2. Principles of Spectroscopy UV and IR - Copy - Copy

8/6/2019 2. Principles of Spectroscopy UV and IR - Copy - Copy

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by

UV, IR, NMR AND MASS SPECTROMETRIES

Identification of Compounds


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Gas Chromatogram of Flavor Compounds

5

1516

1

10 11

13

17

9

3

6

7

8

14

12


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Identification of Compound

H2

CH3

CH3

CH3

H3C

H2 H

HH

HH

O


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SPECTROMETRIC IDENTIFICATION

I. Introduction of Spectrometric AnalysesII. Ultra Violet Spectrometry

III. Infrared Spectrometry

IV. Nuclear Magnetic Resonance Spectrometry

V. Mass Spectrometry


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I. Introduction of Spectrometric Analyses

The study how the sample interacts with different

wavelength in a given region of electromagnetic radiation

is called spectroscopy or spectrochemical analysis.

The collection of measurements signals (absorbance) as a

function of electromagnetic radiation is called a spectrum.


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Spectrum of Radiation


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Electromagnetic Spectrum.

Wavelength,, cm

frequency, , (cycles/sec)

-ray

-ray

ultravio

let

visibl

e

infrare

d

microwave

radio

violet

blue

green

yellow

orange

red visible region

400 500 600 700 800

1020

1018

1016

1014

1012

1010

108

106

104

102

10-10

10-8

10-6

10-4

10-2

1

102

104

106

108

Wavelength,, nm


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Energy Absorption

The mechanism of absorption energy is different in the

Ultraviolet, Infrared, and Nuclear Magnetic Resonance

regions. However, the fundamental process is the absorptionof certain amount of energy.

The energy required for the transition from a state of lower

energy to a state of higher energy is directly related to the

frequency of electromagnetic radiation that causes the

transition.


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Spectral Distribution of Radiant Energy

V' = Wave number (cm-1

) = Wave length (nm)C = Velocity of Radiation (constant) 3 1010 cm/secV = Frequency of Radiation (cycles/sec)

V' = =

(The energy of photon) E = Vh(Planck's Constant 6.62 10-27 erg - sec )

E = Vh = h

C = V

V =

C

V

1

C

C

1 x 107erg = I joule

=0.239 calorie

Avogadros number = 6.02

x 10 23 mol-1


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Visible

Ultra

violet

Radio

Gamma

ray

EnergyWave

Number VWavelength

Frequency

TypeRadiation

Typespectroscopy

TypeQuantum Transition

Kcal/mol

Electronvolts,

eV cm-1

cm Hz

9.4 x 107 4.9 x 106 3.3 x 1010 3 x 10-11 1021

9.4 x 103 4.9 x 102 3.3 x 106 3 x 10-7 1017

9.4 x 101 4.9 x 100 3.3 x 104 3 x 10-5 1015

9.4 x 10-1 4.9 x 10-2 3.3 x 102 3 x 10-3 1013

9.4 x 10-3 4.9 x 10-4 3.3 x 100 3 x 10-1 1011

9.4 x 10-7 4.9 x 10-8 3.3 x 10-4 3 x 103 107

X-ray

Infrared

Micro-

wave

Gamma ray

emission

X-rayabsorption,

emission

UV absorption

IR absorption

Microwave

absorption

Nuclear

magnetic

resonance

Nuclear

Electronic(inner shell)

Molecular

vibration

Electronic

(outer shell)

Molecularrotation

Magnetically

induced spin

states

Spectral Properties, Application and Interactions of Electromagnetic Radiation


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Molecular Orbital of Triplet Oxygen

MolecularAtomicAtomic

2Pz 2Py 2Px2Px 2Py 2Pz

*

* *

2S2S

1S1S

*

*

Energy


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Principal quantum number (n): The average distance of the

electron from the nucleus. 1, 2, and so on.

Azimuthal quantum number (Momentum quantum number)

(l): The shape of the orbital. 1s, 2s, 2p, 3s, 3p, 3d, etc

Magnetic quantum number (Orientational quantum number)

(ml): The orientation of orbital in the space. 2px 2py, 2pz x, y

and z are orientational quantum number

Electron spin quantum number (ms)= The two possible

orientation of the electron in a magnetic field. 1/2 or 1/2

Quantum Numbers and Orbitals


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One S and Three P Orbitals


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The 5 d Orbitals


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II. Ultra Violet Spectrometry

The absorption of ultraviolet radiation by

molecules is dependent upon the electronicstructure of the molecule. So the ultraviolet

spectrum is called electronic spectrum.


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Visible

Ultra

violet

Radio

Gamma

ray

EnergyWave

Number VWavelength

Frequency

TypeRadiation

Typespectroscopy


Kcal/mol

Electronvolts,

eV cm-1

cm Hz

9.4 x 107 4.9 x 106 3.3 x 1010 3 x 10-11 1021

9.4 x 103 4.9 x 102 3.3 x 106 3 x 10-7 1017

9.4 x 101 4.9 x 100 3.3 x 104 3 x 10-5 1015

9.4 x 10-1 4.9 x 10-2 3.3 x 102 3 x 10-3 1013

9.4 x 10-3 4.9 x 10-4 3.3 x 100 3 x 10-1 1011

9.4 x 10-7 4.9 x 10-8 3.3 x 10-4 3 x 103 107

X-ray

Infrared

Micro-

wave

Gamma ray

emission

X-rayabsorption,

emission

UV absorption

IR absorption

Microwave

absorption

Nuclear

magnetic

resonance

Nuclear

Electronic(inner shell)

Molecular

vibration

Electronic

(outer shell)

Molecularrotation

Magnetically

induced spin

states



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Electronic Excitation

The absorption of light energy by organic compounds in the

visible and ultraviolet region involves the promotion ofelectrons in , , and n-orbitals from the ground state tohigher energy states . This is also called Energy Transition.

These higher energy states are molecular orbitals called

antibonding.


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Types of Bonds

Energy

*

*

n

*

*

n

*

n

*

Antibonding

Antibonding

Nonbonding

Bonding

Bonding


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Electronic Molecular Energy Levels

The higher energy transitions ( *) occur a shorter

wavelength and the low energy transitions ( *, n *) occur at longer wavelength.


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Electronic Ground and Excitation States

* *

hv

*

hv

*

n

hv

*

hv

*

n

*

Energy


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Chromophore is a functional group which absorbs a

characteristic ultraviolet or visible region.

210 nm Double Bonds

233 nm Conjugated Diene268 nm Conjugated Triene

315 nm Conjugated Tetraene

and* orbitals and* orbitals

Chromophore


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III. Infrared Spectrometry

Radiation energy in the infrared region is absorbed by the

organic compound and converted into energy of molecular

vibration.

The energy absorption pattern thus obtained is commonly

referred to as an infrared spectrum which has the plot of

intensity of radiation absorption versus wavelength ofabsorption.


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Visible

Ultra

violet

Radio

Gamma

ray

EnergyWave

Number VWavelength

Frequency

TypeRadiation

Typespectroscopy


Kcal/mol

Electronvolts,eV cm-1

cm Hz

9.4 x 107 4.9 x 106 3.3 x 1010 3 x 10-11 1021

9.4 x 103

4.9 x 102

3.3 x 106

3 x 10-7

1017

9.4 x 101 4.9 x 100 3.3 x 104 3 x 10-5 1015

9.4 x 10-1 4.9 x 10-2 3.3 x 102 3 x 10-3 1013

9.4 x 10-3 4.9 x 10-4 3.3 x 100 3 x 10-1 1011

9.4 x 10-7 4.9 x 10-8 3.3 x 10-4 3 x 103 107

X-ray

Infrared

Micro-

wave

Gamma ray

emission

X-ray

absorption,

emission

UV absorption

IR absorption

Microwave

absorption

Nuclear

magnetic

resonance

Nuclear

Electronic

(inner shell)

Molecular

vibration

Electronic

(outer shell)

Molecular

rotation

Magnetically

induced spin

states



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Some Molecular Vibrations

C C

O

O HH

H

H

Stretch

Unsymmetrical bend

Symmetrical bend


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Atom, Group, and Molecular Rotations

C C

O

O

HH

H

H

X

YZ

OH group rotation

H atom rotation COOH group rotation

CH3

group rotation

Molecular rotation

Center of gravity of themolecule is at the origin


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Infrared Spectrum


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Infrared Absorption and Functional Groups

3.4 m Alkane

6.0 m cis-Double Bond10.3 m trans-Double Bond5.8 m Carbonyl3.7 m Hydroxyl Stretching of Acid Group2.9 m Hydroxyl

2. Principles of Spectroscopy UV and IR - Copy - Copy

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