Applications of Infra Red Spectroscopy

International Journal of Trend in Scientific Research and Development (IJTSRD)
Volume 6 Issue 4, May-June 2022 Available Online: www.ijtsrd.com e-ISSN: 2456 – 6470
@ IJTSRD | Unique Paper ID – IJTSRD50139 | Volume – 6 | Issue – 4 | May-June 2022 Page 535
Applications of Infra-Red Spectroscopy
Ganga Shy Meena
Assistant Professor, Department of Chemistry, Government College, Sawai Madhopur, Rajasthan, India
ABSTRACT
IR spectroscopy (which is short for infrared spectroscopy) deals with
the infrared region of the electromagnetic spectrum, i.e. light having
a longer wavelength and a lower frequency than visible light. Infrared
Spectroscopy generally refers to the analysis of the interaction of a
molecule with infrared light. The IR spectroscopy concept can
generally be analyzed in three ways: by measuring reflection,
emission, and absorption. The major use of infrared spectroscopy is
to determine the functional groups of molecules, relevant to both
organic and inorganic chemistry.
KEYWORDS: IR spectroscopy, electromagnetic, alkanes,
applications, reflection, emission, absorption, functional, structure,
range
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INTRODUCTION
Infra-red spectrum of a compound provides more
information than is normally available from the
electronic spectra. In this technique, almost all groups
absorb characteristically within a definite range. The
shift in the position of absorption for a particular
group may change (within the range) with the
changes in the structure of the molecule. [1,2]
IJTSRD50139

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1. Alkane
C-H stretching is most characteristic of alkanes, C-H
bending is also sighificant C-H stretching appear in
the range of 2960-2850 Cm-1
(m,s).
Methyl group shows two distinct bands at 2962 Cm-1
and 1872 Cm-1
for asymmetric and symmetric
stretching mode respectively. methyelene group have
asymmetric stretching at 2926 Cm-1
and symmetric stretching at 2853 Cm-1
.The bending
vibration of methyl group and methyelne group occur
at 1380Cm-1
and 1465 Cm-1
The band resulting from methyelene rocking vibration
appears at 720 Cm-1
.
2. Alkene
C=C Hstr. - 3100-3000Cm-1
C=C stretching vibration show medium absorption
band at 1680-1460Cm-1
absorption frequency of C=C
is reduced by about 30Cm-1
due to conjugation.
R-CH=CH2 C6H5-CH=CH2 =CH2
1640 1625 (all in Cm-1
)
Olefinic C-H stretching vibration band occurs around
3080 Cm-1
, which is also the region of aromatic C-H
stretching. The Characteristic of olefins is out of
Plane C-H bending at 1000-650Cm1
.
3. Alkynes
Alkynes have two stretching modes:
C≡C stretch at 2260-2100 Cm-1
.
≡ C-H stretch at 3300Cm-1
.
C-H bending vibration of alkyne occurs at 700-610
Cm-1
In internal alkyne (R-C≡C-R) C≡C stretch may
be very weak or absent due to small or no change in
dipole moment. [3,4]
4. Aromastic hydrocarbon
A. Aromatic C-H stretch occur at 3050-3000Cm-1
B. Overtone appears at 2000-1650Cm-1
C. C-C ring stretch occur at 1600, 1580, 1500, 1450
Cm-1
Vibration frequency is lowered due to
conjugation.
D. Out of plance C-H band at below 900Cm-1
. This
spectra is most infomative.
5. Alcohol and phenol
O-H stretching & C-O stretching are characteristic
stretching. If OH is free then sharp absorption occur
at=3600 Cm-1
. Such absorption occurs only in vapour
phase or in dilute solution of alcohol in non-polar
solvent. In the presence of H-bonding an intense
broad peak appear at=3600 Cm-1
.
Due to steric hindrance this compound does not have
h bonding so-OH stretch occur at 3600Cm-1
.
C-O stretching vibration in alcohol produces at 1260-
1050Cm-1
frequency of this band is used to distinguish
between primary, secondary, and tertiaary alcohol.
6. Ether
The characteristic of ether is strong C-O stretching
band at 1050-1275Cm-1
. In case of highly
asymmetrical ethers e.g. alkyl aryl ether the two C-O
band couple and show two bands for asymmetric and
symmetric stretching.
7. Carbonyl group
The carbonyl group can be recognized by a strong
absorption around 1850-1660Cm-1
.
The carbonyl group forms parts of various group such
aldehydes, ketone, acid, acid chloride, anhydride,
ester, acid amide, lactone, alctum etc.
A. Aldehydes:
Aldehydes show C=O stretching at 1730-1725 Cm-1
.
If electronegative atom is attached to α carbon of
aldehydes then it increases the frequency of vc=o. For
example.
CH3-CHO Cl3C-CHO
1730 1768 (all in Cm-1
)
In α,β unsaturated aldehydes conjugation decreases
the vc=o. freauency. for example,
CH3-CHO CH3-CH2=CH-CHO
1730 (all in Cm-1
)
CH stretching occurs at 2825Cm-1
, 2720Cm-1
as a
doublet due to fermi resonance with overtone of C-H
bending at 1390Cm-1
.
B. Ketones:
ketones show C=O stretching near at 1715Cm-1
. as
aldehydes conjugation decreases the vibration
frequency of C=O bond also decreases.
8. Carboxylic acids:
O-H stretching frequency in the solid & Pure liquid
occurs at 3300-2500Cm-1
as broad strong absorption
due to H-bonding. C=O stretching bands occurs at
1725-1700Cm-1
. This due to electron donating nature
of – OH group (+M>-I). C-O stretching occurs at
1320-1210Cm-1
.
9. Esters:
C=O stretching bands occurs at 1750-1735 Cm-1
.
Conjugation reduced the double bond character of
C=O group so vibration frequency decreases. so vc=o
of Benzoate ester is 1715 Cm-1
.
10. Acid halides:
R-CO-X, where X=F, Cl, Br, I. vc=o= 1815-1785 Cm-
1
. Since halide have – I effect greater than +M effect
so C=O stretching frequency is greater than carbony
compounds.

11. Acid anhydride:
Anhydride displays two stretching bands due to
coupled asymmetric & Symmetric stretching mode of
C=O group occurs at 1850-1800 Cm-1
and 1790-1740
Cm-1
.[5,6]
12. Amides:
All amides show C=O stretching band at 1700-
1650Cm-1
, this band is known as amide I-band.
Primary and secondary amides show N-H bending in
the region 1650-1510Cm-1
. This is known as amide II
band. All amides display C-N stretching band at
1300-1050Cm-1
, known as amide III band.
Primary amide show doublet at 3500-3400Cm-1
due
to coupled N-H stretching. Secondary amides show
singlet at near 3400 Cm-1
due to N-H H-Amines
stretching.
13. Compounds containing nitrogen:
(a). Nitro compounds: These compounds show two
very intense absorphtion bands in the 1560-1500Cm-1
and 1350-1300Cm-1
. region of the speotrum due to
asymmetric and symmetric stretcning vibrations of
the highly polar nitrogen-orygen bonds. Aromatic
nitro compounds show hands at slightly lowe
freauencies then the aliphatic compounds because of
a conjugation of the intro grup with the aromatic ring.
which slightly weakens the nitrogen-orygen bonds.
(b). Nitroso compounds: These Compounds may
represent C-NO or N-NO type. Tertiary C-nitroso
compouns tend to dimerise, and secondary and
primary C-nitroso compounds readily rearrang to
oximes. In the monomaric state they absorb in the
1600-1500Cm-1
–egion, howver, in solution they exist
preferentially as dimers and then absorb near
1290Cm-1
(cis) or 1400Cm-1
(trans).
N-Nitroso compounds show a band near 1450Cm-1
in
ccl4solution.
(c). Nitrites:These Compounds display their N=o
stretching vibration as two bands near 1660Cm-1
and
1620Cm-1
, these are attributed to the trans and cis
forms of the nitrite[7,8]
14. Hetro aromatic Compounds:
Hetroaromatics such as pyridine, furan, thiophene etc.
show C-H str bands in the region 3077-3000Cm-1
.
such compounds containing N-H group show N-H str
absorption in the region 3500-3220Cm-1
. In this
region of absorption, the exact position depends upon
the degree of hydrogen bonding and hence upon the
physical state of the sample or the polarity of the
solvent. Pyrrole and Indole in dilute solution in noon-
polar solvents show a sharp bands near 3495Cm-1
.
Ring stretching vibrations occur in the general region
between 1600-1300Cm-1
. The absorption involves
stretching and Contraction of all the bonds in the ring
and interaction between these stretching modes.
15. Amines: Amines are the alkyl derivatives of
ammonia. These can be recognised by absorption
due to N-H str in the region 3500-3300Cm-1
. The
position of absorption depends upon the degree of
hydrogen bonding. Primary amines show two
sharp bands; secondary amines give only one
band while tertiary amines do not absorb in the
said N-H str region. N-H and O-H groups have
some common properties and their absorption due
to these group are superimposed making their
identification difficult.
Since nitrogen atom is less electronegative than
oxygen atom, the N-H…N hydrogen bonds are
weaker as compared to O-H…O bonds and hence
frequency shifts due to hydrogen bonding in amine
are smaller VN
-H absorption occur at lower
freauencies amine in an inert solvent give two sharp
bands due to asymmetric stretching vibvations
between 3500-3300Cm-1
.[9,10]
Discussion
An IR spectrum is essentially a graph plotted with the
infrared light absorbed on the Y-axis against.
frequency or wavelength on the X-axis. An
illustration highlighting the different regions that light
can be classified into is given below.
IR Spectroscopy detects frequencies of infrared light
that are absorbed by a molecule. Molecules tend to
absorb these specific frequencies of light since they
correspond to the frequency of the vibration of bonds
in the molecule.
The energy required to excite the bonds belonging to
a molecule, and to make them vibrate with more
amplitude, occurs in the Infrared region. A bond will
only interact with the electromagnetic infrared
radiation, however, if it is polar.
The presence of separate areas of partial positive and
negative charge in a molecule allows the electric field
component of the electromagnetic wave to excite the
vibrational energy of the molecule.
The change in the vibrational energy leads to another
corresponding change in the dipole moment of the
given molecule. The intensity of the absorption
depends on the polarity of the bond. Symmetrical
non-polar bonds in N≡N and O=O do not absorb
radiation, as they cannot interact with an electric
field.
Most of the bands that indicate what functional group
is present are found in the region from 4000 cm-1
to
1300 cm-1
. Their bands can be identified and used to

determine the functional group of an unknown
compound.[11,12]
Bands that are unique to each molecule, similar to a
fingerprint, are found in the fingerprint region, from
1300 cm-1
to 400 cm-1
. These bands are only used to
compare the spectra of one compound to another.
The samples used in IR spectroscopy can be either in
the solid, liquid, or gaseous state.
Solid samples can be prepared by crushing the
sample with a mulling agent which has an oily
texture. A thin layer of this mull can now be
applied on a salt plate to be measured.
Liquid samples are generally kept between two
salt plates and measured since the plates are
transparent to IR light. Salt plates can be made up
of sodium chloride, calcium fluoride, or even
potassium bromide.
Since the concentration of gaseous samples can
be in parts per million, the sample cell must have
a relatively long pathlength, i.e. light must travel
for a relatively long distance in the sample cell.
Thus, samples of multiple physical states can be used
in Infrared Spectroscopy.
Results
The IR spectroscopy theory utilizes the concept that
molecules tend to absorb specific frequencies of light
that are characteristic of the corresponding structure
of the molecules. The energies are reliant on the
shape of the molecular surfaces, the associated
vibronic coupling, and the mass corresponding to the
atoms. For instance, the molecule can absorb the
energy contained in the incident light and the result is
a faster rotation or a more pronounced vibration.
Now, both of these beams are reflected to pass
through a splitter and then through a detector. Finally,
the required reading is printed out after the processor
deciphers the data passed through the detector. IR
spectroscopy involves the collection of absorption
information and its analysis in the form of a spectrum
By using computer simulations and normal mode
analysis it is possible to calculate theoretical
frequencies of molecules.
A spectrograph is often interpreted as having two
regions.
functional group region
In the functional region there are one to a few troughs
per functional group.
fingerprint region
In the fingerprint region there are many troughs
which form an intricate pattern which can be used
like a fingerprint to determine the compound.
Conclusions
Infrared spectroscopy is a simple and reliable
technique widely used in both organic and inorganic
chemistry, in research and industry. In catalysis
research it is a very useful tool to characterize the
catalyst, as well as to detect intermediates and
products during the catalytic reaction. It is used in
quality control, dynamic measurement, and
monitoring applications such as the long-term
unattended measurement of CO2 concentrations in
greenhouses and growth chambers by infrared gas
analyzers. It is also used in forensic analysis in both
criminal and civil cases, for example in identifying
polymer degradation. It can be used in determining
the blood alcohol content of a suspected drunk
driver.IR-spectroscopy has been successfully used in
analysis and identification of pigments in paintings
and other art objects such as illuminated
manuscripts.[13]
A useful way of analyzing solid samples without the
need for cutting samples uses ATR or attenuated total
reflectance spectroscopy. Using this approach,
samples are pressed against the face of a single
crystal. The infrared radiation passes through the
crystal and only interacts with the sample at the
interface between the two materials. With increasing
technology in computer filtering and manipulation of
the results, samples in solution can now be measured
accurately (water produces a broad absorbance across
the range of interest, and thus renders the spectra
unreadable without this computer treatment).Some
instruments also automatically identify the substance
being measured from a store of thousands of
reference spectra held in storage.
Infrared spectroscopy is also useful in measuring the
degree of polymerization in polymer manufacture.
Changes in the character or quantity of a particular
bond are assessed by measuring at a specific
frequency over time. Modern research instruments
can take infrared measurements across the range of
interest as frequently as 32 times a second. This can
be done whilst simultaneous measurements are made
using other techniques. This makes the observations
of chemical reactions and processes quicker and more
accurate. Infrared spectroscopy has also been
successfully utilized in the field of semiconductor
microelectronics: for example, infrared spectroscopy
can be applied to semiconductors like silicon, gallium
arsenide, gallium nitride, zinc selenide, amorphous
silicon, silicon nitride, etc. Another important
application of Infrared Spectroscopy is in the food
industry to measure the concentration of various
compounds in different food products. The

instruments are now small, and can be transported,
even for use in field trials.
Infrared Spectroscopy is also used in gas leak
detection devices such as the DP-IR and Eye CGAs.
These devices detect hydrocarbon gas leaks in the
transportation of natural gas and crude oil. In
February 2014, NASA announced a greatly upgraded
database, based on IR spectroscopy, for tracking
polycyclic aromatic hydrocarbons (PAHs) in the
universe. According to scientists, more than 20% of
the carbon in the universe may be associated with
PAHs, possible starting materials for the formation of
life. PAHs seem to have been formed shortly after the
Big Bang, are widespread throughout the universe,
and are associated with new stars and exoplanets.
Infrared spectroscopy is an important analysis method
in the recycling process of household waste plastics,
and a convenient stand-off method to sort plastic of
different polymers (PET, HDPE, ...).
Other developments include a miniature IR-
spectrometer that's linked to a cloud based database
and suitable for personal everyday use, and NIR-
spectroscopic chips that can be embedded in
smartphones and various gadgets.[14]
References
[1] Spectroscopy of Organic Compounds by
P.S.Kalsi
[2] Elementary Organic Spectroscopy by Y.R.
Sharma
[3] Spectroscopy of organic Chemistry by D.
William & I.Fleming
[4] Zeitler JA, Taday PF, Newnham DA, Pepper
M, Gordon KC, Rades T (February 2007).
"Terahertz pulsed spectroscopy and imaging in
the pharmaceutical setting--a review". The
Journal of Pharmacy and Pharmacology. 59 (2):
209–23. doi:10.1211/jpp.59.2.0008. PMID
17270075. S2CID 34705104.
[5] Atkins PW, de Paula J (2009). Elements of
physical chemistry (5th ed.). Oxford: Oxford
U.P. p. 459. ISBN 978-0-19-922672-6.
[6] Schrader B (1995). Infrared and Raman
Spectroscopy: Methods and Applications. New
York: VCH, Weinheim. p. 787. ISBN 978-3-
527-26446-9.
[7] Harwood LM, Moody CJ (1989). Experimental
organic chemistry: Principles and Practice
(Illustrated ed.). Wiley-Blackwell. p. 292.
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[8] Shadman S, Rose C, Yalin AP (2016). "Open-
path cavity ring-down spectroscopy sensor for
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(7): 194. Bibcode:2016ApPhB.122..194S.
doi:10.1007/s00340-016-6461-5. S2CID
123834102.
[9] Chromatography/Fourier transform infrared
spectroscopy and its applications, by Robert
White, p7
[10] H M Pollock and S G Kazarian,
Microspectroscopy in the Mid-Infrared, in
Encyclopedia of Analytical Chemistry (Robert
A. Meyers, Ed, 1-26 (2014), John Wiley &
Sons Ltd,
[11] Pollock Hubert M (2014). "Microspectroscopy
in the Mid-Infrared". Encyclopedia of
Analytical Chemistry. pp. 1–26.
doi:10.1002/9780470027318.a5609.pub2.
ISBN 9780470027318.
[12] H M Pollock and D A Smith, The use of near-
field probes for vibrational spectroscopy and
photothermal imaging, in Handbook of
vibrational spectroscopy, J.M. Chalmers and
P.R. Griffiths (eds), John Wiley & Sons Ltd,
Vol. 2, pp. 1472 - 1492 (2002)
[13] Krivanek OL, Lovejoy TC, Dellby N, Aoki T,
Carpenter RW, Rez P, et al. (October 2014).
"Vibrational spectroscopy in the electron
microscope". Nature. 514 (7521): 209–12.
Bibcode:2014Natur.514..209K.
doi:10.1038/nature13870. PMID 25297434.
S2CID 4467249.
[14] Idrobo JC, Lupini AR, Feng T, Unocic RR,
Walden FS, Gardiner DS, et al. (March 2018).
"Temperature Measurement by a Nanoscale
Electron Probe Using Energy Gain and Loss
Spectroscopy". Physical Review Letters. 120
(9): 095901.

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