This document discusses ultraviolet-visible spectroscopy (UV-Vis). It begins with an introduction to UV-Vis spectroscopy and its history. The principle behind UV-Vis is then explained, noting that electrons are promoted to higher energy levels when absorbing ultraviolet or visible light. The document outlines the instrumentation used, known as a spectrophotometer, and Beer's Law which describes the relationship between absorbance and concentration. UV-Vis spectroscopy has various applications including quantitative analysis and identification of unknown compounds by comparing their spectra. The document concludes that UV-Vis is widely used in analytical chemistry.

1. By-
Manish Sahu
M.Sc. Chemistry (Final)
Sp.- Physical Chemistry
UV SPECTROSCOPY

2. SYNOPSIS
 Introduction
 History
 Principle
 Instrumentation
 Beer-Lambert Law
 Application
 Conclusion
 Reference

3. INTRODUCTION
 The electronic spectra ( Ultraviolet and
Visible ) of compound are associated with
measurement of energy absorbed when
electrons are promoted to higher energy
levels .
 The wavelength range of UV at 2000-
4000 Å .
The range of UV – visible Spectra

4. HISTORY
 “Ultraviolet” means “Beyond violet” ( from
Latin ultra “beyond” ) , violet being the colour
of the highest frequencies of visible light.
 UV radiation discovered
in 1801 when the German
Physicist Johann Wilhelm
Ritter .

5. PRINCIPLE
 UV absorption spectra arise from transition of
electron with in a molecule from a lower level to
high level .
 A molecule absorb ultraviolet radiation of
frequency (ʋ) the electron in that molecule
undergo transition from lower to high energy level.
The energy can be calculated by :
Etotal = Eelectranic + Evibrational + Erotational

6. INSTRUMENTATION
A spectrophotometer is a
device which detects the percentage
transmittance of light radiation when
light of certain intensity and frequency
range is passed through the sample .
Thus, the instrument compress the
intensity of the light with that of the
incident light .

8. BEER-LAMBERT LAW
 According to the Beer-Lambert law the
absorbance is proportional to the concentration of
the substance in solution and as a result UV –
Visible spectroscopy can also be used to measure
the concentration of a sample .
 The Beer - Lambert law can be expressed in from
of the following equation ;
A = εcl
Where;
A= Absorbance
l = Optical path length
c = Concentration of solution ( mol dm-3
)
ε = Molar extinction

9. APPLICATION
Ultraviolet Spectrophotometric methods find
extensive use in the identification of various hydrocarbons ,
vitamins, steroid, heterocyclic, and conjugated aliphatics.
 Quantitative Analysis:-
UV absorption spectroscopy can
characterise those types of compound which
absorb UV Radiation. These compounds contain
either unbounded electron ( n – electron ) or the
conjugated double bond system ( π – electron ) such
as aromatic compound .

10.  Identification of an Unknown Compound :-
An unknown compound
can be identified by comparing its spectrum with the
known spectra UV absorption method is less useful
then IR and NMR method .
 Detection of Functional Group :-
UV technique is
applied to detect presence or absence of the
chromospheres .

11. CONCLUSION
We can conclude that UV
spectroscopy is best method which routinely
used in analytical chemistry for the
quantitative determination of different
analytes , such as transition metal ions, highly
conjugated organic compound and biological .

12. REFERENCE
 “Spectroscopy” By :-
“H. Kaur”
(Page No. 314-315)
 “Elementry Organic Chemistry” By :-
“Y. R. Sharma”
(Page No. 11-17)