Infrared spectroscopy is a technique that uses infrared light to analyze chemical bonding and structure. It works by measuring the frequencies at which molecules vibrate and absorb infrared radiation. Modern infrared instruments use a Fourier transform method with an interferometer to produce an infrared spectrum that acts as a molecular "fingerprint". Infrared spectroscopy is useful for identifying unknown materials, determining molecular structure of organic and inorganic compounds, and studying molecular interactions.

1. Infrared Spectroscopy
Prepared by
Dr. P.Malairajan, M.Pharm, Ph.D
Professor and Head

2. 12/15/2019 2

3. Spectroscopy is the study of the interaction of matter with the
electromagnetic spectrum
1. Electromagnetic radiation displays the properties of both particles and
waves
2. The particle component is called a photon
3. The energy (E) component of a photon is proportional to the frequency.
Where h is Planck’s constant and n is the frequency in Hertz (cycles per
second)
E = hn
4. The term “photon” is implied to mean a small, massless particle that
contains a small wave-packet of EM radiation/light – we will use this
terminology in the course
Introduction

4. 5. Because the speed of light, c, is constant, the frequency, n, (number
of cycles of the wave per second) can complete in the same time, must
be inversely proportional to how long the oscillation is, or wavelength:
6. Amplitude, A, describes the wave height, or strength of the oscillation
7. Because the atomic particles in matter also exhibit wave and particle
properties (though opposite in how much) EM radiation can interact
with matter in two ways:
• Collision – particle-to-particle – energy is lost as heat and
movement
• Coupling – the wave property of the radiation matches the wave
property of the particle and “couple” to the next higher quantum
mechanical energy level
n =
c = 3 x 1010 cm/s
___
l
c
E = hn =
___
l
hc
Introduction

5. 8. The entire electromagnetic spectrum is used by chemists:
UVX-rays IRg-rays RadioMicrowave
Energy (kcal/mol)
300-30 300-30 ~10-4> 300 ~10-6
Visible
Frequency, n in Hz
~1015 ~1013 ~1010 ~105~1017~1019
Wavelength, l
10 nm 1000 nm 0.01 cm 100 m~0.01 nm~.0001 nm
nuclear
excitation
(PET)
core
electron
excitation
(X-ray
cryst.)
electronic
excitation
(p to p*)
molecular
vibration
molecular
rotation
Nuclear Magnetic
Resonance NMR
(MRI)
Introduction

6. C. The IR Spectroscopic Process
1. The quantum mechanical energy levels observed in IR
spectroscopy are those of molecular vibration
2. We perceive this vibration as heat
3. When we say a covalent bond between two atoms is of a
certain length, we are citing an average because the bond
behaves as if it were a vibrating spring connecting the two atoms
4. For a simple diatomic molecule, this model is easy to visualize:
Introduction

7. C. The IR Spectroscopic Process
5. There are two types of bond vibration:
• Stretch – Vibration or oscillation along the line of the bond
• Bend – Vibration or oscillation not along the line of the bond
H
H
C
H
H
C
scissor
asymmetric
H
H
CC
H
H
CC
H
H
CC
H
H
CC
symmetric
rock twist wag
in plane out of plane
Introduction

8. C. The IR Spectroscopic Process
6. As a covalent bond oscillates – due to the oscillation of the
dipole of the molecule – a varying electromagnetic field is
produced
7. The greater the dipole moment change through the vibration,
the more intense the EM field that is generated
Introduction

9. C. The IR Spectroscopic Process
8. When a wave of infrared light encounters this oscillating EM field
generated by the oscillating dipole of the same frequency, the two
waves couple, and IR light is absorbed
9. The coupled wave now vibrates with twice the amplitude
IR beam from spectrometer
EM oscillating wave
from bond vibration
“coupled” wave
Introduction

10. Sample
Compartment
IR Source Detector
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11. • Infrared spectroscopy is an instrumental
method of analysis that can be used to identify
and quantify samples ranging from
pharmaceuticals to diesel emissions.
 wavelength is measured in "wavenumbers”
 wavenumber = 1 / wavelength in centimeters.
• if wavelength is 2.5 µ= 1 / (2.5x10-4 cm)= 4000 cm-1
• wavelength 15 µ corresponds to 667 cm-1
• 1 µ= 10-4 cm
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12. • Mid IR most useful (chemical fingerprinting)
• These absorptions represent vibrational and
rotational transitions
• Change in dipole moment required during vibration
for IR absorption to occur
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Regions of wavelength range
IR wavelength Wave number
Near IR 0.8-2.5 µ 12,500-4000 cm–1
Mid IR 2.5-15 µ 4000-667 cm–1
Far IR 15-200 µ 667-50 cm–1

13. Typical Mid-IR Spectrum
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14. 12/15/2019 14

15.  Modern IR is Fourier Transform instruments.
 A Michelson interferometer produce interference
between two beams of light and was invented by
Albert Abraham Michelson.
 The Michelson interferometer produces interference
fringes by splitting a beam of monochromatic light,
such that one beam hits a fixed mirror and the other
hits a movable mirror. When the reflected beams are
combined, an interference pattern is formed.
 In all transmission experiments radiation from a
source is directed through the sample to a detector.
 The measurement of the type and amount of light
transmitted by the sample gives information about
the structure of the molecules comprising the sample.12/15/2019 15

16. Infrared
Source
Detector
Sample
Compartment
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17. • In the IR region of the electromagnetic
spectrum, the absorption of radiation by a
sample is due to changes in the
vibrational energy states of a molecule.
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18. Types of
Molecular
Vibrations
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19. Vibrational Modes
 Linear molecules: 3N – 5 modes
 Nonlinear molecules: 3N – 6 modes
 Polyatomic molecules may exhibit coupling which
will alter predicted frequencies:
stretching-stretching
bending-bending
stretching-bending
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Note: strong coupling requires
interaction with a common atom

20. Carbon Dioxide
Stretching :
Bending (scissoring, degenerate):
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2330 cm–1
667 cm–1667 cm–1

21. Water
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22. Quantitative Aspects
• Frequency of molecular vibration, n (s–1) depends
on mass of atoms and strength of bond:
• The force constant, k, is about 500 N/m for a
typical single bond
• The reduced mass, m (kg), is defined
12/15/2019 22
mp
n
k
2
1

21
21
mm
mm

m
The pattern of absorption as a function of wavelength is called an IR
spectrum.

23. Theory of infra red absorption
 IR radiation does not have enough energy to
induce electronic transitions as seen with UV.
 Absorption of IR is restricted to compounds with
small energy differences in the possible
vibrational and rotational states.
 For a molecule to absorb IR, the vibrations or
rotations within a molecule must cause a net
change in the dipole moment of the molecule.
12/15/2019 23

24. Molecular rotations
 Rotational transitions are of little use to the
spectroscopist.
 Rotational levels are quantized, and absorption of
IR by gases yields line spectra.
 However, in liquids or solids, these lines broaden
into a continuum due to molecular collisions and
other interactions.
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25. Examples of spectra
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26. Examples of spectra
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27. Percentage transmittance
 A percentage transmittance of 100 would mean that
all of that frequency passed straight through the
compound without any being absorbed.
 In practice, that never happens - there is always
some small loss, giving a transmittance of perhaps
95% as the best you can achieve.
 A transmittance of only 5% would mean that nearly
all of that particular frequency is absorbed by the
compound. A very high absorption of this sort tells
you important things about the bonds in the
compound.
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28. Scheme of spectrometer
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29. Instrumentation
 Source
 Wavelength selector
 Sample holder
 Detector
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30. Sources
 Tungsten lamp
 Nernst glower
 Globar
 Nichrome coil
 Mercury arc lamp
 Carbon dioxide laser
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31. Sources
Tungsten lamp
Near IR only
Nernst glower
Globar
Nichrome coil
Mercury arc lamp
Carbon dioxide laser
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32. Sources
Tungsten lamp
Nernst glower
– A 2-5 cm rod, 1-3 mm in diameter, composed of oxides
of Zr, Y, Th
– Electrically heated to 1200-2000K, emits mid-IR
– current-limiting required
Globar
Nichrome coil
Mercury arc lamp
Carbon dioxide laser
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33. Sources
• Tungsten lamp
• Nernst glower
• Globar
– Silicon carbide rod, 6 x 50 mm
– Electrically heated to 1600K, emits mid-IR; better than
Nernst glower at <5 mm
• Nichrome coil
• Mercury arc lamp
• Carbon dioxide laser
12/15/2019 33

34. Sources
• Tungsten lamp
• Nernst glower
• Globar
• Nichrome coil
– Electrically heated to 1100K, emits mid-IR
• Mercury arc lamp
• Carbon dioxide laser
12/15/2019 34

35. Sources
• Tungsten lamp
• Nernst glower
• Globar
• Nichrome coil
• Mercury arc lamp
– High pressure (> 1 atm), emits far IR
• Carbon dioxide laser
12/15/2019 35

36. Sources
• Tungsten lamp
• Nernst glower
• Globar
• Nichrome coil
• Mercury arc lamp
• Carbon dioxide laser
– Many discrete lines from 9-11 mm
– Very intense
12/15/2019 36

37. Wavelength Selection
 Interference filters, wedges
 Prisms
 Quartz (0.8-3 mm) near IR
 LiF (1-5 mm) near IR
 NaCl (2.5-20 mm) mid-IR
 KBr, CsBr (15-40 mm) far-IR
 Reflection gratings (Al coated)
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38. Conditions of work
 Rigorous
 Base line
 Moisture
 CO2
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39. • To obtain an IR spectrum, the sample must be
placed in a “container” or cell that is
transparent in the IR region of the spectrum.
• Sodium chloride or salt plates are a common
means of placing the sample in the light beam
of the instrument.
12/15/2019 39

40. Sample Handling
• Gases
– 10 cm to 120 cm path lengths (may utilize multiple
reflection)
• Liquids—thin (0.1 mm) layers used
– Water or ROH are no-no’s (Why?)
– 10% in CCl4 (4000-1333 cm–1)
– 10% in CS2 (1333-650 cm –1)
– CHCl3, CH3CN, acetone for more polar substances
– neat liquids
• Evaporated Films
12/15/2019 40

41. Liquid IR Cell
12/15/2019 41

42. A satisfactory spectrum has well
defined peaks-but not so intense as
to cause flattening on the bottom of
the peaks.
Major peaks can be labeled using
the peak function of the software
12/15/2019 42

43. Well-defined
peaks are
labeled with the
Wavenumbers
of the
Absorption
Maxima.
12/15/2019 43
The spectrum can then be printed using the print
function of the software.

44. 12/15/2019 44

45. Sample of a
printout of
an IR
spectrum.
12/15/2019 45
A sample of a printout of an IR spectrum.

46. CYCLOHEXANE
Solvent
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The salt plates are cleaned by rinsing into a waste
container with a suitable organic solvent-commonly
cyclohexane.
NEVER WATER!

47. Detectors
Thermopiles
Thermistors
Photoconductors
Pyroelectric detectors
Golay detector
12/15/2019 47

48. Thermopiles
 Thermocouples
 Typical junctions
include Pt-Ag, Sb-Bi
 Sensitive to
temperatures changes
of 1 mK
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49. Thermistors and Photoconductors
o Thermistors
Temperature-sensitive resistors
Typically have very large R/T values
o Photoconductors
Temperature-sensitive resistors
PbS is typical
Near IR only
12/15/2019 49

50. Pyroelectric Detectors
Temperature sensitive capacitors
Triglycine sulfate (TGS)
Lithium tantalate (LiTaO3)
Lithium niobate (LiNbO3)
Materials have large (dipole)/T
Response times of 1 ms or less (fast for IR
detectors)
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51. Golay Detector
 Essentially a Xe gas thermometer
 Expensive, not better than other detectors in
near to mid IR
 Very useful in far IR
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52. Dispersive IR Spectrophotometer
 Monochromator
after sample
 Low frequency
chopper (10 min–1)
 Works on nulling
principle: reference
beam attenuated to
match sample beam
12/15/2019 52

53. Michelson Interferometer
12/15/2019 53
n






c
v
f m2

54. 12/15/2019 54
The heart of the FTIR is a Michelson interferometer
The mirror moves at a fixed rate. Its position is determined
accurately by counting the interference fringes of a collocated
Helium-Neon laser.
The Michelson interferometer splits a beam of radiation into two
paths having different lengths, and then recombines them.
A detector measures the intensity variations of the exit beam as
a function of path difference.
A monochromatic source would show a simple sine wave of
intensity at the detector due to constructive and destructive
interference as the path length changes

55. Infrared Group Analysis
A. General
1. The primary use of the IR is to detect functional groups
Because the IR looks at the interaction of the EM spectrum
with actual bonds, it provides a unique qualitative probe into
the functionality of a molecule, as functional groups are
merely different configurations of different types of bonds
2. Since most “types” of bonds in covalent molecules have
roughly the same energy, i.e., C=C and C=O bonds, C-H
and N-H bonds they show up in similar regions of the IR
spectrum
3. Remember all organic functional groups are made of
multiple bonds and therefore show up as multiple IR bands
(peaks)

56. IR Spectrum
 No two molecules will give exactly the same IR spectrum
(except enantiomers)
 Simple stretching: 1600-3500 cm-1
 Complex vibrations: 400-1400 cm-1, called the “fingerprint
region” 56
Baseline
Absorbance/
Peak

57. 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
57

58. 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
58

59. 1. Alkanes – combination of C-C and C-H bonds
• C-C stretches and bends 1360-1470 cm-1
• CH2-CH2 bond 1450-1470 cm-1
• CH2-CH3 bond 1360-1390 cm-1
• sp3 C-H between 2800-3000 cm-1
Octane
(w – s) (m)

60. An Alkane IR Spectrum
60

61. 2. Alkenes – addition of the C=C and vinyl C-H bonds
• C=C stretch at 1620-1680 cm-1 weaker as
substitution increases
• vinyl C-H stretch occurs at 3000-3100 cm-1
• The difference between alkane, alkene or alkyne
C-H is important! If the band is slightly above 3000
it is vinyl sp2 C-H or alkynyl sp C-H if it is below it
is alkyl sp3 C-H
1-Octene
(w – m)
(w – m)

62. An Alkene IR Spectrum
62

63. 3. Alkynes – addition of the C=C and vinyl C-H
bonds
• C≡C stretch 2100-2260 cm-1; strength depends
on asymmetry of bond, strongest for terminal
alkynes, weakest for symmetrical internal
alkynes
• C-H for terminal alkynes occurs at 3200-3300
cm-1
• Internal alkynes ( R-C≡C-R ) would not have this
band
1-Octyne
(m – s)
(w-m)

64. An Alkyne IR Spectrum
64

65. 4. Aromatics
• Due to the delocalization of e- in the ring, C-C bond
order is 1.5, the stretching frequency for these
bonds is slightly lower in energy than normal C=C
• These show up as a pair of sharp bands, 1500 &
1600 cm-1, (lower frequency band is stronger)
• C-H bonds off the ring show up similar to vinyl C-H
at 3000-3100 cm-1
Ethyl benzene
(w – m) (w – m)

66. 4. Aromatics
• If the region between 1667-2000 cm-1 (w) is free of interference (C=O
stretching frequency is in this region) a weak grouping of peaks is
observed for aromatic systems
• Analysis of this region, called the overtone of bending region, can lead
to a determination of the substitution pattern on the aromatic ring
Monosubstituted
1,2 disubstituted (ortho or o-)
1,2 disubstituted (meta or m-)
1,4 disubstituted (para or p-)
G
G
G
G
G
G
G

67. 5. Unsaturated Systems – substitution patterns
• The substitution of aromatics and alkenes can also be discerned
through the out-of-plane bending vibration region
• However, other peaks often are apparent in this region. These
peaks should only be used for reinforcement of what is known or
for hypothesizing as to the functional pattern.
R
C
H
C
R
C
H
CH2
R
C
H
C
R
C
R
CH2
R
C
R
C
R
H
R
H
R
H
985-997
905-915
cm-1
960-980
665-730
885-895
790-840
R
R
R
R
R
RR
cm-1
730-770
690-710
735-770
860-900
750-810
680-725
800-860

68. 6. Ethers – addition of the C-O-C asymmetric
band and vinyl C-H bonds
• Show a strong band for the antisymmetric C-
O-C stretch at 1050-1150 cm-1
• Otherwise, dominated by the hydrocarbon
component of the rest of the molecule
Diisopropyl ether
(s)

69. 7. Alcohols
• Strong, broad O-H stretch from 3200-3400 cm-1
• Like ethers, C-O stretch from 1050-1260 cm-1
• Band position changes depending on the alcohols
substitution: 1° 1075-1000; 2° 1075-1150; 3°
1100-1200; phenol 1180-1260
• The shape is due to the presence of hydrogen
bonding
1-butanol
(m– s)
br
(s)

70. O-H and N-H Stretching
 Both of these occur around 3300 cm-1, but they look
different
– Alcohol O-H, broad with rounded tip
– Secondary amine (R2NH), broad with one sharp
spike
– Primary amine (RNH2), broad with two sharp
spikes
– No signal for a tertiary amine (R3N)
70

71. An Alcohol IR Spectrum
71

72. 8. Amines - Primary
• Shows the –N-H stretch for NH2 as a doublet
between 3200-3500 cm-1 (symmetric and anti-
symmetric modes)
• -NH2 has deformation band from 1590-1650
cm-1
• Additionally there is a “wag” band at 780-820
cm-1 that is not diagnostic
2-aminopentane
(w) (w)

73. An Amine IR Spectrum
73

74. 9. Amines – Secondary
• N-H band for R2N-H occurs at 3200-3500
cm-1 as a single sharp peak weaker than
–O-H
• Tertiary amines (R3N) have no N-H bond
and will not have a band in this region
pyrrolidine
(w – m)

75. Pause and Review
• Inspect the bonds to H region (2700 – 4000 cm-1)
• Peaks from 2850-3000 are simply sp3 C-H in most organic
molecules
• Above 3000 cm-1 Learn shapes, not wavenumbers!:
Broad U-shape peak
-O—H bond
V-shape peak
-N—H bond for 2o
amine (R2N—H)
Sharp spike
-C≡C—H bond
W-shape peak
-N—H bond for 1o
amine (RNH2)
3000 cm-1
Small peak shouldered
just above 3000 cm-1
C=C—H or Ph—H

76. Carbonyl Stretching
 The C=O bond of simple ketones, aldehydes, and carboxylic
acids absorb around 1710 cm-1
 Usually, it’s the strongest IR signal
 Carboxylic acids will have O-H also
 Aldehydes have two C-H signals around 2700 and 2800 cm-1
76

77. 10.Aldehydes
• C=O (carbonyl) stretch from 1720-1740 cm-1
• Band is sensitive to conjugation, as are all
carbonyls (upcoming slide)
• A highly unique sp2 C-H stretch appears as a
doublet, 2720 & 2820 cm-1 called a “Fermi
doublet”
Cyclohexyl carboxaldehyde
(w-m)
(s)

78. An Aldehyde IR Spectrum
78

79. 11.Ketones
• Simplest of the carbonyl compounds as
far as IR spectrum – carbonyl only
• C=O stretch occurs at 1705-1725 cm-1
3-methyl-2-pentanone
(s)

80. A Ketone IR Spectrum
80

81. 12.Esters
• C=O stretch at 1735-1750 cm-1
• Strong band for C-O at a higher frequency
than ethers or alcohols at 1150-1250 cm-1
Ethyl pivalate
(s)
(s)

82. 13.Carboxylic Acids:
• Gives the messiest of IR spectra
• C=O band occurs between 1700-1725 cm-1
• The highly dissociated O-H bond has a broad band from
2400-3500 cm-1 covering up to half the IR spectrum in
some cases
4-phenylbutyric acid
(w – m)
br
(s) (s)

83. O-H Stretch of a Carboxylic Acid
This O-H absorbs broadly, 2500-3500 cm-1,
due to strong hydrogen bonding
83

84. Variations in C=O Absorption
 Conjugation of C=O with C=C lowers the stretching frequency to
~1680 cm-1
 The C=O group of an amide absorbs at an even lower frequency,
1640-1680 cm-1
 The C=O of an ester absorbs at a higher frequency, ~1730-1740
cm-1
 Carbonyl groups in small rings (5 C’s or less) absorb at an even
higher frequency
84

85. 14.Acid anhydrides
• Coupling of the anhydride though the ether
oxygen splits the carbonyl band into two with a
separation of 70 cm-1
• Bands are at 1740-1770 cm-1 and 1810-1840 cm-1
• Mixed mode C-O stretch at 1000-1100 cm-1
Propionic anhydride
O
O O
(s) (s)

86. 15.Acid halides
• Clefted band at 1770-1820 cm-1 for C=O
• Bonds to halogens, due to their size (see
Hooke’s Law derivation) occur at low
frequencies, only Cl is light enough to have
a band on IR, C-Cl is at 600-800 cm-1
Propionyl chloride
Cl
O
(s)
(s)

87. 16.Amides
• Display features of amines and carbonyl
compounds
• C=O stretch at 1640-1680 cm-1
• If the amide is primary (-NH2) the N-H stretch
occurs from 3200-3500 cm-1 as a doublet
• If the amide is secondary (-NHR) the N-H stretch
occurs at 3200-3500 cm-1 as a sharp singlet
pivalamide
NH2
O
(m – s) (s)

88. An Amide IR Spectrum
88

89. Carbon - Nitrogen Stretching
 C - N absorbs around 1200 cm-1
 C = N absorbs around 1660 cm-1 and is much stronger than
the C = C absorption in the same region
 C  N absorbs strongly just above 2200 cm-1. The alkyne C 
C signal is much weaker and is just below 2200 cm-1
89

90. 17.Nitro group (-NO2)
• Proper Lewis structure gives a bond order of
1.5 from nitrogen to each oxygen
• Two bands are seen (symmetric and
asymmetric) at 1300-1380 cm-1 and 1500-
1570 cm-1
• This group is a strong resonance withdrawing
group and is itself vulnerable to resonance
effects
2-nitropropane
N
O
O
(s) (s)

91. 18. Nitriles (the cyano- or –C≡N group)
• Principle group is the carbon nitrogen
triple bond at 2100-2280 cm-1
• This peak is usually much more
intense than that of the alkyne due to
the electronegativity difference
between carbon and nitrogen
propionitrile
N
C
(s)

92. A Nitrile IR Spectrum
92

93. Effects on IR bands
1. Conjugation – by resonance, conjugation lowers the energy of a double or triple
bond. The effect of this is readily observed in the IR spectrum:
• Conjugation will lower the observed IR band for a carbonyl from 20-40 cm-1
provided conjugation gives a strong resonance contributor
• Inductive effects are usually small, unless coupled with a resonance
contributor (note –CH3 and –Cl above)
O
O
1684 cm-1
1715 cm-1
C=O C=O
C
H3C
O
X X = NH2 CH3 Cl NO2
1677 1687 1692 1700 cm-1
H2N C CH3
O
Strong resonance contributor
vs.
N
O
O
C
CH3
O
Poor resonance contributor
(cannot resonate with C=O)

94. Effects on IR bands
2. Steric effects – usually not important in IR spectroscopy, unless they reduce
the strength of a bond (usually p) by interfering with proper orbital overlap:
• Here the methyl group in the structure at the right causes the carbonyl
group to be slightly out of plane, interfering with resonance
3. Strain effects – changes in bond angle forced by the constraints of a ring will
cause a slight change in hybridization, and therefore, bond strength
• As bond angle decreases, carbon becomes more electronegative, as well
as less sp2 hybridized (bond angle < 120°)
O
C=O: 1686 cm-1
O
C=O: 1693 cm-1
CH3
O O O O O
1815 cm-1
1775 cm-1
1750 cm-1
1715 cm-1
1705 cm-1

95. Effects on IR bands
4. Hydrogen bonding
• Hydrogen bonding causes a broadening in the band due to the creation of
a continuum of bond energies associated with it
• In the solution phase these effects are readily apparent; in the gas phase
where these effects disappear or in lieu of steric effects, the band appears
as sharp as all other IR bands:
Gas phase spectrum of
1-butanol
Steric hindrance to H-bonding
in a di-tert-butylphenol
• H-bonding can interact with other functional groups to lower frequencies
OH
C=O; 1701 cm-1
OO
H

96. Summary of IR Absorptions
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97. Strengths and Limitations
 IR alone cannot determine a structure
 Some signals may be ambiguous
 The functional group is usually indicated
 The absence of a signal is definite proof that the
functional group is absent
 Correspondence with a known sample’s IR spectrum
confirms the identity of the compound
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98. Conclusions
 IR identifies the components of a sample (liquid, solid or gas).
 Infrared (IR) spectrometers measure the interaction of IR
radiation with samples.
 The FTIR spectrometer measures the frequencies at which the
samples absorb the radiation, and the intensities of the
absorptions.
 Intensity and frequency of samples absorption are depicted in a
two-dimensional plot called a spectrum.
 Intensity is generally reported in terms of absorbance - the
amount of light absorbed by a sample, or percent transmittance
– i.e. the amount of light, which passes through it.
 What makes up an unknown sample, and how much of each
component is present in that sample, can be valuable
information supplied by this technique. Its many applications
include research and development of new products.
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99. Sources of informations
1. Y.R.Sharma, Elementary Organic Spectroscopy, 5th
Edition, S.Chand &Company Pvt.Ltd, New Delhi, 2013,
74-147
2. http://www.cem.msu.edu/~parrill/AIRS/
3. http://www.wpi.edu/Academics/Depts/Chemistry/Cou
rses/CH2670/infrared.html
4. http://www.chem.ucla.edu/~webspectra/irintro.html
5. http://www.spectro.com/pages/e/index.ht
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