Ultraviolet-visible spectroscopy involves absorption of electromagnetic radiation between 200-800nm. When molecules absorb this radiation, electrons are promoted to higher energy states through electronic transitions. The Beer-Lambert law states that the rate of decrease in radiation intensity as it passes through an absorbing solution is proportional to the concentration of the solution. Chromophores are molecular regions responsible for color through absorption of visible light. Woodward-Fieser rules attempt to predict absorption maximum wavelengths based on chromophores and substituents present. UV-visible spectroscopy has applications in chemistry for identification and quantification of substances.

1. Subject
InstrumentalMethodsofAnalysis
PRINCIPLE OF
ULTRA-VIOLET VISIBLE
SPECTROSCOPY
INSTITUTE OF CHEMISTRY
SHAH ABDUL LATIF UNIVERSITY KHAIRPUR MIRS
By
MUHAMMAD SHAKAIB QURESHI
M.PHIL ORGANIC CHEMISTRY
CH-2017-717
Submitted to
PROF DR TAJNEES PIRZADA
INSTITUTE OF CHEMISTRY
SHAH ABDUL LATIF UNIVERSITY KHAIRPUR MIRS

2. Table of Content
• Introduction
• Electromagnetic Radiation
• Electronic Transition
• Beer’s Lambert Law
• Chromophore
• WoodWard Fieser Rules
• Application of UV-Visible Spectroscopy

3. Introduction
• Ultraviolet-visible
Spectroscopy
involves the
absorption of
electromagnetic
radiation of high
energy (200nm-
800nm).
• Ultraviolet (UV)
region of EMR
Spectrum Extends
from 200nm-
400nm and the
Visible regions
from 400nm-
800nm (red light)

4. Electromagnetic Radiation
 Electromagnetic
radiation consist
of discrete
packages of
energy which are
called as photons.
 A photon consists
of an oscillating
electric field (E) &
an oscillating
magnetic field (M)
which are
perpendicular to
each other.

5. Electronic Transition
EMR Interaction with Matter
• At room temperature the molecules are in the
lowest energy levels E0.
• When the molecules absorb UV-visible light from
EMR, one of the outermost electron is promoted
to higher energy state such as E1, E2, …En, etc is
called as electronic transition.

6. Possible Electronic Transition
HOMO To LUMO

11. Beer’s-Lambert Law
• The Beer-Lambert law relates the attenuation of light to
the properties of the material through which the light is
traveling.
• The Law States that “When Beam of
Monochromatic radiation is passed through a
solution of an absorbing substances, the rate of
decrease of intensity of radiation with thickness of
the absorbing solution is proportional to the
intensity of incident radiation as to the concentration
of the solution”

12. Beer’s Lambert Law Equation

13. Limitation of Beer’s lambert Law
• The linearity of the Beer-Lambert law is limited by chemical
and instrumental factors. Causes of nonlinearity include:
 Deviations in absorptivity coefficients at high concentrations
(>0.01M) due to electrostatic interactions between molecules
in close proximity
 scattering of light due to particulates in the sample
 fluorescence or phosphorescence of the sample
 Changes in refractive index at high analyte concentration
 Shifts in chemical equilibrium as a function of concentration
 Non-monochromatic radiation, deviations can be minimized
by using a relatively flat part of the absorption spectrum such
as the maximum of an absorption band stray light.

14. Electronic Spectrum

15. Chromophore
A chromophore is the part of a molecule responsible for
its colour. The chromophore is a region in the molecule where
the energy difference between two separate molecular
orbital falls within the range of the visible spectrum. Visible light
that hits the chromophore can thus be absorbed by exciting
an electron from its ground state into an excited state.

16. Chromophore Continue..

17. Chromophore Continue..

18. Chromophore Continue..

20. Auxochrome

21. Absorption & Intensity Shifts

22. Absorption & Intensity Shift

23. Woodward Fieser Rules
• Woodward's rules, are sets of empirically derived
rules which attempt to predict the wavelength of
the absorption maximum (λmax) in an ultraviolet–
visible spectrum of a given compound.
• Inputs used in the calculation are the type
of chromophores present, the substituents on the
chromophores, and shifts due to the solvent.
• It may categories
• Conjugated Dienes
• Alpha-Beta unsaturated carbonyl compounds
• Aromatics

24. Woodward Fieser Rules

25. Woodward Fieser Predicts
Woodward Fieser Rules

26. Alpha-Beta Unsaturated carbonyl

27. Example

28. Aromatics Compounds

29. Examples

30. Application

31. References
• Organic Chemistry by Bhupinder Mehta & Manju
Mehta
• Principle of Analytical Chemistry by Haq Nawaz
Bhatti
• Organic Spectroscopy and Chromatography by
M.Younas
• Google Images