UV spectoscopy by kailash vilegave

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UV spectoscopy,Woodwards-fieser rule Modern instrumentation of UV visible spectroscopy kailash vilegave

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Seminar on Ultra -Violet Spectroscopy:

1 Seminar on Ultra -Violet Spectroscopy Presented to: Dr.Veeresh S. Maddi Presented by: Kailash V. Vilegave K.L.E.s COP , Hubli -31 Dept: Pharmaceutics Dept Pharmaceutical chemistry K.L.E.s COP , Hubli -31 H.O.D. NKV

CONTENTS:

2 Woodwards-fieser rule Modern instrumentation of UV visible spectroscopy CONTENTS NKV

Absorption and Intensity Shifts:-:

3 Red shift :- λmax shifted towards longer wavelength Bathochromic shift. λ max shifted towards longer wavelength due to i) Presence of an auxochrome. ii) By change of solvent. Absorption and Intensity Shifts :- 200 nm 800 nm e Hypochromic Hypsochromic Hyperchromic Bathochromic NKV

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4 Benzen Aniline λ max -255nm λ max- 280 Here the NH 2 group is acts as a Auxochrome : Anilinium λ max 254nm But in anilinium there is no lone pair on nitrogen atom . No shairing take place. NKV

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5 Blue shifts: - λmax shifted towards shorter wavelength or hypsochromic shift or effect. due to i) removal of conjugation ii) by changing polarity of solvent. E.g. The aniline experienced a blue shift by removal of conjugation in acidic medium. Aniline λmax= 280nm Anilinium cation λmax = 253nm .. NKV

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6 Hyperchromic effect:- increases in the intensity of absorption maximum. i.e. Є max is increased. The introduction of auxochrome usually increases intensity of absorption Pyridine 2 methyl pyridine λmax= 257nm λmax = 262nm εmax = 2750 εmax = 3650 NKV

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7 Hypochromic effect :- decreases in the intensity of absorption maximum . i.e. Є max is decreased. 200 nm 800 nm e Hypochromic Hypsochromic Hyperchromic Bathochromic NKV Ex. Biphenyl 2methyle biphenyl Є max=19000 Є max= 10250 Distortion take place

Woodward-Fieser Rules:

8 Woodward- Fieser Rules NKV Woodward-Fieser rule is used to calculate the position of λ max for given structure ….. …..By relating the position of λ max with the position and degree of chromophores. # various types of double bond in a conjgugation describes below… Homoannular dienes Heteroannular dienes Endocyclic double bond Exocyclic double bond.

1) Homoannular dienes :

9 1) Homoannular dienes NKV It is cyclic dienes having conjugated double bond in a same ring. It is also called as homo dienes. Ex..

2) Heteroannular dienes :

10 2) Heteroannular dienes NKV It is cyclic dienese in which double bond in conjugation are present in different ring Ex..

3) Endocyclic double bond:

11 3) Endocyclic double bond NKV Double bond present in a ring Ex..

4) Exocyclic double bond. :

12 4) Exocyclic double bond. NKV It is double bond in which one of the double bonded atom is a part of a ring system Ex…

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13 NKV Endocyclic double bond Exocyclic double bond Ring A has one endocyclic and one exocyclic double bonds . While ring B has one endocyclic double bond only.

Woodward-Fieser Rules for Dienes , Trines ,polyenes etc. :

14 Woodward- Fieser Rules for Dienes , Trines , polyenes etc. NKV The constitutes the basic values or parent value . The constribution made by various alkyl substituents, ring residues, double bond extending conjugation and polar groups such as –Cl,-Br, -OR ,… ………are added to the basic value to obtain λ max for particular compound.

Woodward-Fieser Rules for Dienes:

15 Parent values: Heteroannular conjugated dienes ( transoid ) λ = 214 nm Acyclic transoid λ =217nm Homoannular conjugated dienes ( cisoid ) λ = 253 nm Increments for: Double bond extending conjugation 30 nm Alkyl substituent or ring residue 5 nm Exocyclic double bond  5 nm Auxochrome - OR 6 nm -SR 30 nm - Cl , -Br 5 nm -NR 2 60 nm Woodward-Fieser Rules for Dienes NKV

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16 NKV trans cis

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17 NKV

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18 nkv Woodward-Fieser Rules - Dienes For example:1 Isoprene – transoid acyclic butadiene = 217nm one alkyl subs. + 5 nm Calculated value 222nm Experimental value 220 nm

Woodward-Fieser Rules for Dienes:

19 Woodward- Fieser Rules for Dienes NKV Ex..2 Solution: A given compound is homoannular dienes which is having two alkyl substituents and two ring residue Parent value………………………………..253nm 2 Alkyl substituents ……………………….. 10nm 2 Ring residues …………………………… 10nm Calculated value………………………… 273nm Observed value…………………………… 265nm 1,4-dimethylcyclohex-13 diene

Woodward-Fieser Rules for Dienes:

20 Woodward- Fieser Rules for Dienes NKV Ex..3 Solution: The given compound is hetero annular dienes . It is having 4 ring residue as shown bellow. Parent value……………………………………..215nm 4 ring residue …………………………………… 20nm Calculated value……………………………….. 235nm Observed value………………………………… 236nm

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21 21 Woodward-Fieser Rules – Cyclic Dienes For example:4 1,2,3,7,8,8a-hexahydro-8a-methylnaphthalene heteroannular diene = 214 nm 3 alkyl subs. (3 x 5) +15 nm 1 exo C=C + 5 nm Calculated value 234 nm Experimental value 235 nm NKV

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22 Ex..5 Solution Basic value…………….. 217nm 2 alkyl subt. …………… 10nm 2 ring residue………….. 10nm 1 exocyclic double bond … 5nm Calculated value…………… 242nm Observed value…………….. 242nm NKV

Woodward-Fieser Rules for Dienes:

23 Woodward-Fieser Rules for Dienes Example…6 Acyclic transoid 217 nm Alkyl group or ring residue 3x5 = 15 nm Calculated 232 nm Observed 234 nm NKV

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24 NKV Cisoid : 253 nm Alkyl groups or ring residues: 2 x 5 = 10 nm Calculated: 263 nm Observed: 256 nm Example…7 Woodward-Fieser Rules for Dienes

Woodward-Fieser Rules for Dienes:

25 Woodward-Fieser Rules for Dienes Example..8 Transoid 214 nm Alkyl group or ring residue 3x5 = 15 nm Exocyclic double bond ( * ) 5 nm Calculated 234 nm Observed 235 nm NKV *

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26 NKV Cisoid: 253 nm Alkyl substituent ring residues: 3 x 5 = 5 nm 15 nm Exocyclic double bond( * ): 5 nm Calculated: 278 nm Observed: 275 nm Example…9 Woodward-Fieser Rules for Dienes *

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27 Base value 214nm Alkyl substitution 5*5 25nm Exocyclic double bond 5*3 15nm Extra conjugation 30nm Calculated 284nm Observed 283nm Woodward-Fieser Rules for Dienes Example…10

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28 Base value 214nm Alkyl substitution 5*4 20nm Exocyclic double bond 5 5nm Calculated 239nm Observed 238nm Woodward-Fieser Rules for Dienes Abetic acid Example…11

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29 Base value 214nm Alkyl substitution 5*5 25nm Exocyclic double bond 5*2 10nm Calculated 278nm Observed 281nm Woodward-Fieser Rules for Dienes Example…12 Neoabetic acid

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30 30 Woodward-Fieser Rules – Cyclic Dienes Be careful with your assignments – two common errors: This is not a heteroannular diene; you would use the base value for an acyclic diene Likewise, this is not a homooannular diene; you would use the base value for an acyclic diene λ max =232nm NKV

Woodward’s Rules for Conjugated Carbonyl Compounds:

31 Woodward’s Rules for Conjugated Carbonyl Compounds NKV Woodward fieser rule for calculating λ max for α – β unsaturated carbonyl compound modified by Scott.

Woodward’s Rules for Conjugated Carbonyl Compounds:

32 Woodward’s Rules for Conjugated Carbonyl Compounds Base values: X = R ( ketone ) α β unsaturated acyclic …. Six- membered ring or acyclic parent enone λ =215nm Five- membered ring parent enone λ =202nm X = H (aldehyde) λ =208nm X = OH (alcohol), OR (ester) λ =195nm NKV

Woodward’s Rules for Conjugated Carbonyl Compounds:

33 Increments for: Double bond extending conjugation 30 Exocyclic double bond 5 Endocyclic double bond in a 5- or 7-membered ring for X = OH, OR 5 Homocyclic diene component 39 Alkyl substituent or ring residue α 10 β 12 γ or higher 18 Woodward’s Rules for Conjugated Carbonyl Compounds NKV

Woodward’s Rules for Conjugated Carbonyl Compounds:

34 Polar groupings: - α β γ δ -OH 35  30 - 50 -OC(O)CH3   6  6 6 6 -OCH 3 35 30 17 31 -Cl 15  12 12 12 -Br 25 30 25 25 -NR 2 - 95 - - Woodward’s Rules for Conjugated Carbonyl Compounds NKV Auxochrome

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35 35 Group Increment 6-membered ring or acyclic enone Base 215 nm 5-membered ring parent enone Base 202 nm Acyclic dienone Base 245 nm Double bond extending conjugation 30 Alkyl group or ring residue a, b, g and higher 10, 12, 18 -OH a, b, g and higher 35, 30, 18 -OR a, b, g, d 35, 30, 17, 31 -O(C=O)R a, b, d 6 -Cl a, b 15, 12 -Br a, b 25, 30 -NR 2 b 95 Exocyclic double bond 5 Homocyclic diene component 39 NKV

Solvent shifts for various solvents: :

36 Solvent shifts for various solvents : NKV Solvent λ max shift (nm) water + 8 chloroform - 1 ether - 7 cyclohexane - 11 dioxane - 5 hexane - 11 In the compounds the actual spectra obtained are affected considerably by the nature of the solvent employed. Hence a solvent correction is applied to calculate value for that particular solvent

Woodward’s Rules for Conjugated Carbonyl Compounds:

37 Woodward’s Rules for Conjugated Carbonyl Compounds NKV β α Ex..1 Solution: The given compound is an α - β unsaturated acyclic ketone which is having alkyl substitution to α - position. Parent value………………………………….. 215nm 1 alkyl substituent at α - position……………... 10nm Calculated value……………………………… 225nm Observed value………………………………. 220nm

Woodward’s Rules for Conjugated Carbonyl Compounds:

38 Woodward’s Rules for Conjugated Carbonyl Compounds NKV Ex…2 The given compound has been α - β -unsaturated six membered ring structure ketone . It is having one ring residue at α - position and two at β - position and has double bonded exocyclic to two rings.

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39 NKV β α Parent value……………………………….. 215nm 1 ring residue at α -position ………………... 5nm 2 ring residue at β -position ………………. 24nm Double bond exocyclic to two rings………. 10nm Calculated value…………………………… 254nm Observed value……………………………. 256nm

Woodward’s Rules for Conjugated Carbonyl Compounds:

40 Acyclic enone:  215 nm α -Alkyl groups or ring residues:  10 nm β -Alkyl groups or ring residues: 2 x 12 = 24 nm Calculated:  249 nm Observed: 249 nm Woodward’s Rules for Conjugated Carbonyl Compounds NKV Ex…3

Woodward’s Rules for Conjugated Carbonyl Compounds:

41 Five-membered ring parent enone:  202 nm β -Alkyl groups or ring residues: 2 x 12 = 24 nm Exocyclic double bond: 5 nm Calculated: 231 nm Observed: 226 nm Woodward’s Rules for Conjugated Carbonyl Compounds NKV Ex…4 β α

Woodward’s Rules for Conjugated Carbonyl Compounds:

42 Five-membered ring parent enone:  202 nm α -Br:  25 nm β -Alkyl groups or ring residues:2 x 12 = 24 nm Exocyclic double bond: 5 nm Calculated:  256 nm Observed:  251 nm Woodward’s Rules for Conjugated Carbonyl Compounds NKV Ex…5 α β

Woodward’s Rules for Conjugated Carbonyl Compounds:

43 Woodward’s Rules for Conjugated Carbonyl Compounds NKV Ester: 195 nm β -Alkyl groups or ring residues: 12 nm Endocyclic double bond in 7-membered ring ( *) 5 nm Calculated: 212 nm Observed: 218 nm Ex…6 α β *

Woodward’s Rules for Conjugated Carbonyl Compounds:

44 Woodward’s Rules for Conjugated Carbonyl Compounds NKV Aldehyde : 208 nm α -Alkyl groups or ring residues: 10 nm β -Alkyl groups or ring residues: 2 x 12 = 24 nm Calculated: 242 nm Observed: 242 nm Ex…7 α β

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45 Basic value 215nm β alkul substitution 2*12 24nm Exocycliclated double bond 5nm Calculated 244nm Observed 241nm Ex…8

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46 Basic value 215nm β alkul substitution 2*12 24nm Exocycliclated double bond 5nm Calculated 244nm Observed 241nm Ex…9

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47 Basic value 215nm β alkyl substitution 1*12 12nm σ alkyl substitution 1*18 18nm Exocycliclated double bond 1*5 5nm Extra conjugation 1*30 30nm Calculated 280nm Observed 277nm Ex…10

Instrumentation:

48 Instrumentation NKV

SPECTROPHOTOMETER:

49 A spectrophotometer is a device which detects the percentage transmittance of light radiation when light of certain intensity & frequency range is passed through the sample. Thus the instrument compares the intensity of the transmitted light with that of the incident light. SPECTROPHOTOMETER NKV Transmittance, T = P / P0 % Transmittance, %T = 100 T

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50 These are expensive and more sophisticated and are designed to read % transmittance or absorbance, Record the absorption spectrum using plotter or recorder . These are of double beam type where we can use sample and reference solution at a time. Wavelength of accuracy is normally +/- 0.1nm . These instruments are hence more accurate & reliable than the other types. NKV Charecterestics of spectophotometer

Instrumentation:

51 Instruments for measuring the absorption of U.V. or visible radiation are made up of the following components; Sources (UV and visible ), Wavelength selector ( monochromators ), Detector, Recording system, Sample containers, Matched cell, Solvent. Instrumentation NKV

1) Sources of Light:

52 A) Hydrogen Discharge Lamp B) Deuterium Discharge Lamp C) Incandescent filament lamps D) Tungsten filament lamp E) Xenon Arc discharge lamp, F) Mercury Vapor Arc 1 ) Sources of Light NKV #Requirements - stable -constant intensity -Sufficient radiant energy #Basic

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53 A) HYDROGEN DISCHARGE LAMP: In these lamps hydrogen gas is stored under relatively high pressure. when an electric discharge is passed through the lamp, excited hydrogen molecules will be produced which emit UV radiations. These cover the range of 3500-1200 A. NKV

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54 3-5 times more intensity than other type. Measurement about 350 nm & near IR to 2.5um are usually made It gives continuous spectrum over the range Filament are usually coiled NKV

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55 C)TUNGSTEN LAMP: it is similar in its functioning to an electric bulb. The tungsten filament is heated electrically to white heat. To maintain the constant intensity ,the electrical current to the lamp must be carefully controlled. The lamps are generally stable & easy to use. NKV

D) XENON DISCHARGE LAMP:

56 In these ,xenon gas is stored under pressure in the range of 10-30 atmospheres. The xenon lamp possesses two tungsten electrodes separated by about 8mm. When an intense arc is formed between two tungsten electrodes by applying a low voltage, the UV light is produced. The intensity of UV radiation produced by xenon lamp is much greater than that of hydrogen lamp. D) XENON DISCHARGE LAMP NKV

E) Murcury Arc:

57 E) Murcury Arc If the mercury discharge lamp is enclosed in a glass tube, it is used to provide visible radiation. If the mercury discharge is fused in a silica envelope, it is used to provide U.V-radiation. It emits radiation in the range 350nm-800nm. NKV

2)MONOCHROMATORS:

58 PRISM - Refractive , Reflective GRATING – Transmission Grating Diffraction Grating 2 )MONOCHROMATORS NKV

FILTERS:

59 Absorption Filter Interference Filter FILTERS NKV Is a device , which allows light of required wavelength to pass through, but absorbs other wavelength wholly or partially Thus suitable filter can select desired wavelength band. Types of filters

Absorption Filter :

60 Absorption Filter Theory of complimentary colors. Color of the solution Complimentary colored filter Transmitted wavelength in nm Violet Yellowish Green 400-435 Blue Yellow 435-480 Greenish Blue orange 480-490 Bluish Green Red 490-500 Green Purple 500-560 Yellowish Green Violet 560-580 Yellow Blue 580-595 Orange Greenish Blue 595-610 Red Bluish Green 610-750 NKV

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61 Selection of absorption filter is done according to the following procedure: Write the color VIBGYOR in clockwise or anticlockwise manner, omitting Indigo. If solution to be analyzed is BLUE in color a filter having a complimentary color ORANGE is used in the analysis. NKV

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62 The color in the glass filters are produced by incorporating metal oxides like (V, Cr, Mn, Fe, Ni, Co, Cu etc.). Gelatin filter is prepared by adding organic pigments; Some natural organic pigments NKV

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63 NKV Some natural organic pigments

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64 NKV Some natural organic pigments

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65 NKV Some natural organic pigments

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66 Merits: Simple in construction, Cheaper, Selection of filter is easy. Demerits: Less accurate since there is a deviation of ±30nm, Intensity of radiation decreases due to absorption by filters. NKV

Interference Filter:

67 Interference Filter Interference filters are constructed by using two parallel glass plates which are silver coated internally. They are separated by a thin film of transparent dielectric spacer film made up of Calcium Fluoride (CaF 2 ) or Magnesium Fluoride (MgF 2 ) or Silicon oxide (Sio). NKV Works on the interference phenomenon, causes rejection of unwanted wavelength by selective reflection. These filters have a band pass of 10-15nm with peak transmittance of 40-60%.

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68 Merits: Inexpensive compared to prisms and gratings. More accurate compared to absorption filters. Demerits: One filter is used to provide only one specific wavelength. Therefore to cover the entire region of uv-visible region a number of filters are required NKV

Wavelength selector (monochromator) :

69 Constructions: All monochromators contain the following component parts; An entrance slit. A collimating lens. A dispersing device (usually a prism or a grating). A focusing lens. An exit slit. Wavelength selector (monochromator ) NKV

Monochromator:

70 Working:- Polychromatic radiation (radiation of more than one wavelength) enters the monochromator through the entrance slit. Monochromator NKV NKV

A dispersing device :

71 Rotating prism : made of glass, quartz or fused silica. Glass prims - used in visible range. Quartz and Fused silica prism – used in UV range. A dispersing device NKV

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72 NKV

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73 As a resolution of ±0.1nm can be achieved by using a grating, they are commonly used in a spectrometer. They are made up of glass , quartz or aluminum Gratings: NKV

They are of two types:

74 They are of two types a) Diffraction Gratings b) Transmission Gratings a ) Diffraction Gratings: NKV

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75 The mechanism is that diffraction produces reinforcement. The rays which are incident upon the grating get reinforced with the reflected rays and hence the resulting radiation has the wavelength which is governed by the equation: mλ = b (Sin i ± Sin r) λ = wavelength of radiation produced b = grating spacing i = angle of incidence r = angle of reflection m = order 0, 1, 2, 3 etc. NKV

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76 Czerney-Turner grating monochromator NKV

b)Transmission Gratings:   :

77 b )Transmission Gratings: It is similar to diffraction grating but refraction takes place instead of reflection. NKV λ = d Sin θ m where… λ = wavelength produced d = 1/lines per cm m = order 0, 1, 2, 3 etc. θ = angle of deflection Merits: Produces constant dispersion over the entire UV-visible region. Demerits: Difficult in construction.

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78 Comparison Prism Grating Made of Glass-: Visible Quartz/fused silica-: UV Alkali halide:-IR Grooved on highly polished surface like alumina. Working Principle Angle of Incident Law of diffraction mλ= d (sini±sinθ) Merits/demerits Prisms give non-liner dispersion hence no overlap of spectral order Grating gives liner dispersion hence overlap of spectral order. NKV

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79 Merits/ demerits Prisms are subjected to etching from atmospheric moisture. It can’t be used over considerable wavelength ranges. Prisms are not sturdy long lasting. Expensive Moisture resistant It can be used over considerable wavelength ranges. Grating are sturdy and long lasting. Economical. NKV Comparison Prism Grating

3)Detectors:

80 3)Detectors It is a component that converts EMR into an electron flow and subsequently into a current flow or voltage. NKV The types of detectors used in UV-visible spectroscopy are: a) Photo voltaic cell or barrier layer cell b) Photo tubes or photo emissive cells c) Photo multiplier tubes d) Silicon diode.

a).Photo voltaic cells or barrier layer cells:   :

81 a). Photo voltaic cells or barrier layer cells: NKV

b).Photo tubes or Photo emissive cells:   :

82 b). Photo tubes or Photo emissive cells: NKV

c)Photo multiplier tubes: :

83 c )Photo multiplier tubes: These are the most sensitive of all the detectors, expensive and used in sophisticated instruments. The principle involves multiplication of photoelectrons by secondary emission of electrons. This is achieved by using a photo cathode and a series of anodes (dynodes), up to 10 dynodes are used. NKV

Each dynode is maintained at 75-100 volts higher than the preceding one. .At each stage the electron emission is multiplied by a factor 4 or 5 due to secondary emission of electrons.  :

84 Each dynode is maintained at 75-100 volts higher than the preceding one. .At each stage the electron emission is multiplied by a factor 4 or 5 due to secondary emission of electrons. Cross section of a photomultiplier tube NKV

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85 NKV

D. Thermal detectors : :

86 D. Thermal detectors : sensitive to IR ( λ >750 nm) Thermocouple s - junction thermometer Bolometers - resistance thermometer Pyroelectric devices - piezoelectric effect NKV

4) Sample cell:

87 4) Sample cell Sample cell or cuvettes are used to hold a sample solution. For visible radiation the sample cells are made up of glass and for the UV the cells are made up of quartz, since glass absorbs UV radiations. The path length of sample cell ranges from 1cm to 10cm. Sample cells may be rectangular or cylindrical in shape. The material of the sample cell should not absorb at the wavelength observed NKV

5) Recording system:

88 5) Recording system The signals from the detector finally received by the recording system The recording is done by recorder pen In this DC current signals are produce that are amplified by DC amplifier & read on analog meter, recorders, digital voltmeter, display of computer system NKV

6) Matched cells:

89 6) Matched cells When double beam instrumentation is used two cell are needed one for the reference and one for the sample It normal for absorption and can lead to analytical error For most accurate work matched cells are used “ these are cells in which absorption of each one is equal to or very nearly equal to absorption of other those within very similar absorptivities are put together and designed matched cell .” NKV

7) Solvents:

90 7) Solvents Solvents must be transparent in the region to be observed; the wavelength where a solvent is no longer transparent is referred to as the cutoff Common solvents and cutoffs: acetonitrile …………………… 190 chloroform……………………. . 240 cyclohexane …………… ... 195 1,4-dioxane………. ……….. 215 95% ethanol…….. ………… 205 n-hexane ………………… 201 methanol …………………….. 205 isooctane ……………………… 195 water …………………….. 190 NKV

Power supply:

91 Power supply A power supply serves a triple function It decreases line voltage to the instrument operating level with a transformer It converts AC to DC with a rectifier if direct current is required by Instrument . It smooth out in line voltage in order to deliver a constant voltage to source lamp and instrument. NKV

U.V. Spectroscopic Instruments:

92 U.V. Spectroscopic Instruments NKV

Types of U.V. Spectroscopic Instruments :

93 Types of U.V. Spectroscopic Instruments A) Single beam spectrophotometer B) Double beam spectrophotometer NKV

A) Single-beam Spectrophotometer :

94 A) Single-beam Spectrophotometer The measurement of % transmittance with a manual single beam instrument involves three steps: 0% transmittance adjustment 100% transmittance adjustment Determination of % of sample NKV

Disadvantages:

95 Disadvantages NKV It measures total amount of light reaching the detector rather the percentage absorbed Light may lost at reflecting surface or may be absorbed by solvent used to dissolve the sample. Response of detector varies significantly with wavelength of the reading falling on it . So this problems of instrument variation can be largely overcome by using double beam system

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96 reference 200 700 l , nm monochromator/ beam splitter optics UV-VIS sources sample Detector I 0 I 0 I 0 I log(I 0 /I) = A Double-Beam Spectrometer NKV

Double beam spectrophotometer:

97 The radiation from the source is allowed to pass via a mirror system to the monochromator unit. The radiation coming out of the monochromator through the exit slit is received by rotating sector which divides the beam into two beams, one passing through the reference & the other through the sample cell. After passing through the sample & reference cells, the light beams are focused onto the detector. Double beam spectrophotometer NKV

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98 The output of the detector is connected to a phase sensitive amplifier which responds to any change in transmission through sample & reference. The phase sensitive amplifier transmits the signals to the recorder which is followed by the movement of the pen on chart. NKV

Advantages of double beam Spectrophotometer:

99 Advantages of double beam Spectrophotometer 1)It is not necessary to continuously replace the blank with the sample or adjust to zero for each sample as in single beam instruments. 2)The ratio of the intensities of the sample and reference beams is constantly obtained. 3)Any error due to variation in intensity of the source or fluctuation in the detector is minimized. 4)Rapid scanning over a wide λ region. NKV

COMPARISON::

100 COMPARISON: SL. NO SINGLE BEAM INSTRUMENT DOUBL BEAM INSTRUMENT 1. 2. Calibration should be done with blank every time, before measuring the absorbance or transmittance of sample Radiant energy intensity changes with fluctuation of voltage. Calibration is done only in the beginning It permits a large degree of inherent compensation for fluctuations in the intensity of the radiant energy.

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101 3 4 5 6 In single beam it’s not possible to compare blank and sample together. It measure the total amount of transmitted light reaching the detector In single beam radiant energy wavelength has to be adjusted every time Working on single beam is tedious and time consuming. In double beam it’s possible to do direct one step comparison of sample in one path with a standard in the other path. It measures the percentage of light absorbed by the sample In this scanning can be done over a wide wavelength region Working on double beam is fast and non tedious.

Reference: -:

102 Willard Merritt and Dean“Instrumental Method of Analysis” 7 th edition. Pavia “Introduction to spectoscopy” 3 rd edition William Kemp, “Organic Spectroscopy” 3rd edition . Sharma Y.R., “Elementary Organic Spectroscopy” 3rd edition. Chatwal and Anand, “Instrumental Method of Chemical Analysis”, 13th edition. Spectroscopy of organic compounds by p. S.Kalsi Internet source. ( www.chemistry.ccsu.edu/glagovich/ teaching/316/uvvis/uvvis.html. www.shu.ac.uk/schools/sci/ chem/tutorials/molspec/lumin3.html ) Reference: - NKV

thaNK you !!!:

103 thaNK you !!! All the Best for exam NKV

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104 Basic value 215nm β alkul substitution 2*12 24nm Exocycliclated double bond 5nm Calculated 244nm Observed 241nm

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105

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106

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107 Base value 214nm Alkyl substitution 5*3 15nm Exocyclic double bond 5nm Homoannular 39nm Calculated 273nm Observed 275nm Woodward-Fieser Rules for Dienes

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108 Base value 214nm Alkyl substitution 5*4 20nm Exocyclic double bond 5*2 5nm Homoannular 39nm Calculated 278nm Observed 281nm Woodward-Fieser Rules for Dienes

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109 Base value 214nm Alkyl substitution 5*5 25nm Homoannular 39nm Calculated 268nm Observed 272nm Woodward-Fieser Rules for Dienes

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