Dnyanasadhana College, Thane. Department of Chemistry T. Y. B. Sc Dnyanasadhana College, Thane. Department of Chemistry T.Y.B.Sc. Analytical Chemistry Paper-IV Sem-V UV-Visible spectroscopy dr.g.r.bhgaure

T.Y.B.Sc. Syllabus Double beam photometer Single Beam Spectrophotometer Double Beam Spectrophotometer Qualitative Analysis Quantitative Analysis

Energy Increases Wavelength Decreases Electromagnetic Spectrum

In this energy is supplied by photons. Sources of Energy In this energy is supplied by photons. Absorption Spectroscopy Scattering Techniques

Thermal or chemical energy source . Sources of Energy Thermal or chemical energy source . Emission Spectroscopy luminescence spectroscopy

Electromagnetic spectrum Radiation Source H2 and D2 lamp Wavelength region continuum source from 160–380 nm Useful for UV molecular absorption UV Spectroscopy

Electromagnetic spectrum Radiation Source Tungsten lamp Wavelength region 400-800 nm Useful for Vis molecular absorption Visible Spectroscopy

Light get reflected back Scattering of Light Transmission of light 0.003 Absorbance Light get reflected back

Regions of Absorption U.V. 200-400 nm Visible 400-800 nm

INSTRUMENT Colorimeter OR Photometer 400-800 nm Spectrophotometer 200-800 nm.

DOUBLE BEAM PHOTOMETER Sample Cuvette Photocell Colour Filter Collimating Lens Mirror Radiation Source Blank Cuvette Reference Photocell C 100 A J1 Galvanometer J2 B D

SINGLE BEAM SPECTROPHOTOMETER Radiation Source Collimating Lense SINGLE BEAM SPECTROPHOTOMETER O.2 Read out Meter Amplifier PMT Detector Sample Cuvette Grating

DOUBLE BEAM SPECTROPHOTOMETER PMT Detector Blank Cuvette Mirror Grating Tungsten Lamp Read Out Meter Mirror Sample Cuvette Mirror Deuterium Lamp PMT Detector DOUBLE BEAM SPECTROPHOTOMETER

Distinguish Between Photometer and Spectrophotometer Radiation source is Tungsten filament lamp. Absorbance of light is measured in the wavelength 400-800 nm.( Visible region) Filters are used to select monochromatic light. Sample cells made from glass. Detectors used are photocell or photoemmisive tube. Absorbance of coloured solution is measured SPECTROPHOTOMETER. Radiation source is Hydrogen or deuterium lamp. Absorbance of light is measured in the wavelength 200--800 nm. (U.V.& Visible region) Prism or Gratings are used to select monochromatic light. Sample cells made from quartz. Detectors used are photomultiplier tube. Absorbance of coloured as well as colorless solution can be measured

LIGHT DISPERSING DEVICES MONOCHROMATORS SPECTROPHOTOMETERS FILTERS (COLORIMETERS ) MONOCHROMATORS SPECTROPHOTOMETERS

Filter: A filter transmits the monochromatic beam of light and absorbs other light Polychromatic light Monochromatic light

FOCUSING LENS COLLIMATING LENS PRISM ENTRANCE SLIT EXIT SLIT LAMBDA-1 LAMBDA-2 PRISM ENTRANCE SLIT EXIT SLIT PRISM MONOCHROMATOR

MAGINIFIED VIEW ENLARGED VIEW GRATING MONOCHROMATOR

Applications of U.V. & Visible Spectroscopy Qualitative Analysis Identification of Structural Groups in Molecules. Spectroscopic analysis of a substance is carried out using radiation of a particular wavelength this wave length is called as Lambda Max. The Constituent groups in a molecule absorbed to their characteristic wavelengths. It is possible to determine a particular group in a molecule by determining its Lambda Max. Lambda Max values of important groups are given in following table.

A B S O N C E Wavelength --- 200 300 400 500 600 700 800 The Wavelength at which absorbance of highly concentrated solution is maximum is called as Lambda max. A B S O N C E Lambda Max 200 300 400 500 600 700 800 Wavelength ---

Orbital's containing electrons are called as Bonding Orbital's Types of Orbital's Bonding Orbital's : Orbital's containing electrons are called as Bonding Orbital's Antibonding Orbital's vacant or unounoccupied Orbital's ( Not containing electrons) are called as anti Bonding Orbital's .

Closed shell electrons Covalent single bonded electrons Types of Electrons in a molecule Closed shell electrons Not absorbing / Not in bonding Covalent single bonded electrons σ Sigma Electrons in π orbital's Paired nonbonding outershell electrons n electrons C---C Sigma bond σ Sigma electrons C==C C C H—O---H

The three include transitions involving ELECTRONIC TRANSITIONS There are three types of electronic transitions. The three include transitions involving 1) , , and n electrons (Organic Molecule) 2) d and f electrons (Inorganic molecule) 3) Charge transfer electrons.(Org+Inorgainc)

ELECTRONIC TRANSITIONS , , and n electrons d and f electrons charge transfer electrons Organic Molecule Inorganic molecule Organic + Inorganic

Energy levels for Electronic transitions in a Molecule * Antibonding * Antibonding ∏ n *  * n *  * n Nonbonding  Bonding Energy  Bonding

Example Functional Groups Lambda Max ( nm) Solvents Acetic Acid --COOH 208 Ethyl Alcohol Acetyl Chloride --COCl 220 Hexane Acetamide --CONH2 178 Nitromethane --NO2 201 Methyl Alcohol Azomethane --N=N-- 338 Acetaldehyde >C=O 290 Acetone 189

B) Chromopores and Auxochromes: Chromopores are unsaturated groups responsible for the absorption of visible light.e.g. >C=O (carbonyl group). The molecule which contain Chromopores are called as chromogen and the colour of the compound is due to unsaturated groups present in Chromopore. The intensity of the colour of the chromogen increases with the number of chromophores present. For ex.ethylene (CH2= CH2) is colorless but CH3-( CH= CH)6--CH3 is yellow. As the number of groups increase in a molecule absorption shifts to longer wavelength and the colour deepens.

Example Functional Groups Lambda Max ( nm) Solvents Ethylene >C=C< 171 Vapour Acetaldehyde >C=C 290 Hexane Acetic Acid --COOH 208 Ethyl Alcohol Nitromethane --NO2 201 Napthalene Unsaturated comp. 275 Methyl Vinyl Ketone 215 Cinnamic Acid

Applications of U.V. & Visible Spectroscopy Quantitative Analysis By Calibration Curve Method

Other Applications UV and visible spectroscopy can be used up to concentrations up to 10-6 and some times up to 10-7 M . Qualitative analysis can be performed because each absorbing species absorb at different wave length. It used in water and air pollution studies. It is also used to study the complexes and in the determination of complex. It is used in industry to monitor various process controls. It is also used to study to distinguish between cis-and trans isomerism. C- is isomer absorbs at shorter wave length and trans isomer absorb at longer wave length.

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