Chapter 12 - Infrared Spectroscopy and Mass Spectrometry (1)

8/18/2019 Chapter 12 - Infrared Spectroscopy and Mass Spectrometry (1)

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Chapter 12

Infrared Spectroscopy andMass Spectrometry

Jo BlackburnRichland College, allas, !"

allas County Community College istrict 2##$, %rentice &all

Organic Chemistry , 'th (dition

)* +* ade, Jr*


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Chapter 12 3

!ypes of Spectroscopy

- Infrared IR spectroscopy measures the bond

0ibration fre.uencies in a molecule and is used

to determine the functional group*

- Mass spectrometry MS fragments the moleculeand measures the masses*

- 3uclear magnetic resonance 3MR

spectroscopy detects signals from hydrogen

atoms and can be used to distinguish isomers*

- 4ltra0iolet 45 spectroscopy uses electron

transitions to determine bonding patterns* =>


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Chapter 12 4

(lectromagnetic

Spectrum- (6amples7 " rays, micro/a0es, radio

/a0es, 0isible light, IR, and 45*

- 8re.uency and /a0elength are

in0ersely proportional*

- c 9 λν , /here c is the speed of light*

- (nergy per photon 9 hν , /here h is

%lanck:s constant* =>


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Chapter 12 5

!he Spectrum and

Molecular (ffects

=>

9;


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Chapter 12 6

!he IR Region

- Just belo/ red in the 0isible region*

- a0elengths usually 2*'


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Chapter 12 7

Molecular 5ibrations

Co0alent bonds 0ibrate at only certain

allo/able fre.uencies*

=>


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Chapter 12 8

Stretching 8re.uencies

- 8re.uency decreases /ith increasingatomic /eight*

- 8re.uency increases /ith increasing

bond energy* =>


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Chapter 12 9

5ibrational Modes

3onlinear molecule /ith n atoms usually has

$n < = fundamental 0ibrational modes*

=>


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Chapter 12 10

8ingerprint of Molecule

- holeed*

- 3o t/o molecules /ill gi0e e6actly the

same IR spectrum e6cept enantiomers*

- Simple stretching7 1=##


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Chapter 12 11

IR


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Chapter 12 12

n Infrared

Spectrometer

=>


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Chapter 12 13

8!


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Chapter 12 14

Carbon


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Chapter 12 15

Carbon


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Chapter 12 16

n lkane IR Spectrum

=>


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Chapter 12 17

n lkene IR Spectrum

=>


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Chapter 12 18

n lkyne IR Spectrum

=>


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Chapter 12 19

E


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Chapter 12 20

n lcohol IR Spectrum

=>


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Chapter 12 21

n mine

IR Spectrum

=>


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Chapter 12 22

Carbonyl Stretching

- !he C9E bond of simple ketones,

aldehydes, and carbo6ylic acids absorb

around 1F1# cm


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Chapter 12 23

Getone

IR Spectrum

=>


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Chapter 12 24

n ldehyde

IR Spectrum

=>


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Chapter 12 25

E


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Chapter 12 26

5ariations in

C9E bsorption- Conugation of C9E /ith C9C lo/ers thestretching fre.uency to H1=D# cm


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Chapter 12 27

n mide

IR Spectrum

=>


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Chapter 12 28

Carbon < 3itrogen

Stretching- C < 3 absorbs around 12## cm


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Chapter 12 29

3itrile

IR Spectrum

=>


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Chapter 12 30

Summary of IR

bsorptions

=>9;


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Chapter 12 31

Strengths and )imitations

- IR alone cannot determine a structure*

- Some signals may be ambiguous*

- !he functional group is usually indicated*- !he absence of a signal is definite proof

that the functional group is absent*

- Correspondence /ith a kno/n sample:sIR spectrum confirms the identity of the

compound* =>


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Chapter 12 32

Mass Spectrometry

- Molecular /eight can be obtained from a0ery small sample*

- It does not in0ol0e the absorption or

emission of light*- beam of high


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Chapter 12 34

Separation of Ions

- Enly the cations are deflected by the

magnetic field*

- mount of deflection depends on m/z *

- !he detector signal is proportional to

the number of ions hitting it*

- By 0arying the magnetic field, ions of all

masses are collected and counted* =>


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Chapter 12 35

Mass Spectrometer

=>


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Chapter 12 36

!he Mass Spectrum

Masses are graphed or tabulated according to

their relati0e abundance*

=>


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Chapter 12 37

!he +C

mi6ture of compounds is separatedby gas chromatography, then identified

by mass spectrometry*


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Chapter 12 38

&igh Resolution MS

- Masses measured to 1 part in 2#,###*

- molecule /ith mass of ?? could be

C$&D, C2&?E, CE2, or C32&?*- If a more e6act mass is ??*#2, pick the

correct structure from the table7

C$&D C2&?E CE2 C32&?

??*#=2=# ??*#2=2# ?$*DD$ ??*#$F?#

9;


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Chapter 12 40

Isotopic bundance

=>

81Br


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Chapter 12 41

Mass Spectrum

/ith Sulfur

=>


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Chapter 12 42

Mass Spectrum

/ith Chlorine

=>


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Chapter 12 43

Mass Spectrum

/ith Bromine

=>


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Chapter 12 44

Mass Spectra

of lkanesMore stable carbocations /ill be moreabundant*

=>

Mass Spectra


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Chapter 12 45

Mass Spectra

of lkenes

Resonanceed cations fa0ored*

=>

M S t


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Chapter 12 46

Mass Spectra

of lcohols- lcohols usually lose a /ater molecule*

- MI may not be 0isible*

=>


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(nd of Chapter 12

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Chapter 12 - Infrared Spectroscopy and Mass Spectrometry (1)