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

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

13.113.1

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 Radiation

Dr. Wolf's CHM 201 & 202 13- 4

Figure 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

13.213.2Principles 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 = 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?

Dr. Wolf's CHM 201 & 202 13- 10

13.20 - 13.2213.20 - 13.22

Infrared 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 Spectroscopy

Dr. Wolf's CHM 201 & 202 13- 12

Stretching 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 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 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 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

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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

13.2313.23

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 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-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-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

HOMOHOMO

LUMOLUMO

EE = = hh

Dr. Wolf's CHM 201 & 202 13- 31

* 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

LycopeneLycopene


orange-red pigment in tomatoesorange-red pigment in tomatoes

Dr. Wolf's CHM 201 & 202 13- 36

13.2413.24

Mass 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 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

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 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

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 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

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

13.2513.25

Molecular FormulaMolecular Formula

as aas a

Clue to StructureClue to Structure

Dr. Wolf's CHM 201 & 202 13- 55

Molecular 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 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 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 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 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 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 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 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 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 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 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- 1 chapter 13 spectroscopy infrared spectroscopy...

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