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Harshit Jadav 
NIPER-Ahmedabad
• It is the branch of science that deals with the study of 
interaction of matter with light. 
OR 
• It is the branch of science that deals with the study of 
interaction of electromagnetic radiation with matter.
• 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.
• Frequency (ν): 
• It is defined as the number of times electrical 
field radiation oscillates in one second. 
• The unit for frequency is Hertz (Hz). 
1 Hz = 1 cycle per second 
• Wavelength (λ): 
• It is the distance between two nearest parts of 
the wave in the same phase i.e. distance 
between two nearest crest or troughs.
• The relationship between wavelength & 
frequency can be written as: 
c = ν λ 
• As photon is subjected to energy, so 
E = h ν = h c / λ
Violet 400 - 420 
nm 
Yellow 570 - 585 
nm 
Indigo 420 - 440 
nm 
Orange 585 - 620 
nm 
Blue 440 - 490 
nm 
Red 620 - 780 
nm
• The principle is based on the measurement 
of spectrum of a sample containing atoms / 
molecules. 
• Spectrum is a graph of intensity of 
absorbed or emitted radiation by sample 
verses frequency (ν) or wavelength (λ). 
• Spectrometer is an instrument design to 
measure the spectrum of a compound.
1. Absorption Spectroscopy: 
• An analytical technique which concerns 
with the measurement of absorption of 
electromagnetic radiation. 
• e.g. UV (185 - 400 nm) / Visible (400 - 800 
nm) Spectroscopy, IR Spectroscopy (0.76 - 
15 μm)
2. Emission Spectroscopy: 
• An analytical technique in which 
emission (of a particle or radiation) is 
dispersed according to some property of 
the emission & the amount of dispersion 
is measured. 
• e.g. Mass Spectroscopy
• When a monochromatic radiation is passed through a 
solution, the decrease in the intensity of radiation with 
thickness of the solution is directly proportional to the 
intensity of the incident light. 
• Let I be the intensity of incident radiation. 
x be the thickness of the solution. 
Then
I 
dI 
  
dx 
dI 
  
So, KI 
dx 
Integrate equation between limit 
I = Io at x = 0 and 
I = I at x=l, 
We get, 
Kl 
I 
I 
  
0 
ln
Kl 
I 
I 
  
0 
2.303 log 
l 
K 
I 
I 
2.303 
log 
0 
  
I 
 0 log 
Where, A Absorbance 
I 
E 
K 
 
2.303 
A  E.l 
Absorption coefficient 
Lambert’s Law
• When a monochromatic radiation is passed through a 
solution, the decrease in the intensity of radiation with 
thickness of the solution is directly proportional to the 
intensity of the incident light as well as concentration of 
the solution. 
• Let I be the intensity of incident radiation. 
x be the thickness of the solution. 
C be the concentration of the solution. 
Then
C I 
dI 
  . 
dx 
dI 
  ' . 
So, K C I 
dx 
Integrate equation between limit 
I = Io at x = 0 and 
I = I at x=l, 
We get, 
K C l 
I 
ln ' . 
I 
0 
 
2.303log . . 0  
K C l 
I 
I 
C l 
K 
I 
I 
. 
2.303 
log 0  
I 
Where, log 
0  A Absorbance 
I 
E 
K 
 
2.303 
A E.C.l 
Molar extinction 
coefficient 
Beer’s Law
A E.C.l 
I 
I 
T  OR A 
0 I 
 T   
I 
0 
log log 
From the equation it is seen that the absorbance 
which is also called as optical density (OD) of a solution 
in a container of fixed path length is directly 
proportional to the concentration of a solution.
• 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 
• Far UV spectroscopy is studied under vacuum 
condition. 
• The common solvent used for preparing sample to be 
analyzed is either ethyl alcohol or hexane.
1 • σ → σ* transition 
2 • π→ π* transition 
3 • n → σ* transition 
4 • n → π* transition 
5 • σ → π* transition 
6 • π→ σ* transition
1 • σ→ σ* transition 
• σ electron from orbital is excited to 
corresponding anti-bonding orbital σ*. 
• The energy required is large for this 
transition. 
• e.g. Methane (CH4) has C-H bond only 
and can undergo σ → σ* transition and 
shows absorbance maxima at 125 nm.
2 • π→ π* transition 
• π electron in a bonding orbital is excited 
to corresponding anti-bonding orbital π*. 
• Compounds containing multiple bonds 
like alkenes, alkynes, carbonyl, nitriles, 
aromatic compounds, etc undergo π → π* 
transitions. 
• e.g. Alkenes generally absorb in the 
region 170 to 205 nm.
3 • n → σ* transition 
• Saturated compounds containing atoms 
with lone pair of electrons like O, N, S 
and halogens are capable of n → σ* 
transition. 
• These transitions usually requires less 
energy than σ → σ* transitions. 
• The number of organic functional groups 
with n → σ* peaks in UV region is small
4 • n → π* transition 
• An electron from non-bonding orbital is 
promoted to anti-bonding π* orbital. 
• Compounds containing double bond 
involving hetero atoms (C=O, C≡N, N=O) 
undergo such transitions. 
• n → π* transitions require minimum 
energy and show absorption at longer 
wavelength around 300 nm.
5 • σ→ π* transition 
& • π→ σ* transition 6 
•These electronic transitions are forbidden 
transitions & are only theoretically 
possible. 
•Thus, n → π* & π → π* electronic 
transitions show absorption in region 
above 200 nm which is accessible to UV-visible 
spectrophotometer. 
•The UV spectrum is of only a few broad of
The part of a molecule responsible for imparting color, are 
called as chromospheres. 
OR 
The functional groups containing multiple bonds capable of 
absorbing radiations above 200 nm due to n → π* & π → π* 
transitions. 
e.g. NO2, N=O, C=O, C=N, C≡N, C=C, C=S, etc
To interpretate UV – visible spectrum following points 
should be noted: 
1. Non-conjugated alkenes show an intense absorption 
below 200 nm & are therefore inaccessible to UV 
spectrophotometer. 
2. Non-conjugated carbonyl group compound give a weak 
absorption band in the 200 - 300 nm region.
e.g. Acetone which has λmax = 279 nm 
H3C 
O 
C 
CH3 
and that cyclohexane has λmax = 291 nm. 
When double bonds are conjugated in a compound 
λmax is shifted to longer wavelength. 
e.g. 1,5 - hexadiene has λmax = 178 nm 
2,4 - hexadiene has λmax = 227 nm 
O 
H2C 
CH2 
H3C 
CH3
3. Conjugation of C=C and carbonyl group shifts the λmax 
of both groups to longer wavelength. 
e.g. Ethylene has λmax = 171 nm 
Acetone has λmax = 279 nm 
Crotonaldehyde has λmax = 290 nm 
H3C 
C 
CH3 
O 
H2C CH2 
C 
CH3 
O 
H2C
The functional groups attached to a chromophore which 
modifies the ability of the chromophore to absorb light , 
altering the wavelength or intensity of absorption. 
OR 
The functional group with non-bonding electrons that does 
not absorb radiation in near UV region but when attached to 
a chromophore alters the wavelength & intensity of 
absorption.
e.g. Benzene λmax = 255 nm 
Phenol λmax = 270 nm 
Aniline λmax = 280 nm 
OH 
NH2
1 • Bathochromic Shift (Red Shift) 
• When absorption maxima (λmax) of a 
compound shifts to longer wavelength, it is 
known as bathochromic shift or red shift. 
• The effect is due to presence of an 
auxochrome or by the change of solvent. 
• e.g. An auxochrome group like –OH, -OCH3 
causes absorption of compound at longer 
wavelength.
1 • Bathochromic Shift (Red Shift) 
• In alkaline medium, p-nitrophenol shows 
red shift. Because negatively charged 
oxygen delocalizes more effectively than 
the unshared pair of electron. 
+ O 
N 
OH 
- 
O 
OH 
- 
Alkaline 
medium 
+ O 
N 
O 
- 
- 
O 
p-nitrophenol 
λmax = 255 nm λmax = 265 nm
2 • Hypsochromic Shift (Blue Shift) 
• When absorption maxima (λmax) of a 
compound shifts to shorter wavelength, it is 
known as hypsochromic shift or blue shift. 
• The effect is due to presence of an group 
causes removal of conjugation or by the 
change of solvent.
2 • Hypsochromic Shift (Blue Shift) 
• Aniline shows blue shift in acidic medium, it 
loses conjugation. 
NH2 
+ 
H 
Acidic 
medium 
NH3 
+ 
Cl 
- 
Aniline 
λmax = 280 nm λmax = 265 nm
• When absorption intensity (ε) of a 
compound is increased, it is known as 
hyperchromic shift. 
• If auxochrome introduces to the compound, 
the intensity of absorption increases. 
Pyridine 2-methyl 
pyridine 
3 • Hyperchromic Effect 
N N CH3
4 • Hypochromic Effect 
• When absorption intensity (ε) of a 
compound is decreased, it is known as 
hypochromic shift. 
CH3 
Naphthalene 2-methyl 
naphthalene 
ε = 19000 ε = 10250
Wavelength ( λ ) 
Absorbance ( A ) 
Hyperchromic shift 
Hypochromic shift 
Red 
shift 
Blue 
shift 
λmax
• 1. Colorimeters 
• Inexpensive and less accurate 
• 400-700nm 
• 2. Spectrophotometer 
• Used for wide range of wavelength 
• Highly accurate 
• expensive
• Visible spectrum 400-800 nm 
• Requirements for source: 
•Should provide continuous radiation from 
400-800 nm 
•Adequate intensity 
•Stable and free from fluctuations
• 1. Tungsten lamp 
•Most widely used 
•Consist of 
tungsten filament 
in vacuum bulb 
• 2. Carbon arc 
lamp 
•High intensity 
•Also provide 
entire range of 
visible spectrum
• Light gives radiation from 400-800nm 
• This is called polychromatic light 
which is of several wavelength 
• Hence a filter or monochromater is 
used to convert polychromatic light 
into monochromatic lights used
• Filters 
•Absorption filters 
• Interference filter 
• Monochromaters 
• Prism type ( 
dispersive type or 
Littrow type) 
• Grating type 
(Diffraction grating & 
transmittance 
grating)
• Filters are made up of glass, coated with 
pigment or they are made up of dyed gelatin. 
• They absorb unwanted radiation and transmit 
the rest of the radiation which is required for 
colorimetry. 
• Merits: 
• Simple, cheaper 
• Demeits: 
• Less acurate, bandpass is more (+/- 30 nm), intensity 
is less
• Also known as fabry-perot filter 
• It has dielectric spacer made up of CaF2, MgF2, or SiO. 
• Thickness o dielectric spacer film can be ½ ʎ (1st order), 
2/2 ʎ (2nd order) , 3/2 ʎ (3rd order). 
• Mechanism is constructive interference folloved by this 
equatuion. 
ʎ=2ηb/m 
ʎ=wavelength of light 
η= dielectric constant of material 
B= layer thickness
• Band pass is +/- 10 nm 
• Transmittance is 40% 
• Merits : 
• Inexpensive, lower band pass, use of additional 
filter cut off for undesired wavelength 
• Demerits: 
• Peak transmission is low
UV Spectroscopy

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UV Spectroscopy

  • 2. • It is the branch of science that deals with the study of interaction of matter with light. OR • It is the branch of science that deals with the study of interaction of electromagnetic radiation with matter.
  • 3. • 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.
  • 4. • Frequency (ν): • It is defined as the number of times electrical field radiation oscillates in one second. • The unit for frequency is Hertz (Hz). 1 Hz = 1 cycle per second • Wavelength (λ): • It is the distance between two nearest parts of the wave in the same phase i.e. distance between two nearest crest or troughs.
  • 5. • The relationship between wavelength & frequency can be written as: c = ν λ • As photon is subjected to energy, so E = h ν = h c / λ
  • 6.
  • 7. Violet 400 - 420 nm Yellow 570 - 585 nm Indigo 420 - 440 nm Orange 585 - 620 nm Blue 440 - 490 nm Red 620 - 780 nm
  • 8. • The principle is based on the measurement of spectrum of a sample containing atoms / molecules. • Spectrum is a graph of intensity of absorbed or emitted radiation by sample verses frequency (ν) or wavelength (λ). • Spectrometer is an instrument design to measure the spectrum of a compound.
  • 9. 1. Absorption Spectroscopy: • An analytical technique which concerns with the measurement of absorption of electromagnetic radiation. • e.g. UV (185 - 400 nm) / Visible (400 - 800 nm) Spectroscopy, IR Spectroscopy (0.76 - 15 μm)
  • 10. 2. Emission Spectroscopy: • An analytical technique in which emission (of a particle or radiation) is dispersed according to some property of the emission & the amount of dispersion is measured. • e.g. Mass Spectroscopy
  • 11.
  • 12. • When a monochromatic radiation is passed through a solution, the decrease in the intensity of radiation with thickness of the solution is directly proportional to the intensity of the incident light. • Let I be the intensity of incident radiation. x be the thickness of the solution. Then
  • 13. I dI   dx dI   So, KI dx Integrate equation between limit I = Io at x = 0 and I = I at x=l, We get, Kl I I   0 ln
  • 14. Kl I I   0 2.303 log l K I I 2.303 log 0   I  0 log Where, A Absorbance I E K  2.303 A  E.l Absorption coefficient Lambert’s Law
  • 15. • When a monochromatic radiation is passed through a solution, the decrease in the intensity of radiation with thickness of the solution is directly proportional to the intensity of the incident light as well as concentration of the solution. • Let I be the intensity of incident radiation. x be the thickness of the solution. C be the concentration of the solution. Then
  • 16. C I dI   . dx dI   ' . So, K C I dx Integrate equation between limit I = Io at x = 0 and I = I at x=l, We get, K C l I ln ' . I 0  
  • 17. 2.303log . . 0  K C l I I C l K I I . 2.303 log 0  I Where, log 0  A Absorbance I E K  2.303 A E.C.l Molar extinction coefficient Beer’s Law
  • 18. A E.C.l I I T  OR A 0 I  T   I 0 log log From the equation it is seen that the absorbance which is also called as optical density (OD) of a solution in a container of fixed path length is directly proportional to the concentration of a solution.
  • 19. • 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 • Far UV spectroscopy is studied under vacuum condition. • The common solvent used for preparing sample to be analyzed is either ethyl alcohol or hexane.
  • 20.
  • 21. 1 • σ → σ* transition 2 • π→ π* transition 3 • n → σ* transition 4 • n → π* transition 5 • σ → π* transition 6 • π→ σ* transition
  • 22. 1 • σ→ σ* transition • σ electron from orbital is excited to corresponding anti-bonding orbital σ*. • The energy required is large for this transition. • e.g. Methane (CH4) has C-H bond only and can undergo σ → σ* transition and shows absorbance maxima at 125 nm.
  • 23. 2 • π→ π* transition • π electron in a bonding orbital is excited to corresponding anti-bonding orbital π*. • Compounds containing multiple bonds like alkenes, alkynes, carbonyl, nitriles, aromatic compounds, etc undergo π → π* transitions. • e.g. Alkenes generally absorb in the region 170 to 205 nm.
  • 24. 3 • n → σ* transition • Saturated compounds containing atoms with lone pair of electrons like O, N, S and halogens are capable of n → σ* transition. • These transitions usually requires less energy than σ → σ* transitions. • The number of organic functional groups with n → σ* peaks in UV region is small
  • 25. 4 • n → π* transition • An electron from non-bonding orbital is promoted to anti-bonding π* orbital. • Compounds containing double bond involving hetero atoms (C=O, C≡N, N=O) undergo such transitions. • n → π* transitions require minimum energy and show absorption at longer wavelength around 300 nm.
  • 26. 5 • σ→ π* transition & • π→ σ* transition 6 •These electronic transitions are forbidden transitions & are only theoretically possible. •Thus, n → π* & π → π* electronic transitions show absorption in region above 200 nm which is accessible to UV-visible spectrophotometer. •The UV spectrum is of only a few broad of
  • 27. The part of a molecule responsible for imparting color, are called as chromospheres. OR The functional groups containing multiple bonds capable of absorbing radiations above 200 nm due to n → π* & π → π* transitions. e.g. NO2, N=O, C=O, C=N, C≡N, C=C, C=S, etc
  • 28. To interpretate UV – visible spectrum following points should be noted: 1. Non-conjugated alkenes show an intense absorption below 200 nm & are therefore inaccessible to UV spectrophotometer. 2. Non-conjugated carbonyl group compound give a weak absorption band in the 200 - 300 nm region.
  • 29. e.g. Acetone which has λmax = 279 nm H3C O C CH3 and that cyclohexane has λmax = 291 nm. When double bonds are conjugated in a compound λmax is shifted to longer wavelength. e.g. 1,5 - hexadiene has λmax = 178 nm 2,4 - hexadiene has λmax = 227 nm O H2C CH2 H3C CH3
  • 30. 3. Conjugation of C=C and carbonyl group shifts the λmax of both groups to longer wavelength. e.g. Ethylene has λmax = 171 nm Acetone has λmax = 279 nm Crotonaldehyde has λmax = 290 nm H3C C CH3 O H2C CH2 C CH3 O H2C
  • 31. The functional groups attached to a chromophore which modifies the ability of the chromophore to absorb light , altering the wavelength or intensity of absorption. OR The functional group with non-bonding electrons that does not absorb radiation in near UV region but when attached to a chromophore alters the wavelength & intensity of absorption.
  • 32. e.g. Benzene λmax = 255 nm Phenol λmax = 270 nm Aniline λmax = 280 nm OH NH2
  • 33.
  • 34. 1 • Bathochromic Shift (Red Shift) • When absorption maxima (λmax) of a compound shifts to longer wavelength, it is known as bathochromic shift or red shift. • The effect is due to presence of an auxochrome or by the change of solvent. • e.g. An auxochrome group like –OH, -OCH3 causes absorption of compound at longer wavelength.
  • 35. 1 • Bathochromic Shift (Red Shift) • In alkaline medium, p-nitrophenol shows red shift. Because negatively charged oxygen delocalizes more effectively than the unshared pair of electron. + O N OH - O OH - Alkaline medium + O N O - - O p-nitrophenol λmax = 255 nm λmax = 265 nm
  • 36. 2 • Hypsochromic Shift (Blue Shift) • When absorption maxima (λmax) of a compound shifts to shorter wavelength, it is known as hypsochromic shift or blue shift. • The effect is due to presence of an group causes removal of conjugation or by the change of solvent.
  • 37. 2 • Hypsochromic Shift (Blue Shift) • Aniline shows blue shift in acidic medium, it loses conjugation. NH2 + H Acidic medium NH3 + Cl - Aniline λmax = 280 nm λmax = 265 nm
  • 38. • When absorption intensity (ε) of a compound is increased, it is known as hyperchromic shift. • If auxochrome introduces to the compound, the intensity of absorption increases. Pyridine 2-methyl pyridine 3 • Hyperchromic Effect N N CH3
  • 39. 4 • Hypochromic Effect • When absorption intensity (ε) of a compound is decreased, it is known as hypochromic shift. CH3 Naphthalene 2-methyl naphthalene ε = 19000 ε = 10250
  • 40. Wavelength ( λ ) Absorbance ( A ) Hyperchromic shift Hypochromic shift Red shift Blue shift λmax
  • 41.
  • 42. • 1. Colorimeters • Inexpensive and less accurate • 400-700nm • 2. Spectrophotometer • Used for wide range of wavelength • Highly accurate • expensive
  • 43. • Visible spectrum 400-800 nm • Requirements for source: •Should provide continuous radiation from 400-800 nm •Adequate intensity •Stable and free from fluctuations
  • 44. • 1. Tungsten lamp •Most widely used •Consist of tungsten filament in vacuum bulb • 2. Carbon arc lamp •High intensity •Also provide entire range of visible spectrum
  • 45. • Light gives radiation from 400-800nm • This is called polychromatic light which is of several wavelength • Hence a filter or monochromater is used to convert polychromatic light into monochromatic lights used
  • 46. • Filters •Absorption filters • Interference filter • Monochromaters • Prism type ( dispersive type or Littrow type) • Grating type (Diffraction grating & transmittance grating)
  • 47. • Filters are made up of glass, coated with pigment or they are made up of dyed gelatin. • They absorb unwanted radiation and transmit the rest of the radiation which is required for colorimetry. • Merits: • Simple, cheaper • Demeits: • Less acurate, bandpass is more (+/- 30 nm), intensity is less
  • 48. • Also known as fabry-perot filter • It has dielectric spacer made up of CaF2, MgF2, or SiO. • Thickness o dielectric spacer film can be ½ ʎ (1st order), 2/2 ʎ (2nd order) , 3/2 ʎ (3rd order). • Mechanism is constructive interference folloved by this equatuion. ʎ=2ηb/m ʎ=wavelength of light η= dielectric constant of material B= layer thickness
  • 49. • Band pass is +/- 10 nm • Transmittance is 40% • Merits : • Inexpensive, lower band pass, use of additional filter cut off for undesired wavelength • Demerits: • Peak transmission is low