The document provides an overview of various spectroscopy techniques, including infrared, UV/Vis, and nuclear magnetic resonance (NMR) spectroscopy, describing their principles and applications in analyzing compounds. It details the types of molecular vibrations in infrared spectroscopy as well as the Beer-Lambert law for UV/Vis spectroscopy. Additionally, it discusses the significance of NMR in organic structure determination and references important literature in the field.

1. SEEMA BRAR
ASSISTANT PROFESSOR
DEPT. OF PHARMACOGNOSY
ISF COLLEGE OF PHARMACY
WEBSITE: - WWW.ISFCP.ORG
ISF College of Pharmacy, Moga
Ghal Kalan,nGT Road, Moga- 142001, Punjab, INDIA
Internal Quality Assurance Cell - (IQAC)
INTRODUCTION TO VARIOUS
SPECTROSCOPY TECHNIQUES
Email.id : seemabrar001@gmail.com

2. SPECTROSCOPY
SPECTROSCOPY is defined as the study of the interactions between radiations and
matter as function of wavelength λ .
Interactions with particle radiation or a response of a material to an altering field
or varying frequency.
SPECTRUM : A plot of the response as a function of wavelength or more commonly
frequency is referred to as spectrum.
SPECTROMETRY : It is measurement of these responses and an instrument which
performs such measurements is a spectrophotometer or spectrograph, although
these terms are more limited in use to original field of optics from which the
concept sprang.
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3. 3Classification of methods
The type of spectroscopy depends on the study on the physical quantity measures.
Normally, the quantity is measured in intensity, either of energy absorbed or
produced.
Most spectroscopic methods are differentiated as either atomic or molecular based on
whether or not they apply to atoms or molecules. Along with that distinction, they can
be classified on the nature of their interactions:
ABSORPTION SPECTROSCOPY : It uses range of the electromagnetic spectra in
which a substance absorbs. i.e. like in NMR and IR spectroscopy.
EMISSION SPECTROSCOPY : it uses the range of electromagnetic spectra in which a
substance radiates (emits) the absorbed energy.
SCATTERING SPECTROSCOPY : it measure the amount of light a substance scatters
at certain wavelength, incident angles, and polarization angles.

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• INFRA-RED SPECTROSCOPY (IR spectroscopy) is the subset of spectroscopy
that deals with the infrared region of the electromagnetic spectrum. It covers a
range of techniques, the most common being a form of absorption spectroscopy.
As with all spectroscopic techniques, it can be used to identify compounds
or investigate sample composition.
• Infrared spectroscopy offers the possibility to measure different
types of inter atomic bond vibrations at different frequencies. Especially
in organic chemistry the analysis of IR absorption spectra shows what type
of bonds are present in the sample.
• Infrared spectroscopy exploits the fact that molecules have specific
frequencies at which they rotate or vibrate corresponding to discrete
energy levels.
Infra-Red spectroscopy

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•
Infra-Red spectroscopy

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• Molecules are made up of atoms linked by chemical bonds. The movement of atoms
and the chemical bonds are like spring and balls (vibration) . This characteristic vibration
are called Natural frequency of vibration.
• When energy in the form of infrared radiation is applied then it causes the vibration
between the atoms of the molecules and when, Applied infrared frequency = Natural
frequency of Vibration Then, Absorption of IR radiation takes place and a peak is
observed.
Different functional groups absorb characteristic frequencies of IR radiation. Hence gives
the characteristic peak value. Therefore, IR spectrum of a chemical substance is a finger
print of a molecule for its identification
Principle of IR spectroscopy

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There are 2 types of vibrations:
1.Stretching vibrations
2.Bending vibrations
Molecular vibrations
1. Stretching vibrations:
- Vibration or oscillation along the line of bond
-Change in bond length
- Occurs at higher energy: 4000-1250 cm-1
Sub-types:
a) Symmetrical stretching
b) Asymmetrical stretching

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2. Bending vibrations
• Vibration or oscillation not along the line of
bond
• These are also called as deformations
• In this, bond angle is altered
• Occurs at low energy: 1400-666 cm-1
Sub-types:
a)In plane bending: scissoring, rocking
b)Out plane bending: wagging, twisting

10. 10UV/VIS SPECTROSCOPY
• UV/Vis spectroscopy is routinely used in the quantitative determination of
solutions of transition metal ions and highly conjugated
organic compounds.
• UV/Vis spectroscopy is routinely used in the quantitative determination of
solutions of transition metal ions and highly conjugated
organic compounds.
• For the quantitative measurements, Beer-Lambert law is followed.
• The Beer-Lambert Law is useful for characterizing many compounds but
does not hold as a universal relationship for the concentration and
absorption of all substances. A 2nd order polynomial relationship
between absorption and concentration is sometimes encountered for
very large, complex molecules such as organic dyes.

11. 11Principle of UV/VIS-SPECTROSCOPY
LAMBERT’S LAW
“When a beam of light is allowed to pass through a transparent medium, the rate of
decrease of intensity with the thickness of medium is directly proportional to the intensity
of the light”
Mathematically:
-dI/ dt ᾱ I
-In . I = kt+b -------------- eq (2)
The combination of eq (1) & (2) we will get,
A= Kct
A= ℇct (K=ℇ)

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The UV radiation region extends from 10 nm to 400 nm and the visible radiation region
extends from 400 nm to 800 nm.
Near UV Region: 200 nm to 400 nm
Far UV Region: below 200 nm
Ultraviolet absorption spectra arise from transition of electron with in a molecule from a
lower level to a higher level.
-A molecule absorb ultraviolet radiation of frequency (𝜗), the electron in that molecule
undergo transition from lower to higher energy level. The energy can be calculated by
the equation,
E=h𝜗 erg
E₁-E = h𝜗ₒ

13. 13Nuclear Magnetic Resonance Spectroscopy
NMR is the most powerful tool available for organic structure determination.
Nuclear magnetic resonance spectroscopy analyzes the magnetic properties of certain
atomic nuclei to determine different electronic local environments of hydrogen, carbon, or
other atoms in an organic compound or other compound. This is used to help determine
the structure of the compound.
• It is used to study a wide variety of nuclei:
– 1H
– 13C
– 15N
– 19F
– 31P

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Magnetic phenomena
• Atomic nuclei – tiny magnets
• In external field – align or oppose
Number of nucleons
• Must be odd for residual magnetism
• For e.g. Hydrogen exhibits, Deuterium does not
Resonance condition
• Transition from low to high energy state occurs
• h = gßH
• Either a constant magnetic field is applied and
appropriate region of RF is swept
• Or a constant frequency is employed & the
external magnetic field is swept
Principle of NMR-SPECTROSCOPY

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Chemical shift
• Arises from applied field inducing secondary fieldS at the proton
by interacting with adjacent bonding electrons
• Is measured relative to an internal standard – TMS
Spin – spin splitting
• Seen in high resolution spectroscopy

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 E.D. Becker, High Resolution NMR: Theory and Chemical Applications, 3rd Edition,
Academic press, San Diego, 2000.
 P.T. Callaghan, Principles of Nuclear Magnetic Resonance Microscopy, Oxford
University Press, London, 1991.
 H. Gunther, NMR spectroscopy, 2nd Edition, John Wiley and Sons, New York, 1995.
 J.K. M. Sanders, B.M. Hunter, Modern NMR Spectroscopy – A Guide for Chemists, 2nd
Edition, Oxford University Press, Oxford, England, 1993
References

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