U V Visible Spectroscopy
-
Upload
nandakumar-gopinathan -
Category
Science
-
view
33 -
download
1
Transcript of U V Visible Spectroscopy
![Page 1: U V Visible Spectroscopy](https://reader037.fdocuments.us/reader037/viewer/2022102808/55d204a7bb61eb7a438b472c/html5/thumbnails/1.jpg)
UV / Visible Spectroscopy
Presented By Nandakumar V.G Mphil student Dept.of Opto electronics. Kerala University,
Kariavattom .
![Page 2: U V Visible Spectroscopy](https://reader037.fdocuments.us/reader037/viewer/2022102808/55d204a7bb61eb7a438b472c/html5/thumbnails/2.jpg)
Contents.
• Introduction• Electromagnetic Radiation• Basic Principle• Electronic Transitions• Instrumentation• Interpretations• Advantages and Disadvantages• Applications• Conclusion.
![Page 3: U V Visible Spectroscopy](https://reader037.fdocuments.us/reader037/viewer/2022102808/55d204a7bb61eb7a438b472c/html5/thumbnails/3.jpg)
Introduction
• The history of spectroscopy began with Isaac Newton's optics experiments (1666–1672). Newton applied the word "spectrum" to describe the rainbow of colors that combine to form white light and that are revealed when the white light is passed through a prism. During the early 1800s, Joseph von made experimental advances with dispersive spectrometers that enabled spectroscopy to become a more precise and quantitative scientific technique. Since then, spectroscopy has played and continues to play a significant role in chemistry, physics and astronomy.
![Page 4: U V Visible Spectroscopy](https://reader037.fdocuments.us/reader037/viewer/2022102808/55d204a7bb61eb7a438b472c/html5/thumbnails/4.jpg)
Spectroscopy
• 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.
![Page 5: U V Visible Spectroscopy](https://reader037.fdocuments.us/reader037/viewer/2022102808/55d204a7bb61eb7a438b472c/html5/thumbnails/5.jpg)
Four common spectroscopic techniques use to determine structure:
• UV/Visible Spectroscopy
• Infrared Spectroscopy (IR)
• Nuclear Magnetic Resonance Spectroscopy (NMR)
• Mass Spectrometry (MS or Mass Spec)
![Page 6: U V Visible Spectroscopy](https://reader037.fdocuments.us/reader037/viewer/2022102808/55d204a7bb61eb7a438b472c/html5/thumbnails/6.jpg)
Electromagnetic Radiation
![Page 7: U V Visible Spectroscopy](https://reader037.fdocuments.us/reader037/viewer/2022102808/55d204a7bb61eb7a438b472c/html5/thumbnails/7.jpg)
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.
![Page 8: U V Visible Spectroscopy](https://reader037.fdocuments.us/reader037/viewer/2022102808/55d204a7bb61eb7a438b472c/html5/thumbnails/8.jpg)
![Page 9: U V Visible Spectroscopy](https://reader037.fdocuments.us/reader037/viewer/2022102808/55d204a7bb61eb7a438b472c/html5/thumbnails/9.jpg)
Electromagnetic Radiation
• 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.
![Page 10: U V Visible Spectroscopy](https://reader037.fdocuments.us/reader037/viewer/2022102808/55d204a7bb61eb7a438b472c/html5/thumbnails/10.jpg)
Electromagnetic Radiation
• 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
![Page 11: U V Visible Spectroscopy](https://reader037.fdocuments.us/reader037/viewer/2022102808/55d204a7bb61eb7a438b472c/html5/thumbnails/11.jpg)
Electromagnetic Radiation
![Page 12: U V Visible Spectroscopy](https://reader037.fdocuments.us/reader037/viewer/2022102808/55d204a7bb61eb7a438b472c/html5/thumbnails/12.jpg)
Electromagnetic Radiation
Violet 400 - 420 nm Yellow 570 - 585 nm
Indigo 420 - 440 nm Orange 585 - 620 nm
Blue 440 - 490 nm Red 620 - 780 nm
Green 490 - 570 nm
![Page 13: U V Visible Spectroscopy](https://reader037.fdocuments.us/reader037/viewer/2022102808/55d204a7bb61eb7a438b472c/html5/thumbnails/13.jpg)
Principles of Spectroscopy
![Page 14: U V Visible Spectroscopy](https://reader037.fdocuments.us/reader037/viewer/2022102808/55d204a7bb61eb7a438b472c/html5/thumbnails/14.jpg)
Principles of Spectroscopy
• 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.
![Page 15: U V Visible Spectroscopy](https://reader037.fdocuments.us/reader037/viewer/2022102808/55d204a7bb61eb7a438b472c/html5/thumbnails/15.jpg)
Principles of Spectroscopy
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)
![Page 16: U V Visible Spectroscopy](https://reader037.fdocuments.us/reader037/viewer/2022102808/55d204a7bb61eb7a438b472c/html5/thumbnails/16.jpg)
Principles of Spectroscopy
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
![Page 17: U V Visible Spectroscopy](https://reader037.fdocuments.us/reader037/viewer/2022102808/55d204a7bb61eb7a438b472c/html5/thumbnails/17.jpg)
Interaction of EMR with
Matter
![Page 18: U V Visible Spectroscopy](https://reader037.fdocuments.us/reader037/viewer/2022102808/55d204a7bb61eb7a438b472c/html5/thumbnails/18.jpg)
Interaction of EMR with matter1. Electronic Energy Levels:• 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 bond / lone pair electron is promoted to higher energy state such as E1, E2, …En, etc is called as electronic transition and the difference is as:∆E = h ν = En - E0 where (n = 1, 2, 3, … etc)
∆E = 35 to 71 kcal/mole
![Page 19: U V Visible Spectroscopy](https://reader037.fdocuments.us/reader037/viewer/2022102808/55d204a7bb61eb7a438b472c/html5/thumbnails/19.jpg)
![Page 20: U V Visible Spectroscopy](https://reader037.fdocuments.us/reader037/viewer/2022102808/55d204a7bb61eb7a438b472c/html5/thumbnails/20.jpg)
Interaction of EMR with matter
2. Vibrational Energy Levels:• These are less energy level than electronic
energy levels.
• The spacing between energy levels are relatively small i.e. 0.01 to 10 kcal/mole.
• e.g. when IR radiation is absorbed, molecules are excited from one vibrational level to another or it vibrates with higher amplitude.
![Page 21: U V Visible Spectroscopy](https://reader037.fdocuments.us/reader037/viewer/2022102808/55d204a7bb61eb7a438b472c/html5/thumbnails/21.jpg)
Interaction of EMR with matter
3. Rotational Energy Levels:• These energy levels are quantized & discrete.
• The spacing between energy levels are even smaller than vibrational energy levels.
∆Erotational < ∆Evibrational < ∆Eelectronic
![Page 22: U V Visible Spectroscopy](https://reader037.fdocuments.us/reader037/viewer/2022102808/55d204a7bb61eb7a438b472c/html5/thumbnails/22.jpg)
Energy levels
![Page 23: U V Visible Spectroscopy](https://reader037.fdocuments.us/reader037/viewer/2022102808/55d204a7bb61eb7a438b472c/html5/thumbnails/23.jpg)
![Page 24: U V Visible Spectroscopy](https://reader037.fdocuments.us/reader037/viewer/2022102808/55d204a7bb61eb7a438b472c/html5/thumbnails/24.jpg)
Lambert’sLaw
![Page 25: U V Visible Spectroscopy](https://reader037.fdocuments.us/reader037/viewer/2022102808/55d204a7bb61eb7a438b472c/html5/thumbnails/25.jpg)
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.
• Let I be the intensity of incident radiation.x be the thickness of the solution.
Then
![Page 26: U V Visible Spectroscopy](https://reader037.fdocuments.us/reader037/viewer/2022102808/55d204a7bb61eb7a438b472c/html5/thumbnails/26.jpg)
Lambert’s Law
Idx
dI
So, KIdx
dI
Integrate equation between limit I = Io at x = 0 and
I = I at x=l,We get,
KlI
I
0
ln
![Page 27: U V Visible Spectroscopy](https://reader037.fdocuments.us/reader037/viewer/2022102808/55d204a7bb61eb7a438b472c/html5/thumbnails/27.jpg)
Lambert’s LawKl
I
I
0
log303.2
lK
I
I
303.2log
0
Where, AbsorbanceAI
I0log
EK
303.2
lEA .
Absorption coefficient
Lambert’s Law
![Page 28: U V Visible Spectroscopy](https://reader037.fdocuments.us/reader037/viewer/2022102808/55d204a7bb61eb7a438b472c/html5/thumbnails/28.jpg)
Beer’sLaw
![Page 29: U V Visible Spectroscopy](https://reader037.fdocuments.us/reader037/viewer/2022102808/55d204a7bb61eb7a438b472c/html5/thumbnails/29.jpg)
Beer’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
![Page 30: U V Visible Spectroscopy](https://reader037.fdocuments.us/reader037/viewer/2022102808/55d204a7bb61eb7a438b472c/html5/thumbnails/30.jpg)
Beer’s Law
ICdx
dI.
So, ICKdx
dI.'
Integrate equation between limit I = Io at x = 0 and
I = I at x=l,We get,
lCKI
I.'ln
0
![Page 31: U V Visible Spectroscopy](https://reader037.fdocuments.us/reader037/viewer/2022102808/55d204a7bb61eb7a438b472c/html5/thumbnails/31.jpg)
Beer’s Law
lCKI
I..log303.2 0
lCK
I
I.
303.2log 0
Where, AbsorbanceAI
I0log
EK
303.2
lCEA ..
Molar extinction coefficient
Beer’s Law
![Page 32: U V Visible Spectroscopy](https://reader037.fdocuments.us/reader037/viewer/2022102808/55d204a7bb61eb7a438b472c/html5/thumbnails/32.jpg)
Beer’s LawlCEA ..
0I
IT OR A
I
IT
0
loglog
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.
![Page 33: U V Visible Spectroscopy](https://reader037.fdocuments.us/reader037/viewer/2022102808/55d204a7bb61eb7a438b472c/html5/thumbnails/33.jpg)
![Page 34: U V Visible Spectroscopy](https://reader037.fdocuments.us/reader037/viewer/2022102808/55d204a7bb61eb7a438b472c/html5/thumbnails/34.jpg)
PRINCIPLES OF UV - VISIBLE SPECTROSCOPY
![Page 35: U V Visible Spectroscopy](https://reader037.fdocuments.us/reader037/viewer/2022102808/55d204a7bb61eb7a438b472c/html5/thumbnails/35.jpg)
Principle• 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 nmFar 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.
![Page 36: U V Visible Spectroscopy](https://reader037.fdocuments.us/reader037/viewer/2022102808/55d204a7bb61eb7a438b472c/html5/thumbnails/36.jpg)
04/18/2023 UV-VISIBLE SPECTROSCOPY 36
• In order to obtain a UV-VIS spectrum the sample is ideally irradiated with the electromagnetic radiation varied over a range of wavelength.
• A monochromatic radiation i.e., a radiation of a single wavelength is employed at a time.
• This process is called scanning. • The amount of the radiation absorbed at each wavelength is
measured and plotted against the wavelength to obtain the spectrum.
• Thus, a typical UV spectrum is a plot of wavelength or frequency versus the intensity of absorption.
CHARECTERISTICS OF SPECTRUM
![Page 37: U V Visible Spectroscopy](https://reader037.fdocuments.us/reader037/viewer/2022102808/55d204a7bb61eb7a438b472c/html5/thumbnails/37.jpg)
04/18/2023 UV-VISIBLE SPECTROSCOPY 37
• The UV spectra of substances are characterised by two major parameters, namely, the position of the maximum of the absorption band called λmax, and the intensity of the bands.
• The λmax refers to the wavelength of the most absorbed radiation and is a measure of the difference in the electronic energy levels involved in the transition.
• The intensity on the other hand is indicative of the probability of the transition i.e., whether the transition is allowed or not.
• It is also is a measure of the concentration of the absorbing species.
CHARECTERISTICS OF SPECTRUM
![Page 38: U V Visible Spectroscopy](https://reader037.fdocuments.us/reader037/viewer/2022102808/55d204a7bb61eb7a438b472c/html5/thumbnails/38.jpg)
04/18/2023 UV-VISIBLE SPECTROSCOPY 38
• The wavelength of the radiation absorbed by an organic molecule is determined by the difference in energy between the ground state and the various excited electronic states of the molecule.
• In organic molecules that the constituent atoms are bonded through σ and π bonds.
• In addition, these have nonbonding electrons on the atoms like, N,O,S and halogens etc.
• There are a number of transitions possible involving the bonding and the nonbonding electrons.
ORGANIC ABSORPTION
![Page 39: U V Visible Spectroscopy](https://reader037.fdocuments.us/reader037/viewer/2022102808/55d204a7bb61eb7a438b472c/html5/thumbnails/39.jpg)
Electronic Transitions
![Page 40: U V Visible Spectroscopy](https://reader037.fdocuments.us/reader037/viewer/2022102808/55d204a7bb61eb7a438b472c/html5/thumbnails/40.jpg)
The possible electronic transitions can graphically shown as:
![Page 41: U V Visible Spectroscopy](https://reader037.fdocuments.us/reader037/viewer/2022102808/55d204a7bb61eb7a438b472c/html5/thumbnails/41.jpg)
• σ → σ* transition1
• π → π* transition2
• n → σ* transition3
• n → π* transition4• σ → π* transition5• π → σ* transition6
The possible electronic transitions are
![Page 42: U V Visible Spectroscopy](https://reader037.fdocuments.us/reader037/viewer/2022102808/55d204a7bb61eb7a438b472c/html5/thumbnails/42.jpg)
• 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.
• σ → σ* transition1
![Page 43: U V Visible Spectroscopy](https://reader037.fdocuments.us/reader037/viewer/2022102808/55d204a7bb61eb7a438b472c/html5/thumbnails/43.jpg)
• 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.
• π → π* transition2
![Page 44: U V Visible Spectroscopy](https://reader037.fdocuments.us/reader037/viewer/2022102808/55d204a7bb61eb7a438b472c/html5/thumbnails/44.jpg)
• 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 (150 – 250 nm).
• n → σ* transition3
![Page 45: U V Visible Spectroscopy](https://reader037.fdocuments.us/reader037/viewer/2022102808/55d204a7bb61eb7a438b472c/html5/thumbnails/45.jpg)
• 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.
• n → π* transition4
![Page 46: U V Visible Spectroscopy](https://reader037.fdocuments.us/reader037/viewer/2022102808/55d204a7bb61eb7a438b472c/html5/thumbnails/46.jpg)
•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 absorption.
• σ → π* transition5• π → σ* transition 6&
![Page 47: U V Visible Spectroscopy](https://reader037.fdocuments.us/reader037/viewer/2022102808/55d204a7bb61eb7a438b472c/html5/thumbnails/47.jpg)
![Page 48: U V Visible Spectroscopy](https://reader037.fdocuments.us/reader037/viewer/2022102808/55d204a7bb61eb7a438b472c/html5/thumbnails/48.jpg)
Components of spectrophotometer Source Monochromator Sample compartment Detector Recorder
INSTRUMENTATION
![Page 49: U V Visible Spectroscopy](https://reader037.fdocuments.us/reader037/viewer/2022102808/55d204a7bb61eb7a438b472c/html5/thumbnails/49.jpg)
Block Diagram
RADIANT SOURCE
WAVELENGTHSELECTOR SOLVENT PHOTO-
DETECTORREADOUT
SAMPLE
Fig.-block diagram of instrumentation of UV-spectrophotometer
![Page 50: U V Visible Spectroscopy](https://reader037.fdocuments.us/reader037/viewer/2022102808/55d204a7bb61eb7a438b472c/html5/thumbnails/50.jpg)
![Page 51: U V Visible Spectroscopy](https://reader037.fdocuments.us/reader037/viewer/2022102808/55d204a7bb61eb7a438b472c/html5/thumbnails/51.jpg)
Tungsten filament lamps and Hydrogen-Deuterium lamps are
most widely used and suitable light source as they cover the whole UV region. Tungsten filament lamps are rich in red radiations; more specifically they emit the radiations of 375 nm, while the intensity of Hydrogen-Deuterium lamps falls below 375 nm.
Problem-• Due to evaporation of tungsten life period decreases.• It is overcome by using tungsten-halogen lamp.• Halogen gas prevents evaporation of tungsten.
RADIATION SOURCE
![Page 52: U V Visible Spectroscopy](https://reader037.fdocuments.us/reader037/viewer/2022102808/55d204a7bb61eb7a438b472c/html5/thumbnails/52.jpg)
![Page 53: U V Visible Spectroscopy](https://reader037.fdocuments.us/reader037/viewer/2022102808/55d204a7bb61eb7a438b472c/html5/thumbnails/53.jpg)
- Monochromators generally composed of prisms and slits. The most of the spectrophotometers are double beam spectrophotometers. The radiation emitted from the primary source is dispersed with the help of rotating prisms. The various wavelengths of the light source which are separated by the prism are then selected by the slits such the rotation of the prism results in a series of continuously increasing wavelength to pass through the slits for recording purpose. The beam selected by the slit is monochromatic and further divided into two beams with the help of another prism..
Monochromator
![Page 54: U V Visible Spectroscopy](https://reader037.fdocuments.us/reader037/viewer/2022102808/55d204a7bb61eb7a438b472c/html5/thumbnails/54.jpg)
All Monochromators contain the following component parts;
• An entrance slit• A collimating lens• A dispersing device (a prism or a grating)• A focusing lens• An exit slit
![Page 55: U V Visible Spectroscopy](https://reader037.fdocuments.us/reader037/viewer/2022102808/55d204a7bb61eb7a438b472c/html5/thumbnails/55.jpg)
Filters – a)Glass filters- Made from pieces of colored glass which transmit limited wave length range of spectrum. Wide band width 150nm.
b)Gelatin filters- Consist of mixture of dyes placed in gelatin & sandwiched between glass plates. Band width 25nm.
c)Inter ferometric filters- Band width 15nm
Prisms- -Prism bends the monochromatic light. -Amount of deviation depends on wavelength -They produce non linear dispersion.
![Page 56: U V Visible Spectroscopy](https://reader037.fdocuments.us/reader037/viewer/2022102808/55d204a7bb61eb7a438b472c/html5/thumbnails/56.jpg)
A variety of sample cells available for UV region. The choice of sample cell is based ona) the path length, shape, sizeb) the transmission characteristics at the desired wavelengthc) the relative expense
• One of the two divided beams is passed through the sample solution and second beam is passé through the reference solution. Both sample and reference solution are contained in the cells. These cells are made of either silica or quartz. Glass can't be used for the cells as it also absorbs light in the UV region. The thickness of the cell is generally 1 cm. cells may be rectangular in shape or cylindrical with flat ends.
Sample and reference cells-
![Page 57: U V Visible Spectroscopy](https://reader037.fdocuments.us/reader037/viewer/2022102808/55d204a7bb61eb7a438b472c/html5/thumbnails/57.jpg)
![Page 58: U V Visible Spectroscopy](https://reader037.fdocuments.us/reader037/viewer/2022102808/55d204a7bb61eb7a438b472c/html5/thumbnails/58.jpg)
Generally two photocells serve the purpose of detector in UV spectroscopy. One of the photocell receives the beam from sample cell and second detector receives the beam from the reference. The intensity of the radiation from the reference cell is stronger than the beam of sample cell. This results in the generation of pulsating or alternating currents in the photocells.Three common types of detectors are used.
I. Barrier layer cell II. Photo cell detector III. Photomultiplier cells
DETECTORS
![Page 59: U V Visible Spectroscopy](https://reader037.fdocuments.us/reader037/viewer/2022102808/55d204a7bb61eb7a438b472c/html5/thumbnails/59.jpg)
1. Barrier layer cells
It consist of flat Cu or Fe electrode on which semiconductor such as selenium is deposited. on the selenium a thin layer of silver or gold is sputtered over the surface.
![Page 60: U V Visible Spectroscopy](https://reader037.fdocuments.us/reader037/viewer/2022102808/55d204a7bb61eb7a438b472c/html5/thumbnails/60.jpg)
2.
![Page 61: U V Visible Spectroscopy](https://reader037.fdocuments.us/reader037/viewer/2022102808/55d204a7bb61eb7a438b472c/html5/thumbnails/61.jpg)
3. Photomultiplier
Photomultipliers have an internal amplification that gives them great sensitivity and a wide spectral range. Light causes emission of electrons from a photocathode which accelerate past a series of dynodes maintained at progressively increasing potentials.
![Page 62: U V Visible Spectroscopy](https://reader037.fdocuments.us/reader037/viewer/2022102808/55d204a7bb61eb7a438b472c/html5/thumbnails/62.jpg)
Amplifier
• Amplifier- The alternating current generated in the photocells is transferred to the amplifier. The amplifier is coupled to a small servometer. Generally current generated in the photocells is of very low intensity, the main purpose of amplifier is to amplify the signals many times so we can get clear and recordable signals.
![Page 63: U V Visible Spectroscopy](https://reader037.fdocuments.us/reader037/viewer/2022102808/55d204a7bb61eb7a438b472c/html5/thumbnails/63.jpg)
Recording Device
•
• Recording devices- Most of the time amplifier is coupled to a pen recorder which is connected to the computer. Computer stores all the data generated and produces the spectrum of the desired compound.
![Page 64: U V Visible Spectroscopy](https://reader037.fdocuments.us/reader037/viewer/2022102808/55d204a7bb61eb7a438b472c/html5/thumbnails/64.jpg)
Over all arrangements
![Page 65: U V Visible Spectroscopy](https://reader037.fdocuments.us/reader037/viewer/2022102808/55d204a7bb61eb7a438b472c/html5/thumbnails/65.jpg)
Terms used in UV / Visible Spectroscopy
![Page 66: U V Visible Spectroscopy](https://reader037.fdocuments.us/reader037/viewer/2022102808/55d204a7bb61eb7a438b472c/html5/thumbnails/66.jpg)
ChromophoreThe part of a molecule responsible for imparting color, are called as chromospheres.
ORThe 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
![Page 67: U V Visible Spectroscopy](https://reader037.fdocuments.us/reader037/viewer/2022102808/55d204a7bb61eb7a438b472c/html5/thumbnails/67.jpg)
ChromophoreTo 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.
![Page 68: U V Visible Spectroscopy](https://reader037.fdocuments.us/reader037/viewer/2022102808/55d204a7bb61eb7a438b472c/html5/thumbnails/68.jpg)
Chromophoree.g. Acetone which has λmax = 279 nm
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
CH3
CCH3
OO
CH2
CH2CH3
CH3
![Page 69: U V Visible Spectroscopy](https://reader037.fdocuments.us/reader037/viewer/2022102808/55d204a7bb61eb7a438b472c/html5/thumbnails/69.jpg)
Chromophore3. 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
CH3
CCH3
O
CH2 CH2
CCH3
O
CH2
![Page 70: U V Visible Spectroscopy](https://reader037.fdocuments.us/reader037/viewer/2022102808/55d204a7bb61eb7a438b472c/html5/thumbnails/70.jpg)
AuxochromeThe functional groups attached to a chromophore which modifies the ability of the chromophore to absorb light , altering the wavelength or intensity of absorption.
ORThe 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.
![Page 71: U V Visible Spectroscopy](https://reader037.fdocuments.us/reader037/viewer/2022102808/55d204a7bb61eb7a438b472c/html5/thumbnails/71.jpg)
Auxochromee.g. Benzene λmax = 255 nm
Phenol λmax = 270 nm
Aniline λmax = 280 nm
OH
NH2
![Page 72: U V Visible Spectroscopy](https://reader037.fdocuments.us/reader037/viewer/2022102808/55d204a7bb61eb7a438b472c/html5/thumbnails/72.jpg)
Absorption & Intensity Shifts
![Page 73: U V Visible Spectroscopy](https://reader037.fdocuments.us/reader037/viewer/2022102808/55d204a7bb61eb7a438b472c/html5/thumbnails/73.jpg)
1 • Bathochromic Shift
(Red Shift)
2 • Hypsochromic Shift
(Blue Shift)
3 • Hyperchromic Effect
4 • Hypochromic Effect
![Page 74: U V Visible Spectroscopy](https://reader037.fdocuments.us/reader037/viewer/2022102808/55d204a7bb61eb7a438b472c/html5/thumbnails/74.jpg)
• 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.
• Bathochromic Shift (Red Shift)1
![Page 75: U V Visible Spectroscopy](https://reader037.fdocuments.us/reader037/viewer/2022102808/55d204a7bb61eb7a438b472c/html5/thumbnails/75.jpg)
• In alkaline medium, p-nitrophenol shows red shift. Because negatively charged oxygen delocalizes more effectively than the unshared pair of electron.
p-nitrophenolλmax = 255 nm λmax = 265 nm
• Bathochromic Shift (Red Shift)1
OH
N+ O
-O
OH-
Alkaline
mediumO
-
N+ O
-O
![Page 76: U V Visible Spectroscopy](https://reader037.fdocuments.us/reader037/viewer/2022102808/55d204a7bb61eb7a438b472c/html5/thumbnails/76.jpg)
• 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.
• Hypsochromic Shift (Blue Shift)2
![Page 77: U V Visible Spectroscopy](https://reader037.fdocuments.us/reader037/viewer/2022102808/55d204a7bb61eb7a438b472c/html5/thumbnails/77.jpg)
• Aniline shows blue shift in acidic medium, it loses conjugation.
Anilineλmax = 280 nm λmax = 265 nm
• Hypsochromic Shift (Blue Shift)2
NH2H
+
Acidic
medium
NH3+Cl
-
![Page 78: U V Visible Spectroscopy](https://reader037.fdocuments.us/reader037/viewer/2022102808/55d204a7bb61eb7a438b472c/html5/thumbnails/78.jpg)
• 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
λmax = 257 nm λmax = 260 nmε = 2750 ε = 3560
• Hyperchromic Effect3
N N CH3
![Page 79: U V Visible Spectroscopy](https://reader037.fdocuments.us/reader037/viewer/2022102808/55d204a7bb61eb7a438b472c/html5/thumbnails/79.jpg)
• When absorption intensity (ε) of a compound is decreased, it is known as hypochromic shift.
Naphthalene 2-methyl naphthaleneε = 19000 ε = 10250
CH3
• Hypochromic Effect4
![Page 80: U V Visible Spectroscopy](https://reader037.fdocuments.us/reader037/viewer/2022102808/55d204a7bb61eb7a438b472c/html5/thumbnails/80.jpg)
Wavelength ( λ )
Abso
rban
ce (
A )
Shifts and EffectsHyperchromic shift
Hypochromic shift
Redshift
Blueshift
λmax
![Page 81: U V Visible Spectroscopy](https://reader037.fdocuments.us/reader037/viewer/2022102808/55d204a7bb61eb7a438b472c/html5/thumbnails/81.jpg)
Solution too concentrated Diluted five-fold
![Page 82: U V Visible Spectroscopy](https://reader037.fdocuments.us/reader037/viewer/2022102808/55d204a7bb61eb7a438b472c/html5/thumbnails/82.jpg)
NH2
NO2
Solvent: Ethanol
Concentration: 15.4 mg L-1
Pathlength: 1 cm
UV-visible spectrum of 4-nitroanaline
![Page 83: U V Visible Spectroscopy](https://reader037.fdocuments.us/reader037/viewer/2022102808/55d204a7bb61eb7a438b472c/html5/thumbnails/83.jpg)
![Page 84: U V Visible Spectroscopy](https://reader037.fdocuments.us/reader037/viewer/2022102808/55d204a7bb61eb7a438b472c/html5/thumbnails/84.jpg)
![Page 85: U V Visible Spectroscopy](https://reader037.fdocuments.us/reader037/viewer/2022102808/55d204a7bb61eb7a438b472c/html5/thumbnails/85.jpg)
How does a spectrophotometer work.mp4
![Page 86: U V Visible Spectroscopy](https://reader037.fdocuments.us/reader037/viewer/2022102808/55d204a7bb61eb7a438b472c/html5/thumbnails/86.jpg)
UV Vis spectroscopy.mp4
![Page 87: U V Visible Spectroscopy](https://reader037.fdocuments.us/reader037/viewer/2022102808/55d204a7bb61eb7a438b472c/html5/thumbnails/87.jpg)
Advantages and disadvantages
![Page 88: U V Visible Spectroscopy](https://reader037.fdocuments.us/reader037/viewer/2022102808/55d204a7bb61eb7a438b472c/html5/thumbnails/88.jpg)
APPLICATIONS OF UV / VISIBLESPECTROSCOPY
![Page 89: U V Visible Spectroscopy](https://reader037.fdocuments.us/reader037/viewer/2022102808/55d204a7bb61eb7a438b472c/html5/thumbnails/89.jpg)
Applications• Qualitative & Quantitative Analysis:
– It is used for characterizing aromatic compounds and conjugated olefins.
– It can be used to find out molar concentration of the solute under study.
• Detection of impurities:– It is one of the important method to detect impurities in organic
solvents.• Detection of isomers are possible.• Determination of molecular weight using Beer’s law. • Detection of unknown compound.
![Page 90: U V Visible Spectroscopy](https://reader037.fdocuments.us/reader037/viewer/2022102808/55d204a7bb61eb7a438b472c/html5/thumbnails/90.jpg)
REFERENCES
![Page 91: U V Visible Spectroscopy](https://reader037.fdocuments.us/reader037/viewer/2022102808/55d204a7bb61eb7a438b472c/html5/thumbnails/91.jpg)
Reference Books
• Introduction to Spectroscopy– Donald A. Pavia
• Elementary Organic Spectroscopy– Y. R. Sharma
• Physical Chemistry– Puri, Sharma & Pathaniya
![Page 92: U V Visible Spectroscopy](https://reader037.fdocuments.us/reader037/viewer/2022102808/55d204a7bb61eb7a438b472c/html5/thumbnails/92.jpg)
Resources• http://www2.chemistry.msu.edu/faculty/reusch/Vir
tTxtJml/Spectrpy/UV-Vis/spectrum.htm
• http://en.wikipedia.org/wiki/Ultraviolet%E2%80%93visible_spectroscopy
• http://teaching.shu.ac.uk/hwb/chemistry/tutorials/molspec/uvvisab1.htm
![Page 93: U V Visible Spectroscopy](https://reader037.fdocuments.us/reader037/viewer/2022102808/55d204a7bb61eb7a438b472c/html5/thumbnails/93.jpg)
Thank You