dr. wolf's chm 201 & 202 13- 1 chapter 13 spectroscopy infrared spectroscopy...

Dr. Wolf's CHM 201 & 202 13- 1

Chapter 13Chapter 13

SpectroscopySpectroscopy

Chapter 13Chapter 13


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


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


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


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


Stretching vibrations (multiple bonds)Stretching vibrations (multiple bonds)


CC CC 1620-16801620-1680

——CC NN

——CC C—C— 2100-22002100-2200

2240-22802240-2280

Dr. Wolf's CHM 201 & 202 13- 19


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


CC OO

Dr. Wolf's CHM 201 & 202 13- 20


Bending vibrations of alkenesBending vibrations of alkenes


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


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


Dr. Wolf's CHM 201 & 202 13- 22

2000200035003500 30003000 25002500 1000100015001500 500500


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


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


Dr. Wolf's CHM 201 & 202 13- 24

2000200035003500 30003000 25002500 1000100015001500 500500


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


Dr. Wolf's CHM 201 & 202 13- 25

2000200035003500 30003000 25002500 1000100015001500 500500


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


Dr. Wolf's CHM 201 & 202 13- 26

Ultraviolet-Visible (UV-VIS) Ultraviolet-Visible (UV-VIS)


Ultraviolet-Visible (UV-VIS) Ultraviolet-Visible (UV-VIS)


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


CHCH33


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


(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


conjugated conjugated trienetriene plus plus two methyl groupstwo methyl groups

Dr. Wolf's CHM 201 & 202 13- 35

LycopeneLycopeneLycopeneLycopene


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


electron is deflected but transfers much of its electron is deflected but transfers much of its energy to the moleculeenergy to the molecule

ee––


Dr. Wolf's CHM 201 & 202 13- 39


electron is deflected but transfers much of its electron is deflected but transfers much of its energy to the moleculeenergy to the molecule

ee––


Dr. Wolf's CHM 201 & 202 13- 40

This energy-rich species ejects an electron.This energy-rich species ejects an electron.


Dr. Wolf's CHM 201 & 202 13- 41

This energy-rich species ejects an electron.This energy-rich species ejects an electron.


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


++••

Dr. Wolf's CHM 201 & 202 13- 43


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.


++••

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.


++ ••

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


++

++++

++

+

+

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

++ ++ ++ ++

+ +


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


112112

114114

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


7777



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


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


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


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


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


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


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


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 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


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


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


Effects of Molecular StructureEffects of Molecular Structureonon


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


But protons attached to sp hybridized carbonBut protons attached to sp hybridized carbonare more shielded than those attachedare more shielded than those attached


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


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



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


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


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


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


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?


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



CC CC HHHH

ClCl

ClCl

HH


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



CC CC HHHH

ClCl

ClCl

HH


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



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?


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.



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


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


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


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


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


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


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)



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)


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

dr. wolf's chm 201 & 202 13- 1 chapter 13 spectroscopy infrared spectroscopy...

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