proton of1,1-dichloroethane appear as a quartet?1,1-dichloroethane appear as a quartet?
Why does the methine proton ofWhy does the methine proton of1,1-dichloroethane appear as a quartet?1,1-dichloroethane appear as a quartet?
CC CC HHHH
ClCl
ClCl
HH
HHsignal for signal for methinemethine proton is split into proton is split into a quarteta quartet
The The protonproton at C-1 "feels" the effect of the at C-1 "feels" the effect of the applied magnetic field and the local fields applied magnetic field and the local fields resulting from the spin states of the three resulting from the spin states of the three methyl protons. The possible combinations methyl protons. The possible combinations are shown on the next slide.are shown on the next slide.
Dr. Wolf's CHM 201 & 202 13- 113
CC CC HHHH
ClCl
ClCl
HH
HH There are eight combinations of There are eight combinations of nuclear spins for the three methyl nuclear spins for the three methyl protons.protons.
These 8 combinations split the These 8 combinations split the signal into a 1:3:3:1 quartet.signal into a 1:3:3:1 quartet.
Why does the methine proton ofWhy does the methine proton of1,1-dichloroethane appear as a quartet?1,1-dichloroethane appear as a quartet?
Why does the methine proton ofWhy does the methine proton of1,1-dichloroethane appear as a quartet?1,1-dichloroethane appear as a quartet?
Dr. Wolf's CHM 201 & 202 13- 114
For simple cases, the multiplicity of a signalFor simple cases, the multiplicity of a signalfor a particular proton is equal to the number for a particular proton is equal to the number of equivalent vicinal protons + 1.of equivalent vicinal protons + 1.
The splitting rule for The splitting rule for 11H NMRH NMRThe splitting rule for The splitting rule for 11H NMRH NMR
Dr. Wolf's CHM 201 & 202 13- 115
Splitting Patterns:Splitting Patterns:The Ethyl GroupThe Ethyl Group
Splitting Patterns:Splitting Patterns:The Ethyl GroupThe Ethyl Group
CHCH33CHCH22X is characterized by a triplet-quartet X is characterized by a triplet-quartet
pattern (quartet at lower field than the triplet)pattern (quartet at lower field than the triplet)
Dr. Wolf's CHM 201 & 202 13- 116
01.02.03.04.05.06.07.08.09.010.0
Chemical shift (Chemical shift (, ppm), ppm)
BrCBrCHH22CCHH33
4 lines;4 lines;quartetquartet
3 lines;3 lines;triplettriplet
CCHH33
CCHH22
Dr. Wolf's CHM 201 & 202 13- 117
Splitting Patterns of Common MultipletsSplitting Patterns of Common Multiplets
Number of equivalentNumber of equivalent AppearanceAppearance Intensities of linesIntensities of linesprotons to which H protons to which H of multipletof multiplet in multipletin multipletis coupledis coupled
11 DoubletDoublet 1:11:1
22 TripletTriplet 1:2:11:2:1
33 QuartetQuartet 1:3:3:11:3:3:1
44 PentetPentet 1:4:6:4:11:4:6:4:1
55 SextetSextet 1:5:10:10:5:11:5:10:10:5:1
66 SeptetSeptet 1:6:15:20:15:6:11:6:15:20:15:6:1
Table 13.2 (page 540)Table 13.2 (page 540)Table 13.2 (page 540)Table 13.2 (page 540)
Dr. Wolf's CHM 201 & 202 13- 118
Splitting Patterns:Splitting Patterns:The Isopropyl GroupThe Isopropyl GroupSplitting Patterns:Splitting Patterns:
The Isopropyl GroupThe Isopropyl Group
(CH(CH33))22CHX is characterized by a doublet-septet CHX is characterized by a doublet-septet
pattern (septet at lower field than the doublet)pattern (septet at lower field than the doublet)
Dr. Wolf's CHM 201 & 202 13- 119
01.02.03.04.05.06.07.08.09.010.0
Chemical shift (Chemical shift (, ppm), ppm)
BrCBrCHH(C(CHH33))22
7 lines;7 lines;septetseptet
2 lines;2 lines;doubletdoublet
CCHH33
CCHH
Dr. Wolf's CHM 201 & 202 13- 120
1313C NMR SpectroscopyC NMR Spectroscopy1313C NMR SpectroscopyC NMR Spectroscopy
Dr. Wolf's CHM 201 & 202 13- 121
11H and H and 1313C NMR compared:C NMR compared:11H and H and 1313C NMR compared:C NMR compared:
both give us information about the number of both give us information about the number of chemically nonequivalent nuclei chemically nonequivalent nuclei (nonequivalent hydrogens or nonequivalent (nonequivalent hydrogens or nonequivalent carbons)carbons)
both give us information about the both give us information about the environment of the nuclei (hybridization state, environment of the nuclei (hybridization state, attached atoms, etc.)attached atoms, etc.)
it is convenient to use FT-NMR techniques for it is convenient to use FT-NMR techniques for 11H; it is standard practice for H; it is standard practice for 1313C NMRC NMR
Dr. Wolf's CHM 201 & 202 13- 122
11H and H and 1313C NMR compared:C NMR compared:11H and H and 1313C NMR compared:C NMR compared:
1313C requires FT-NMR because the signal for a C requires FT-NMR because the signal for a carbon atom is 10carbon atom is 10-4-4 times weaker than the times weaker than the signal for a hydrogen atomsignal for a hydrogen atom
a signal for a a signal for a 1313C nucleus is only about 1% as C nucleus is only about 1% as intense as that for intense as that for 11H because of the magnetic H because of the magnetic properties of the nuclei, andproperties of the nuclei, and
at the "natural abundance" level only 1.1% of at the "natural abundance" level only 1.1% of all the C atoms in a sample are all the C atoms in a sample are 1313C (most are C (most are 1212C)C)
Dr. Wolf's CHM 201 & 202 13- 123
11H and H and 1313C NMR compared:C NMR compared:11H and H and 1313C NMR compared:C NMR compared:
1313C signals are spread over a much wider C signals are spread over a much wider range than range than 11H signals making it easier to H signals making it easier to identify and count individual nucleiidentify and count individual nuclei
Figure 13.23 (a) shows the Figure 13.23 (a) shows the 11H NMR spectrum H NMR spectrum of 1-chloropentane; Figure 13.23 (b) shows of 1-chloropentane; Figure 13.23 (b) shows the the 1313C spectrum. It is much easier to identify C spectrum. It is much easier to identify the compound as 1-chloropentane by its the compound as 1-chloropentane by its 1313C C spectrum than by its spectrum than by its 11H spectrum.H spectrum.
Dr. Wolf's CHM 201 & 202 13- 124
01.02.03.04.05.06.07.08.09.010.0
Chemical shift (Chemical shift (, ppm), ppm)
ClClCCHH22 CCHH33ClClCCHH22CHCH22CHCH22CHCH22CCHH33
11HH
Dr. Wolf's CHM 201 & 202 13- 125Chemical shift (Chemical shift (, ppm), ppm)
ClClCHCH22CHCH22CHCH22CHCH22CHCH33
020406080100120140160180200
1313CC
CDClCDCl33
a separate, distinct a separate, distinct peak appears for peak appears for each of the 5 carbonseach of the 5 carbons
Dr. Wolf's CHM 201 & 202 13- 126
1313C Chemical ShiftsC Chemical Shifts1313C Chemical ShiftsC Chemical Shifts
are measured in ppm (are measured in ppm ())
from the carbons of TMSfrom the carbons of TMS
Dr. Wolf's CHM 201 & 202 13- 127
1313C Chemical shifts are most affected by:C Chemical shifts are most affected by:1313C Chemical shifts are most affected by:C Chemical shifts are most affected by:
electronegativity of groups attached to carbonelectronegativity of groups attached to carbon
hybridization state of carbonhybridization state of carbon
Dr. Wolf's CHM 201 & 202 13- 128
Electronegativity EffectsElectronegativity EffectsElectronegativity EffectsElectronegativity Effects
Electronegativity has an even greater effect Electronegativity has an even greater effect on on 1313C chemical shifts than it does on C chemical shifts than it does on 11H H chemical shifts.chemical shifts.
Dr. Wolf's CHM 201 & 202 13- 129
Types of CarbonsTypes of CarbonsTypes of CarbonsTypes of Carbons
(CH(CH33))33CCHH
CCHH44
CCHH33CCHH33
CHCH33CCHH22CHCH33
(CH(CH33))44CC
primaryprimary
secondarysecondary
tertiarytertiary
quaternaryquaternary
ClassificationClassification Chemical shift, Chemical shift, 11HH 1313CC
0.20.2
0.90.9
1.31.3
1.71.7
-2-2
88
1616
2525
2828
Replacing H by C (more electronegative) deshieldsReplacing H by C (more electronegative) deshieldsC to which it is attached.C to which it is attached.
Dr. Wolf's CHM 201 & 202 13- 130
Electronegativity effects on CHElectronegativity effects on CH33Electronegativity effects on CHElectronegativity effects on CH33
CCHH33FF
CCHH44
CCHH33NHNH22
CCHH33OHOH
Chemical shift, Chemical shift, 11HH
0.20.2
2.52.5
3.43.4
4.34.3
1313CC
-2-2
2727
5050
7575
Dr. Wolf's CHM 201 & 202 13- 131
Electronegativity effects and chain lengthElectronegativity effects and chain lengthElectronegativity effects and chain lengthElectronegativity effects and chain length
ChemicalChemicalshift, shift,
ClCl CHCH22 CHCH22 CHCH22 CHCH22 CHCH33
4545 3333 2929 2222 1414
Deshielding effect of Deshielding effect of ClCl decreases as decreases as number of bonds between number of bonds between ClCl and C increases. and C increases.
Dr. Wolf's CHM 201 & 202 13- 132
1313C Chemical shifts are most affected by:C Chemical shifts are most affected by:1313C Chemical shifts are most affected by:C Chemical shifts are most affected by:
electronegativity of groups attached to carbonelectronegativity of groups attached to carbon
hybridization state of carbonhybridization state of carbon
Dr. Wolf's CHM 201 & 202 13- 133
Hybridization effectsHybridization effectsHybridization effectsHybridization effects
spsp33 hybridized hybridized carbon is more carbon is more shielded than shielded than spsp22
114114
138138
3636
3636 126-142126-142
spsp hybridized hybridized carbon is carbon is more more shielded than shielded than spsp22, but less , but less shielded than shielded than spsp33
CHCH33HH CC CC CHCH22 CHCH22
6868 8484 2222 2020 1313
Dr. Wolf's CHM 201 & 202 13- 134
Carbonyl carbons are especially deshieldedCarbonyl carbons are especially deshieldedCarbonyl carbons are especially deshieldedCarbonyl carbons are especially deshielded OO
CHCH22 CC OO CHCH22 CHCH33
127-134127-1344141 14146161171171
Dr. Wolf's CHM 201 & 202 13- 135
Table 13.3 (p 549)Table 13.3 (p 549)Table 13.3 (p 549)Table 13.3 (p 549)
Type of carbonType of carbon Chemical shift (Chemical shift (),),ppmppm
Type of carbonType of carbon Chemical shift (Chemical shift (),),ppmppm
RRCCHH33 0-350-35
CCRR22RR22CC
65-9065-90CCRRRRCC
RR22CCHH22 15-4015-40
RR33CCHH 25-5025-50
RR44CC 30-4030-40
100-150100-150 110-175110-175
Dr. Wolf's CHM 201 & 202 13- 136
Table 13.3 (p 549)Table 13.3 (p 549)Table 13.3 (p 549)Table 13.3 (p 549)
Type of carbonType of carbon Chemical shift (Chemical shift (),),ppmppm
Type of carbonType of carbon Chemical shift (Chemical shift (),),ppmppm
RRCCHH22BrBr 20-4020-40
RRCCHH22ClCl 25-5025-50
35-5035-50RRCCHH22NHNH22
50-6550-65RRCCHH22OHOH
RRCCHH22OROR 50-6550-65
RRCCOROR
OO
160-185160-185
RRCCRR
OO
190-220190-220
RRCC NN 110-125110-125
Dr. Wolf's CHM 201 & 202 13- 137
1313C NMR and Peak IntensitiesC NMR and Peak Intensities1313C NMR and Peak IntensitiesC NMR and Peak Intensities
Pulse-FT NMR distorts intensities of signals. Pulse-FT NMR distorts intensities of signals. Therefore, peak heights and areas can be Therefore, peak heights and areas can be deceptive.deceptive.
Dr. Wolf's CHM 201 & 202 13- 138
CHCH33
OHOH
Figure 13.24 (page 551)Figure 13.24 (page 551)Figure 13.24 (page 551)Figure 13.24 (page 551)
Chemical shift (Chemical shift (, ppm), ppm)
020406080100120140160180200
7 carbons give 7 7 carbons give 7 signals, but signals, but intensities are not intensities are not equalequal
Dr. Wolf's CHM 201 & 202 13- 139
End of Chapter 13End of Chapter 13