Transcript I Infra RED Spectroscopy

M. Phil (Chemistry)
M. Phil Course:
(Chemistry)
Unit:
Unit I- I
Infra RED Spectroscopy
Syllabus:
Vibrational Frequencies
Identification of functional groups
Finger Print Region
Factors affecting Vibrational frequencies
Intra and Inter Molecular Hydrogen Bonding
Far IR Region
MPC102 – PHYSICAL METHODS IN CHEMISTRY
Dr. K. SIVAKUMAR
Department of Chemistry
SCSVMV University
[email protected]

Electromagnetic Waves - Terminologies
Electromagnetic wave parameters:
Wavelength (λ): Wavelength is the distance between the consecutive peaks or crests
Wavelength is expressed in nanometers (nm)
1nm = 10-9 meters = 1/1000000000 meters
1A = 10-10 meters = 1/10000000000 meters
2

Electromagnetic Waves - Terminologies
Electromagnetic wave parameters:
Frequency (): Frequency is the number of waves passing through any point per second.
Frequency is expressed in Hertz (Hz)
3

Electromagnetic Waves - Terminologies
Electromagnetic wave parameters:
Wave number ( ): Wave number is the number of waves per cm.
Wavelength, Wave number and Frequency are interrelated as,
1
Where,

 =

c
 is wave length

is wave number
 is frequency
c is velocity of light in vacuum. i.e., 3 x 108 m/s
4
Electromagnetic Spectral regions
nm
EM
waves
10-4 to 10-2
g-rays
10-2 to 100
X-rays
100 to 102
102 to 103
103 to 105
UV
Visible
IR
105 to 107
107 to 109
Microwave Radio
5
Electromagnetic Spectrum
E = h
h – Planck’s constant
6
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The Electromagnetic wave lengths & Some examples
7
Electromagnetic radiation sources
EM radiation
Gamma rays
X-rays
Ultraviolet
Visible
Infrared
Microwave
Radio wave
Spectral method
Gamma spec.
X-ray spec.
UV spec.
Visible spec.
IR spec.
ESR spec.
NMR spec.
Radiation source
gamma-emitting nuclides
Synchrotron Radiation Source (SRS),
Betatron (cyclotron)
Hydrogen discharge lamp
tungsten filament lamp
rare-earth oxides rod
klystron valve
magnet of stable field strength
8
Electromagnetic Spectrum – Type of radiation and Energy change involved
9
Electromagnetic Spectrum – Type of radiation and Energy change involved
10
Electromagnetic Spectrum – Type of radiation and Energy change involved
11
Effect of electromagnetic radiations on chemical substances
The absorption spectrum of an atom often contains sharp and clear lines.
Absorption spectrum of an atom; Hydrogen
Energy levels in atom; Hydrogen
12
Effect of electromagnetic radiations on chemical substances
But, the absorption spectrum of a molecule is highly complicated with closely
packed lines
This is due to the fact that molecules have large number of energy levels and
certain amount of energy is required for transition between these energy levels.
Energy levels in molecule
Absorption spectrum of a molecule; Eg: H2O
13
Effect of electromagnetic radiations on chemical substances
The radiation energies absorbed by molecules may produce Rotational,
Vibrational and Electronic transitions.
14
Effect of electromagnetic radiations on chemical substances
Rotational transition
Microwave and far IR radiations bring about changes in the rotational energies
of the molecule
Example: Rotating HCl molecule
15
Effect of electromagnetic radiations on chemical substances
Vibrational transition
Infrared radiations bring about changes in the vibration modes (stretching,
contracting and bending) of covalent bonds in a molecule
Examples:
Example: Vibrating HCl molecule
16
Effect of electromagnetic radiations on chemical substances
Electronic transition
UV and Visible radiations bring about changes in the electronic transition of a molecule
Example: Cl2 in ground and excited states
17
Effect of electromagnetic radiations on chemical substances
Cl2 in Ground state
18
Effect of electromagnetic radiations on chemical substances
Cl2 in Excited state
19
Infra RED Spectral region
• Infrared refers to that part of the electromagnetic spectrum between the visible and
microwave regions.
• The IR region is divided into three regions as given below,
Few absorptions of organic molecules
‘E’ corresponds to differences
observed between vibrational states
Very few absorptions occur here
20
Infra RED Spectroscopy – Wave number
•
•
In IR, frequency is expressed as wave numbers
Wave numbers have units of reciprocal cm (cm-1)
1
1
Wavenumber in cm =
=
x 104
 in cm  in m
1
•
•
Using this scale, the IR region is 4000-400 cm-1
The corresponding wavelength range is 2.5 m to 25 m
2.5 m = 4000 cm-1
25 m = 400 cm-1
21
Infra RED Spectroscopy – Wave number…
Therefore,
HIGHER WAVENUMBER
LOWER WAVENUMBER
Higher frequency
Lower frequency
Higher energy
Lower energy
Shorter wavelength
Longer wavelength
Energy, frequency, and wavenumber are directly proportional to each other.
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22
Infra RED Spectroscopy – An IR spectrum
• In IR spectroscopy, an organic molecule is exposed to IR radiation. When the radiant
energy matches the energy of a specific molecular vibration, absorption occurs.
• Compares intensity of IR striking sample (Iin) with intensity of IR leaving sample (Iout)
• 100%T no light absorbed by sample
• 0% all light absorbed by sample
23
Infra RED Spectroscopy – An IR spectrum
•An IR spectrum is a graph between Wavenumber (in cm-1) Vs Transmittance (%).
IR spectrum of
octane
An absorption of IR energy is therefore represented by a “trough” in the curve.
24
Infra RED Spectroscopy – An IR spectrum…
• Band intensities can also be expressed as absorbance; A = log10 (1/T)
IR spectrum of
octane
25
Infra RED Spectroscopy – Principle
• Molecules are flexible.
• Atoms in organic molecules are constantly vibrating around average positions.
• Therefore, A vibrating bond can be thought of as two masses connected by a spring.
• Molecules are vibrating in different modes i.e., different ways.
• Bond lengths and bond angles are continuously changing due to this vibration.
• These vibrational changes depend on the spatial arrangement and masses of the atoms in
that particular molecule.
26
Infra RED Spectroscopy – Principle…
• If infrared radiations are passed through the naturally vibrating molecules then IR waves matching with the
vibrating
frequencies
of
molecule
will
be
absorbed
and
increases the amplitude
of vibration in molecules.
• Because, IR radiations does not have sufficient energy to cause the excitation of electrons, however, it causes
atoms and groups of atoms of organic compounds to vibrate faster about the covalent bonds which connect
them.
• The IR spectrum (vibrational spectra) appears as band and not as line because; the vibrational changes are
also accompanied by several numbers of rotational changes.
27
Infra RED Spectroscopy –Functional group & Finger print region
• Every molecule absorbs IR waves at particular frequencies and produces absorption bands.
• There are two sections in the IR spectra.
Functional group region > 1500cm-1
Fingerprint region < 1500cm-1
Fingerprint region: The absorption band in the finger print region is due to the complex
vibrations involving in entire molecules. It is impossible for any two different compounds (except
enantiomers) to have precisely the same infrared spectrum. The pattern of absorptions in this
regions are unique to any particular compound, just as a person’s fingerprints are unique.
28
Infra RED Spectroscopy – Finger print region can be subdivided in to three regins
(i) 1500 – 1350cm-1 region:
•
The absorption bands near 1380cm-1 and 1365cm-1 show the
presence of tertiary butyl group in the compound.
•
Gem-dimethyl shows a medium band near 1380cm-1
•
Nitro compounds show one strong band at 1350cm-1
(ii) 1350 – 1000cm-1 region:
•
Compounds like alcohol, esters, lactones, acid anhydrides show characteristic absorptions in
this region, due to the C-H stretching.
•
Primary alcohols form two strong bands at 1350-1260cm-1 and near 1050cm-1.
•
Phenols absorb near 1200cm-1
•
Esters show two strong bands between 1380-1050cm-1. Absorption bands in the region
1150-1070cm-1 is due to C-O and C-O-C group in ethers.
(iii) Below 1000cm-1 region:
•
The bands at  700cm-1 and at 970-960cm-1 are useful to distinguish between cis and trans
alkenes. The higher value indicates that the hydrogen atoms in the alkene are trans w.r.t. each
other.
•
The presence of mono substituted and also disubstituted (at ortho, para and meta positions)
benzene shows characteristic absorptions in this region.
•
Example: A band in the region 750-700cm-1 is due to mono substituted benzene.
29
Infra RED Spectroscopy –Functional group region
Functional group region: Like molecules, different functional groups absorb IR waves at
particular frequencies and produces absorption bands in the IR spectrum. For example, the IR
spectrum of all compounds with carbonyl group consists of absorption band in wave number range
1800cm-1 and 1650cm-1.
•
4000-2500 cm-1 N-H, C-H, O-H (stretching)
– 3300-3600 cm-1 N-H, O-H
– 3000 cm-1 C-H
•
2500-2000 cm-1 CC and CN (stretching)
•
2000-1500 cm-1 double bonds (stretching)
– 1680-1750 cm-1 C=O
– 1640-1680 cm-1 C=C
•
Below 1500 cm-1 “fingerprint” region
30
Infra RED Spectroscopy –Functional group & Finger print region…
Functional group
region
Fingerprint
region
31
Infra RED Spectroscopy –Functional group & Finger print region…
32
Infra RED Spectroscopy –Functional group & Finger print region…
33
Infra RED Spectroscopy –Functional group & Finger print region…
34
Infra RED Spectroscopy –Functional group & Finger print region…
35
Infra RED Spectroscopy – IR Active and IR Inactive
For a molecule to absorb infra red radiation, the molecule has to fulfill the following two
requirements.
1. Correct wavelength of radiation
The molecule absorbs IR radiations only when the natural frequency of vibration of atoms or
groups of atoms or functional groups of molecule is same as the frequency of the incident
radiation. i.e., If infrared radiations are passed through the naturally vibrating molecules then
IR waves matching with the vibrating frequencies of molecule will be absorbed and increases
the amplitude of vibration in molecules.
For example: The natural frequency of HCl is
8.7  1013 sec1
When IR radiation is passed through the HCl and the spectrum is recorded. The spectrum
consists of a absorption band at a frequency 8.7  1013 sec1
Hence,
8.7  1013 sec1

is the natural or characteristic frequency of the HCl molecule.
  2.886  10 cm
3
1
36
Infra RED Spectroscopy – IR Active and IR Inactive…..
2. Electric dipole 
For absorbing IR radiations a molecule should
possess electric dipole (dipole moment) and the
absorption should causes change in electric dipole.
Molecules with electric dipole will have slight positive
and slight negative charge on its component atoms.
For example:
In HCl, due to the high electro
negativity of Cl, the electron clouds will be more
towards chlorine and less towards hydrogen. So,
hydrogen will get slight positive charge and Cl will get
slight negative charge, i.e.,
But IR radiation absorption is not possible in the
symmetric diatomic molecules like H2, O2, and N2 etc.,
because, symmetric diatomic molecules do not
possess electric dipole. , Therefore, IR radiation
absorption and IR spectrum is not possible in these
molecules.


H  Cl
dipole moment
OO
IR Active
llly H2O, NO
IR Inactive
No dipole moment
llly H2, Cl2
37
Infra RED Spectroscopy – Theory - Various types of molecular vibrations
bond length changes
bond angle changes
38
Infra RED Spectroscopy – Theory - Various types of molecular vibrations
Stretching: Rhythmical movement along the bond axis, which leads to the
increase or decrease of interatomic distance.
Symmetrical stretching
Anti-symmetrical stretching
39
Infra RED Spectroscopy – Theory - Various types of molecular vibrations
Bending:
Bending vibrations takes place when a three atom system is a
part of a molecule.
Types of Bending vibrations:
• Scissoring
• Wagging
• Rocking
• Twisting
40
Infra RED Spectroscopy – Theory - Various types of molecular vibrations
Scissoring: Two atoms attached to a central atom move away from and towards each other.
41
Infra RED Spectroscopy – Theory - Various types of molecular vibrations
Wagging: Vibrating group swings back and forth out of plane of molecule.
42
Infra RED Spectroscopy – Theory - Various types of molecular vibrations
Rocking: Vibrating group swings back and forth in the plane of molecule.
43
Infra RED Spectroscopy – Theory - Various types of molecular vibrations
Twisting: Vibrating group rotates about the chemical bond which is attached
to rest of molecule.
44
Infra RED Spectroscopy – Theory - Various types of molecular vibrations
bond length changes
bond angle changes
45
Infra RED Spectroscopy – Theory - Various types of molecular vibrations
bond length changes
bond angle changes
46
Infra RED Spectroscopy – Energy required for molecular vibrations
Energy required
Stretching
bond length changes
>
Bending
bond angle changes
Energy needed to stretch a spring is more than that needed to bend it so the stretching
absorption of a bond will appear at a higher frequency than the bending absorption of the
same bond.
Stretching > Bending > Wagging / Twisting
47
Infra RED Spectroscopy – Number of Fundamental vibrations
• A molecule containing n atoms has 3n degrees of freedom (translational, rotational, vibrational)
• In
Linear molecule with n number of atoms has:
3 degrees called the translational degrees of freedom (specify the centre of mass of
molecule representing the translational motion of molecule
2 degrees called the rotational degrees of freedom (specify the orientation of
molecule about its centre of mass, representing the rotational motion of molecule
3n – 5 degrees called the vibrational degrees of freedom (specify the relative
positions of the ‘n’ nuclei representing vibrational motion
• For Example: In CO2 the number of theoretical absorption bands could be (3x3-5 = 4) four.
Degrees of freedom
Molecule
Total Translational Rotational Vibrational
3n-5
HCl
6
3
2
1
CO2
9
3
2
4
48
Infra RED Spectroscopy – Number of Fundamental vibrations
• In
non-linear molecule with n number of atoms has:
3 degrees called the translational degrees of freedom (specify the centre of mass of
molecule representing the translational motion of molecule
3 degrees called the rotational degrees of freedom (specify the orientation of
molecule about its centre of mass, representing the rotational motion of molecule
3n – 6 degrees called the vibrational degrees of freedom (specify the relative
positions of the ‘n’ nuclei representing vibrational motion
• For Example: In CH4 the number of theoretical absorption bands could be (3x5-6 = 9) nine.
Degrees of freedom
Molecule Total
3n-6
Translational Rotational
Vibrational
H2O
9
3
3
3
NH3
12
3
3
6
CH4
15
3
3
9
49
Infra RED Spectroscopy – FUNDAMENTAL VIBRATION
 0  1
• The fundamental vibrations correspond in the quantum treatment to the first vibrational
transition from the zeroth vibrational level to the first,   
0
1
• At the room temperature most molecules are in the zeroth level.
4
3
2
1
Vibrational-rotational energy
levels for a diatomic molecule
0
=1
4
3
2
1
0
=0
50
Infra RED Spectroscopy – Overtones
• The term overtone is used in a general sense to apply to any multiple of a given fundamental
frequency.
 0   2 and  0  3
• The transitions from
are the first and second overtones of the
fundamental and require radiation of twice and thrice times its frequency.
• For example, for the carbonyl group C=O,
The fundamental vibration or the first vibrational transition,
i.e., for  0   1 the  C=O = 1700 cm
1
Therefore, the first overtone will be,
i.e., for  0   2 the 2 C=O = 3400 cm 1
In IRspectroscopy, most overtones are found in the near infrared region beyond 4000cm-1.
Overtone absorptions are much weaker than the fundamental absorptions.
51
Infra RED Spectroscopy – Harmonic molecular vibrations
• A bond A-B is stretched and released.
• The bond will revert back to its equilibrium position.
• The restoring force, k is proportional to the displacement, r, i.e., k = f. r, where f is force constant
•
The oscillation of the bond is designated as simple harmonic motion.
• For harmonic motion, a plot of potential energy of the system versus internuclear distance is a
parabola, which is symmetrical about the equilibrium distance, re.
• The energy of the system is given as E ; Where  = 0,1,2,…
52
Infra RED Spectroscopy – Anharmonic molecular vibrations
• For a real molecule the potential energy curve is not a perfect parabola.
• The vibrational energy levels are converging (coming closer) because of anharmonicity in the
vibration
53
Infra RED Spectroscopy – Absorptions due to harmonic & anharmonic molecular vibrations
A diatomic molecule makes a transition from one vibrational energy state to another by
absorbing or emitting electromagnetic radiation when the condition E=h is satisfied.
54
Infra RED Spectroscopy – Selection rules
Rule-1: For absorbing IR radiations a molecule should possess electric dipole (dipole moment) and
the absorption should causes change in electric dipole. i.e., the molecule should be IR
active. If no change in dipole moment accompanies the vibrations, then that mode is IR
inactive a vibration is taking
In other words, the vibrations without a centre of symmetry (i.e., Non-centrosymmetric),
are active in IR (but inactive in Raman spectroscopy)
For example: Vibrations in CO2
55
Infra RED Spectroscopy – Selection rules…
Vibration modes of carbon dioxide
Symmetrical Stretching vibrations
IR inactive
Asymmetrical Stretching vibrations
max = 2350cm-1
O
C
O
O
C
O
O
C
O
O
Bending vibrations
max = 667cm-1
C
O
Mode (a) is symmetric and results in no net displacement of the molecule's "center of charge",
and is therefore not associated with the absorption of IR radiation. [IR inactive]
Modes (b) and (c) do displace the "center of charge", creating a "dipole moment", and
therefore are modes that result from EM radiation absorption [IR Active]
Thus, two bands at 2350cm-1 and 667cm-1 pertaining to asymmetric stretching and bending
vibrations constitute the fundamental spectrum of CO2
56
Infra RED Spectroscopy – Selection rules…
IR spectrum of CO2
100
%T
80
60
O
O
C
C
O
O
C
O
O
40
20
0
4000
Asymmetrical Stretching vibration
max = 2350cm-1
3500
3000
2500
Bending vibrations
max = 667cm-1
2000
1500
1000
500
wavenumber/cm -1
57
Infra RED Spectroscopy – Selection rules
Rule-2: Only the transition  0  1 is allowed. The frequency corresponding to this transition is
called the fundamental frequency.
i.e., =1 transition only can occur.
The transitions from
 0   2 and  0  3 are not allowed due to anhormonicity.
For absorption = +1
For emission
= -1
58
Infra RED Spectroscopy – Fundamental vibrations…
But, in actual IR spectra the theoretical absorption bands (3n-5 or 3n-6) are not often obtained,
because,
• Fundamental vibrations falling outside the region (2.5-25).
• It is not possible to observe weak fundamental vibrations.
• Some fundamental vibrations are very close and so they overlap.
• Some additional bands known as combination bands appear.
• Hence the number of observed bands is different from theoretical bands.
59
Infra RED Spectroscopy – Fundamental vibrations…
Bands resulting from
1. Combination of vibrational frequencies (or)
2. Difference of vibrational frequencies (or)
3. By the interaction of overtone [(or combination band) with the fundamental vibration (Fermi resonance)]
1. Combination Bands
A number of weak absorptions occurs in the infrared spectra due to the sum of two or more
fundamental vibrational frequencies.
The combination modes arise from the anharmonicities of the oscillators which leads to an
interaction of the vibrational states in polyatomic molecules.
The resulting absorptions are weak compared to the fundamental vibrations and overtones.
60
Infra RED Spectroscopy – Fundamental vibrations…
2. Difference Modes
Some of the absorptions recorded in the infrared spectra correspond to the difference
between two vibrational frequencies.
In these cases, the molecule already existing in one excited vibrational state absorbs
enough additional radiant energy to raise it to another vibrational level in a different
vibrational mode.
The measured absorption is then the difference between the two.
3. Fundamental – Over tone interaction (Fermi Resonance)
When an overtone or combination band falls near a strong fundamental vibration, it causes
a decrease in the intensity of the fundamental vibration and a large increase in the intensity
of the overtone or combination vibration is known as Fermi resonance.
For example, the appearance of two moderately intense bands in the region 2830-2695 cm-1 in
aldehydes is due to the interaction between the aldehydic C-H stretch and the first overtone
of aldehydic C-H in-plane bending which appears near 1390 cm-1.
61
Infra RED Spectroscopy – Calculation of Vibrational frequencies
• The general region where a vibration will occur can be calculated using the Hooke’s law.
• According to Hooke’s law, Frequency of vibration is
• Directly proportional to the square root of the force constant (f) of the bond
• Inversely proportional to the square root of the reduced mass ()
i.e., Mathematically,



Where,   frequency in cm 1 (wavenumber)
1
f
2 c 
f  force constant in dyne cm1 (g sec2 )
c  velocity of light in cm sec1
  reduced mass
m1 - mass of atom 1 in g
m 2 - mass of atom 2 in g
Therefore,
62
Infra RED Spectroscopy – Calculation of Vibrational frequencies…
• Force constant may be linked to the stiffness, i.e., strength of the spring.
f
• The Hooke’s law equation corresponds to a simple model of two units coupled by a spring
in which the force constant is the restoring force provided by the spring.
• The general region in which the


1

2 2.998  1010 cm sec 1
12
C  1H
stretching frequency can be calculated using,
1 
 12
23
5.0 105 g sec 2 
+
 10 g
 6.023 6.023 
 12
  1

23

10
g
1023 g 

 
 6.023
  6.023


  3032 cm 1
Actual range for C- H stretching is 2850 – 3000 cm-1
63
Infra RED Spectroscopy – Intensity and position of IR absorption bands
• Intensity of a particular absorption depends upon the difference between the dipole moments
of the molecule in the ground state and excited state.
• The greater the difference in these dipole moments, the more intense the absorption.
• If no change in the dipole moment accompanies the vibrations, then that mode is IR inactive.
• In IR spectrum, intensity of peaks are assigned as follows,
• Base peak - the most intense peak with 100% relative intensity is called the base peak.
• Very strong peak – peaks with 80% intensity to that of the base peak
• Strong peak – peaks with 80% to 60% intensity to that of the base peak
• Medium peak – peaks with 60% to 50% intensity to that of the base peak
• Weak peak – peaks with 50% to 30% intensity to that of the base peak
• Very weak peak – peaks with <30% intensity to that of the base peak
64
Infra RED Spectroscopy – Factors affecting “frequency” of molecular vibrations
1. Mass of the atoms:
Light elements vibrate at higher
frequencies as compared to
heavier elements
Example-1:
H2
MM =2 g/mole
Heavier molecules will result
in slower movement and
result in lower frequencies
I2
MM =254 g/mole
The greater the mass - the lower the wavenumber
65
Infra RED Spectroscopy – Factors affecting “frequency” of molecular vibrations
1. Mass of the atoms….
Example-2:
C
H
H is lighter atom, absorbs at higher , 3000 cm-1
C
D
D is heavier atom, absorbs at lower , 2100 cm-1
66
Infra RED Spectroscopy – Factors affecting “frequency” of molecular vibrations
2. Bond Strength:
• Bond strength and the wavelength of absorption are proportional
• Thus, the stronger the bond the higher the wavelength of absorption
• Increasing number of bonds increases frequency of vibration
• Triple bonds being stiffer vibrate at higher frequencies as compared to double bonds
and double bonds vibrate at higher frequencies than single bonds
C C Stronger bond, absorbs at higher , 2250 cm-1
C
C Intermediate, absorbs at 1660 cm-1
C
C Weaker bond, absorbs at lower  , 1200 cm-1
2500-2000cm-1
Triple Bonds
CC, CN
2000-1500cm-1
Double Bonds
C=C, C=O, C=N
1500-400cm-1
Single Bonds
CC, CO, CN, CX
67
Infra RED Spectroscopy – Factors affecting “frequency” of molecular vibrations
3. Arrangement of various atoms in the molecule:
• Stretching frequencies of groups involving hydrogen (a light atom) such as C-H, N-H, O-H etc.,
all occur at comparatively high frequencies.
Bond
Frequency range
C-H (alkyl)
2850-2960cm-1
N-H (amine)
3300-3500cm-1
O-H (alcohol)
3600-3650cm-1
CC
2100-2250cm-1
C=C
1625-1685cm-1
68
Infra RED Spectroscopy – Factors affecting “frequency” of molecular vibrations
4. Force constant (Elasticity of the spring):
• Force constant is a measure of bond strength.
• Large force constants in general indicate stronger bonds
• Force constants for bending modes are much less than that of stretching modes.
• Force constant can be calculated if the fundamental vibrational frequency of a molecule is known.


1
f
2 c 
OR


1  f 
 
2 c   
1
2
2
Therefore,



f   2 c obs  




69
Infra RED Spectroscopy – Factors affecting “frequency” of molecular vibrations
4. Force constant (Elasticity of the spring):..
For example, for
1
H  Cl ,
35

  2.886  103 cm 1
Therefore, the force constant,
2



f   2 c obs  




2
 35amu 1.01amu 

10
1
3
1 
f   2  2.998  10 cm sec  2.886  10 cm  
 1.661 1027 kg.amu 1 
 35  1.01 amu


f  4.78 102 kg sec 1
70
Infra RED Spectroscopy – Factors affecting “frequency” of molecular vibrations
4. Force constant (Elasticity of the spring):…
• If H in C-H is replaced by there will be negligible change in force constant but appreciable
change in reduced mass. Therefore, frequency will be lower by a factor about
1
.
2
• C-H vibrations will occur at frequencies 1.3 to 1.4 times higher than the frequency of C- D vibration
Molecule
Force constant (f) x 105 in dynes/cm
HI
2.9
HBr
3.8
C-C
4.5
HCl
4.8
HF
8.8
C=C
9.6
C=O
12.1
NO
15.5
CC
15.6
CN
17.7
71
Infra RED Spectroscopy – Factors affecting “frequency” of molecular vibrations
4. Force constant (Elasticity of the spring):…
Molecule
Force constant (f) x 105 in dynes/cm
stretching frequency (cm-1)
C-C
4.5
1300-800
C=C
9.6
1640-1600
CC
15.6
2300-2100
72
Infra RED Spectroscopy – Factors affecting “frequency” of molecular vibrations
4. Force constant (Elasticity of the spring):…
• A stronger spring (bond) will cause the vibration in higher energy.
f
• A weaker spring (bond) will cause the vibration in lower energy.
f
73
Infra RED Spectroscopy – Factors affecting “frequency” of molecular vibrations
5. Conjugation:
Carbon-Carbon
Bond Stretching
• Stronger bonds absorb at higher frequencies:
– C-C
1200 cm-1
– C=C 1660 cm-1
– CC
2200 cm-1 (weak or absent if internal)
• Conjugation lowers the frequency:
– isolated C=C
1640-1680 cm-1
– conjugated C=C 1620-1640 cm-1
– aromatic C=C
approx. 1600 cm-1
74
Infra RED Spectroscopy – Factors affecting “frequency” of molecular vibrations
6. s character:
Carbon-Hydrogen
Stretching
Bonds with more s character absorb at a higher frequency.
– sp3 C-H, just below 3000 cm-1 (to the right)
– sp2 C-H, just above 3000 cm-1 (to the left)
– sp C-H, at 3300 cm-1
75
Infra RED Spectroscopy – Factors responsible for shifting the vibrational frequencies from their normal values
7. Coupled vibrations
• C – H group shows one stretching absorption frequency.
• In –CH2 group two absorptions occur which correspond to symmetric and asymmetric vibrations
• In such case asymmetric vibrations always occur at higher wave number compared to the
symmetric. These are called coupled vibrations since these vibrations occur at different
frequencies than that required for an isolated C-H stretching.
• Acid anhydrides show two C=O stretching absorptions between 1850-1800cm-1 and 17901745cm-1 with a difference of about 65cm-1. This is due to symmetric and asymmetric stretching
76
Infra RED Spectroscopy – Factors responsible for shifting the vibrational frequencies from their normal values
8. Fermi resonances
• When an overtone or combination band falls near a strong fundamental vibration, it causes a
decrease in the intensity of the fundamental vibration and a large increase in the intensity of the
overtone or combination vibration is known as Fermi resonance.
• The Fermi resonance, pushes the two bands apart and mixes their character so that each band
becomes partly fundamental and partly overtone in character. Thus, this type of resonance gives
to a pair of transitions of equal intensity.
• For example: n-butyl vinyl ether, the overtone of the fundamental vibration at 810cm-1 chances to
coincide with the band at 1640cm-1. The mixing of the two bands (fundamental & overtone) in
acordance with fermi resonance gives two bands of almost equal intensity at 1640cm-1 and
1630cm-1.
77
Infra RED Spectroscopy – Factors responsible for shifting the vibrational frequencies from their normal values
9. Electronic effects:
• Position of frequency shifts due to inductive effect, mesomeric effect, field effects etc. Under the
influence of these effects, the force constant or bond length changes and absorption frequency
shifts from normal value.
• Example-1: Alkyl group causes +I effect which results in the lengthening of the weakening of
the bond and hence the force constant is lowered and wave number decreases.
• (c=o) of Formaldehyde (HCHO) = 1750cm-1
• (c=o) of Acetaldehyde (CH3CHO) = 1745cm-1
• (c=o) of Acetone (CH3COCH3) = 1715cm-1
• Example-2: Introduction of an electronegative atom or group causes –I effect which results in the
increase in bond strength and force constant. Thus the wave number of absorption rises.
• (c=o) of Acetone (CH3COCH3) = 1715cm-1
• (c=o) of Chloroacetone (CH3COCH2Cl) = 1725cm-1
• (c=o) of Dichloroacetone (CH3COCHCl2) = 1740cm-1
• (c=o) of Tetrachloroacetone (CH2CHCOCHCl2) = 1750cm-1, 1778cm-1
78
Infra RED Spectroscopy – Factors responsible for shifting the vibrational frequencies from their normal values
10. Field effect:
• In ortho substituted compounds, inductive effects, mesomeric effect along with steric effect are
considered. In these compounds, the lone pairs of electrons on two atoms influence each other
through-space interactions and change the vibrational frequencies of both groups. This effect is
called field effect.
• Example: Ortho-Chloroacetophenone
• The nonbonding electrons of oxygen and chlorine undergo repulsion when they are close together
in the molecule.
• This cause a change in the state of hybridization of C=O group.
• Thus conjugation is diminished and absorption occurs at a higher wave number.
• In ortho substituted compounds, the cis form absorbs at higher frequency as compared to the
trans isomer.
Cl
79
Infra RED Spectroscopy – Factors responsible for shifting the vibrational frequencies from their normal values
11. Hydrogen bonding:
• Hydrogen bonding shifts absoption band to lower frequency region.
• The shift towards lower frequency depends upon the strength of the hydrogen bonding.
• The two types of hydrogen bonding can be readily distinguished in IR technique.
• Generally,
• Intermolecular hydrogen bonds give rise to broad bands
• Intramolecular hydrogen bonds gives sharp and well defined bands
• Intermolecular hydrogen bonds are concentration dependent. On dilution, the intensities of such
bands decrease as the intermolecular hydrogen bonds are broken causing a decrease in the
bonded O-H absorptions.
• But, Intramolecular hydrogen bonds remain unaffected on dilution and as a result the absorption
band also remains unaffected.
80
Infra RED Spectroscopy – Factors responsible for shifting the vibrational frequencies from their normal values
11. Hydrogen bonding:……..
• Example-1: In aliphatic alcohols, a sharp band appears at 3650cm-1 in dilute solutions due to free
O-H group while a broad band is noticed at 3350cm-1 due to hydrogen bonded O-H group.
• Alcohols are strongly hydrogen bonded in condensed phases.
• These are usually associated as dimers and polymers which result in the broadening of bands at
lower absorption frequencies.
• In vapour state or inert solvents, molecules exist in a free state and absorbs at 3650cm-1.
• Example-2: The spectrum of glycol in dilute CCl4 shows two bands at 3644cm-1 and 3612cm-1.
• The band at 3644cm-1 is due to free O-H and that at 3612cm-1 is due to intramolecular bonded
O-H.
• The absorption shift is small(32cm-1) for intra-molecular hydrogen bonding.
81
Infra RED Spectroscopy – Factors affecting intensity of molecular vibrations
12. Intensity of absorption depends on polarity of bond:
The more polar, the more intense the peak.
Example:
C= O very polar, intense peak
C  C nearly nonpolar, weak peak
82
Infra RED Spectroscopy - Instrumentation
An Infrared
Spectrometer
83
Infra RED Spectroscopy - Instrumentation
• The IR radiation from the radiation source is passed through a monochromator to select the
appropriate wavelength.
• Then the IR radiation is passed through the sample.
• The transmitted light is detected, amplified and IR spectrum is recorded.
• In IR spectroscopy the following components are used.
• IR radiation source: Nernst glower is used to generate IR radiation. Nernst glower is a
moulded rod made of mixture of rare earth metal oxides maintained at 1500C.
• Monochromator: Prism and grating made of metal halides like NaCl, KBr etc., are used as
monochromator to select appropriate wavelength.
• Detector: Thermocouple or bolometer is used as detector to detect the light and to convert
into electric signal.
• In IR spectroscopy gas, liquid or solution, solid substance can be used as samples and the
solvents like CCl4, CS2 and CHCl3 can be used as solvents.
84
Infra RED Spectroscopy - Applications
(i) Structure elucidation of organic compound
We know that, If IR radiations are passed through a molecule the different functional groups in
the molecule absorb IR radiations at their natural frequencies. This phenomenon is helpful in
elucidating the structure of organic compounds.
For example,
• If the IR spectrum of a organic molecule shows absorption band at 5.82 (wave number
range 1800cm-1 and 1650cm-1) then it is possible to identify that a carbonyl group should be
present in it.
• On the other hand if the IR spectrum contains no absorption band in between 5.4 to 6.3,
then it is certain that no carbonyl group is present in the compound.
• Likewise, if the presence of different functional groups in a compound is identified using the
IR spectrum then the structure of unknown compound can be deduced with the help of other
available data.
85
Infra RED Spectroscopy – Applications…
(ii) Structure identification
• The IR spectrum is useful in the identification of a newly synthesized compound.
• The IR spectrum of unknown compound can be compared with the absorption spectrum of
several known compounds in the literature.
• If the IR spectrum of unknown compound matches with a known compound then the
structures of both will also be similar. This method is called finger printing technique.
(iii) Identification of impurities
• If any extra absorption bands are recorded in the IR spectrum of a known compound then it
is certain that the compound is not pure.
• Therefore, the compound should be purified further to remove all the impurities.
• After purification, if the IR spectrum is recorded then there will not be any extra absorption
bands.
• Thus IR spectrum is useful in determining the purity of a compound. .
86
Infra RED Spectroscopy – Applications…
(iv) Study of reaction kinetics
• The rate of a reaction can be studied by recording IR spectrum of the reaction mixture at
definite intervals of time.
• From the IR spectrum disappearance of absorption bands recorded in the beginning (due to
the presence of reactants) and appearance of new absorption bands (due to the formation of
products) can be observed in the course of time.
• Thus the progress of organic reaction can be studied.
(v) To ascertain hydrogen bonding in a molecule
• In a sample with inter and intramolecular hydrogen bonding, if the dilution is increased and
the IR spectrum is recorded, the absorption band, due to intermolecular hydrogen bonding
disappears and the absorption band due to intramolecular hydrogen bonding remains
unchanged.
87
Infra RED Spectroscopy – IR Spectrum of some simple compounds
(i) Alkanes
•
•
Two C-H stretching absorption bands appear below 3000cm-1, for symmetric and
asymmetric vibrational frequencies.
Various C-H bending vibrations in alkane appear in the region 1495-1340cm-1
88
Infra RED Spectroscopy – IR Spectrum of some simple compounds…
(i) Alkanes…
89
Infra RED Spectroscopy – IR Spectrum of some simple compounds…
(ii) Alkenes
•
C-H stretching absorption bands appear in the region 3100cm-1 to 3000cm-1.
•
Conjugated double bond with aromatic ring shows C=C stretching near 1625cm-1.
•
For trans alkenes, C-H deformation comes around 970cm-1 and for corresponding cis
isomers, it appears about 700cm-1. This helps in distinguishing cis and trans isomers.
90
Infra RED Spectroscopy – IR Spectrum of some simple compounds…
(ii) Alkenes:…
91
Infra RED Spectroscopy – IR Spectrum of some simple compounds…
(iii) Alkynes:
•
In acetylene, a strong band for -CC-H appears at about 3300cm-1 and a weak CC
stretching appears at about 2200cm-1. C-H bending for acetylenes and mono substituted
acetylenes occurs at 650-610cm-1.
92
Infra RED Spectroscopy – IR Spectrum of some simple compounds…
(iii) Alkynes:…
93
Infra RED Spectroscopy – IR Spectrum of some simple compounds…
For C-C, C=C and CC groups:
94
Infra RED Spectroscopy – IR Spectrum of some simple compounds…
(iv) Cycloalkanes:
•
•
In Cycloalkanes C-H stretching frequency increases with increasing angle of strain in the ring.
For example.

The asymmetric CH2 stretching vibrations in cyclohexane occur at 2950cm-1.

For cyclopropane CH2 stretching vibration occur at 3100-2919cm-1.
With increasing strain in the ring, C-H bending also shows an increase. For example,

C-H bending in cyclopentane is 1455cm-1

For cyclohexane C-H bending is at 1442cm-1.
95
Infra RED Spectroscopy – IR Spectrum of some simple compounds…
(v) Aromatics Hydrocarbons:
•
Variable C-H stretching absorption occurs in the region 3050-3000cm-1
•
C=C at 1650-1450cm-1
•
C-H deformation vibrations at 900-700cm-1.
•
For aromatic compounds, the most characteristic C=C stretching bands are at 1600, 1580,
1500 and 1450 cm-1.
•
If there is no absorption in this region, it is a fair proof that the compound is not aromatic.
96
Infra RED Spectroscopy – IR Spectrum of some simple compounds…
(v) Aromatics Hydrocarbons:…..
•
Mono substituted benzene shows band at 710-690 (s) and 770-730 cm-1.
Toluene
Ar-H
(stretch)
C=C
(stretch) C—H
( bending)
Monosubstituted benzene
97
Infra RED Spectroscopy – IR Spectrum of some simple compounds…
(v) Aromatics Hydrocarbons:…..
•
Meta substituted benzene usually shows two bands, one at 710-690cm-1 and another at
800-750 cm-1.
•
Ortho and para substituted benzenes shows one band each at 770-735 cm-1 and at
840-800 cm-1 respectively.
98
Infra RED Spectroscopy – IR Spectrum of some simple compounds…
(vi) Halogen compounds:
•
In halogen compounds, the C-H stretching shifts to higher wave number due to the –I. effect
of the halogen atom.
•
C-X bonds show lower values of absorption frequencies as compared to C-H bond due to the
decreased force constant and increase in the reduced mass.
•
C-X stretching (X = CI, Br, I) absorption lies between 800-500cm-1 and C-F stretching
vibrations occur in the region 1400-1000cm-1.
•
The asymmetric C-H stretching vibrations of –CH3 group in CH3 -X occur above
3000cm-1 which is also the region for aromatic and unsaturated compounds.
99
Infra RED Spectroscopy – IR Spectrum of some simple compounds…
(vii) Alcohols:
•
The O-H stretching vibrations show a sharp band in the region 3700-3500cm-1, when a
spectrum of dilute solution of alcohol in CCI4 scanned.
•
If the spectrum is taken with increased concentration of alcoholic solution, the sharp band
disappears and a broad band appears at lower frequency region.
•
In polar solvents, O-H stretching appears at lower wave numbers due to the association of
alcohol molecules with solvent molecules.
100
Infra RED Spectroscopy – IR Spectrum of some simple compounds…
(vii) Alcohols:…
•
Primary alcohols show a strong band near 1050cm-1, and secondary alcohols near 1100 cm-1
in addition to another strong band at 1350 -1260 cm-1.
•
Tertiary alcohols can be distinguished due to the appearance of strong band at 1200cm-1 and
another at 1410-1310 cm-1 (due to C-O stretching and O-H stretching coupling).
•
In concentrated solution, or in the solid state, the O-H stretching absorption band becomes
broader and the absorption maximum depends upon concentration, nature of the solvent and
temperature.
•
In intermolecular hydrogen bonded molecules, absorption shifts are concentration dependent.
•
The O-H stretching absorption band appears at 3570-3450 cm-1 in compounds which show
intra-molecular hydrogen bonding. For such molecules, there is no abruption shift on diluting
the sample.
101
Infra RED Spectroscopy – IR Spectrum of some simple compounds…
(viii) Phenols:
•
In phenols, the frequency of the free O-H stretching lies near 3600 cm-1.
•
In addition to the band for O-H stretching phenols show characteristic strong C-O stretching
band near 1200cm-1 and another at 1410-1300 cm-1.
•
Phenols form intermolecular hydrogen bonds more readily than alcohols.
•
Hydroxyl group in the associated form absorbs at 3500-3300 cm-1.
•
Spectra of ortho substituted phenols show a free O-H band along with another band arising
from
intramolecularily bonded O-H group.
102
Infra RED Spectroscopy – IR Spectrum of some simple compounds…
(ix) Carbonyl Compounds:
•
The C=O in the carbonyl compounds shows a strong band at 1650-1950 cm-1.
•
The frequency of absorption due to carbonyl group depends mainly on the force constant
which depends upon inductive effect, conjugative effect, field effects and steric effects.
•
The position of absorption of C=O stretching for ,-unsaturated ketones occurs at a lower
frequency as compared to its saturated compound.
•
Aryl ketones show C=O stretching absorption at a lower wave number as compared to
aliphatic ketones.
•
The position of C=O stretching absorption also depends upon the ring size. The wave number
of absorption is raised with decrease ring size.
103
Infra RED Spectroscopy – IR Spectrum of some simple compounds…
(x) Aldehydes and Ketones:
•
The C=O bond of simple aldehydes and ketones absorb around 1750 cm-1.
•
Examples: HCHO 1750 cm-1; CH3CHO 1745 cm-1; CH3COCH3 1718 cm-1
104
Infra RED Spectroscopy – IR Spectrum of some simple compounds…
(x) Aldehydes and Ketones:
An Aldehyde IR Spectrum
•
C=O around 1750 cm-1.
105
Infra RED Spectroscopy – IR Spectrum of some simple compounds…
(x) Aldehydes and Ketones:
•
Aldehydes can be easily distinguished from ketones due to the presence of two weak C-H
stretching (asymmetric and symmetric) absorption bands, one near 2820 cm-1.
106
Infra RED Spectroscopy – IR Spectrum of some simple compounds…
(x) Aldehydes and Ketones:…
S.No.
Compound
C=O
I
CH3CHO
1745 cm-1
II
CH2=CH-CHO
1723 cm-1
III
CH2=C(CH3)-CHO
1702 cm-1
•
In II, conjugative effect dominates over –I effect and absorption occurs at low wave number.
•
In III, both conjugative and +I effect (due to CH3) operate in the same direction and help in
still lowering the wave number of absorption.
•
In cyclic ketones, C=O absorption increases, as the size of the ring decreases (ring strain
increases).
•
Examples: A rise in C=O with decrease in the ring size is due to change in the state of
hybridization in small rings. As the ring size decreases, the ring bonds become enriched in
p-component and C=O bond acquires greater s-charater.
•
Hence, force constant for C=O bond increases and also the wave number of absorption rises.
107
Infra RED Spectroscopy – IR Spectrum of some simple compounds…
(x) Aldehydes and Ketones:…
•
In a conformation in which halogen atom is in equatorial, the almost parallel dipole of C-X
and C=O bonds results in the rise of C=O absorption by 20cm-1 whereas no shift in C=O
absorption is caused when halogen is in the axial position.
•
Example The spectra of cis and trans 2-bromo-4-tert-butycyclohexanone.
•
The bulky tert-butyl group must be in the equatorial position.
•
When bromide atom is equatorial, it becomes cis and C=O absorption is raised by about
20cm-1.
•
When bromine atom is axial, then the configuration is trans which does not show any C=O
shift.
108
Infra RED Spectroscopy – IR Spectrum of some simple compounds…
(xi) Carboxylic acids:
•
This functional group shows two bands, one from C=O stretching and another for O-H
stretching. The absorption of O-H stretching appears as a broad band near 3000-2500 cm-1.
The C=O stretching absorption in aliphatic acid occurs at 1725-1700 cm-1.
•
An acid (-COOH) is formed from an aldehyde (-CHO) on replacing a hydrogen atom by an OH
group.
•
Due to the –I effect of OH group, C=O absorption for acid should occur at higher wave
number as compared to aldehydes. But it is not so. C=O absorption for acids is lowered
due to internal conjugation working in opposite direction].
•
,-unsaturated acids or aryl acids show carbonyl absorption at a lower wave number.
109
Infra RED Spectroscopy – IR Spectrum of some simple compounds…
(xi) Carboxylic acids:…
This O-H absorbs broadly, 2500-3500 cm-1,
due to strong hydrogen bonding.
110
Infra RED Spectroscopy – IR Spectrum of some simple compounds…
(xi) Carboxylic acids:…
•
Some of the acids such as acetic acid, benzoic acid etc, exist as dimers due to hydrogen
bonding.
•
Formation of bridge lowers the force constants and thus C=O and O-H absorption occur at
lower waver numbers.
•
As the hydrogen bonded structure is established by resonance, the O-H stretching occurs as a
broad band in the region 3000-2500 cm-1.
111
Infra RED Spectroscopy – IR Spectrum of some simple compounds…
(xi) Carboxylic acids:…
•
In cis-trans isomers of an acid, small differences in C=O absorption are observed.
•
But in the cases of cis-and trans-cinnamic acids and maleic acid-fumaric acid, C=O
absorption differences are larger.
•
Cis-cinnamic acid absorbs at a higher wavenumber.
•
It is due to steric effect caused by the bulky groups on the same side of the double bond.
•
Due to repulsive interactios, the C=O part of –COOH group goes out of the plane of the
double bond.
•
Thus conjugation diminishes and hence C=O absorption occurs at a higher wavenumber.
•
Similarly, maleic acid (cis) absorbs at 1705 cm-1 as compared to fumaric acid (trans) at
1690cm-1.
112
Infra RED Spectroscopy – IR Spectrum of some simple compounds…
(xii) Amino acids:…
•
IR spectra of amino acids are usually taken in the solid state.
•
In the aqueous solution or in the solid state, its presence can be detected by the absorption
of NH3+ and COO- groups.
•
Amino acids in the form of zwitter ions (NH3+ CH2COO-) do not show N-H stretching at
3200cm-1, but show a broad band between 3130 and 3030 cm-1 assigned to asymmetric
stretching of NH3+ group. In zwitter ions, two vibrational modes of the carboxylate ion are
readily identified between 1600-1400 cm-1.
•
The asymmetric vibrational band at 1600-1560 cm-1 is broad and strong.
113
Infra RED Spectroscopy - Interpreting Infrared Spectra
•
Check for signals near
–
–
–
3000 cm-1 - Alkanes vs alkenes vs alkynes
3400 cm-1 - OH vs NH vs NH2
1700 cm-1 - Aldehyde vs ketone vs ester vs acid vs amide
The principle goal will be identification of functional groups
114
Infra RED Spectroscopy - Quick Procedures for Infrared Analysis…
• It is important to remember that the absence of an absorption band can often provide more
information about the structure of a compound than the presence of a band.
• Be careful to avoid focusing on selected absorption bands and overlooking others.
• Use the examples linked to the table to see the profile and intensity of bands.
• Remember that the absence of a band may provide more information than the presence of an
absorption band.
115
Infra RED Spectroscopy - Quick Procedures for Infrared Analysis…
Look for absorption bands in decreasing order of importance:
1. the C-H absorption(s) between 3100 and 2850 cm-1. An absorption above 3000 cm-1
indicates C=C, either alkene or aromatic. Confirm the aromatic ring by finding peaks at 1600
and 1500 cm-1 and C-H out-of-plane bending to give substitution patterns below 900 cm-1.
Confirm alkenes with an absorption at 1640-1680 cm-1. C-H absorption between 3000 and
2850 cm-1 is due to aliphatic hydrogens.
2. the carbonyl (C=O) absorption between 1690-1760cm-1; this strong band indicates either an
aldehyde, ketone, carboxylic acid, ester, amide, anhydride or acyl halide. The an aldehyde
may be confirmed with C-H absorption from 2840 to 2720 cm-1.
3. the O-H or N-H absorption between 3200 and 3600 cm-1. This indicates either an alcohol, NH containing amine or amide, or carboxylic acid. For -NH2 a doublet will be observed.
116
Infra RED Spectroscopy - Quick Procedures for Infrared Analysis…
Look for absorption bands in decreasing order of importance:…
4. the C-O absorption between 1080 and 1300 cm-1. These peaks are normally rounded like the
O-H and N-H peak in 3. and are prominent. Carboxylic acids, esters, ethers, alcohols and
anhydrides all containing this peak.
5. the CC and C  N triple bond absorptions at 2100-2260 cm-1 are small but exposed.
6. a methyl group may be identified with C-H absorption at 1380 cm-1. This band is split into a
doublet for isopropyl(gem-dimethyl) groups.
7. structure of aromatic compounds may also be confirmed from the pattern of the weak
overtone and combination tone bands found from 2000 to 1600 cm-1.
117
Infra RED Spectroscopy - Comparison of IR Spectra
IR spectra, an IR spectra comparison tool and spectral problems are available at:
http://www.chem.ucla.edu/~webspectra
118
Infra RED Spectroscopy – References
1.
Spectroscopy of Organic Compounds, by P.S. Kalsi, 2nd Edition, (1996).
2.
Practical guide to Interpretive Near-Infrared Spectroscopy, by Jerry Workman &
Lois Weyer, CRC Press.
3.
Organic Spectroscopy: Principles and Applications, by Jag Mohan, 2nd Edition,
(2009).
4.
Spectrometric Identification of Organic Compounds, by Silverstein, Bassler,
Morrill, 5th Edition, (1991).
5.
Introduction to Spectroscopy, by Pavia, Lampman, Kriz, 3rd Edition, (2001).
6.
Applied Chemistry, by K. Sivakumar, Ist Edition, (2009).
7.
Instrumental Methods of Chemical Analysis, by Gurdeep.R. Chatwal, Sham
Anand, Ist Edition, (1999).
8.
www.spectroscopyNOW.com
119
120
Good Luck!
Dr. K. SIVAKUMAR
Department of Chemistry
SCSVMV University
[email protected]
121