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Ir spectroscopy sud mpharm pdf

  1. 1. INFRARED SPECTROSCOPY By Sudheerkumar Kamarapu pharmaceutical analysisSri Shivani College of Pharmacy
  3. 3. Classification of analytical techniques1.Separation techniques →Chromatography2.Spectrophotometric → SPECTROSCOPY3. Electro analytical → Potentiometry,conductometry4. Titrimetric analysis→ Titrations
  4. 4. Spectroscopy “seeing the unseeable”.Spectroscopy is the branch of science deals with the study of interaction of electromagnetic radiation with matter.Electromagnetic radiation is a type of energy that is transmitted through space at enormous velocities. EMR→ANALYTE→SPECTROPHOTOGRAPH ↓ concentration should be lower
  5. 5. Using electromagnetic radiation as a probe to obtain information about atoms and molecules that are too small to see.Electromagnetic radiation is propagated at the speed of light through a vacuum as an oscillating wave.
  6. 6. electromagnetic relationships: λυ = c λ 1/υ E = hυ E υ E = hc/λ E 1/λ λ = wave length υ = frequency c = speed of light λ E = kinetic energy c h = Planck’s constant
  7. 7. Two oscillators will strongly interact when their energies are equal. E1 = E2 λ1 = λ2 υ1 = υ2If the energies are different, they will not strongly interact!We can use electromagnetic radiation to probe atoms and molecules tofind what energies they contain.
  8. 8. some electromagnetic radiation ranges Approx. freq. range Approx. wavelengths Hz (cycle/sec) metersRadio waves 104 - 1012 3x104 - 3x10-4Infrared (heat) 1011 - 3.8x1014 3x10-3 - 8x10-7Visible light 3.8x1014 - 7.5x1014 8x10-7 - 4x10-7Ultraviolet 7.5x1014 - 3x1017 4x10-7 - 10-9X rays 3x1017 - 3x1019 10-9 - 10-11Gamma rays > 3x1019 < 10-11
  9. 9. IR SPECTROSCOPY INTRODUCTION Infrared spectroscopy (IR) measures the bond vibration frequencies in a molecule and is used to determine the functional groups. The infrared region of the spectrum encompasses radiation with wave numbers ranging from about 12,500 to 50cm-1 (or) wave lengths from 0.8 to 200µ. Infrared region lies between visible and microwave region.
  10. 10. The infrared region constitutes 3 partsa) The near IR (0.8 -2.5µm) (12,500-4000cm-1)b) The middle IR (2.5 -15µm) (4000-667cm-1) i) Group frequency Region (4000-1500cm-1) ii) Finger print Region (1500-667cm-1)c) The far IR (15-200µm) (667-50cm-1) most of the analytical applications are confined to the middle IR regionbecause absorption of organic molecules are high in this region.Wave number is mostly used measure in IR absorption because wavenumbers are larger values & easy to handle than wave length which aremeasured in µm. E = hν = hc/λ = hcν¯It gives sufficient information about the structure of a compound.
  11. 11. PRINCIPLE In any molecule it is known that atoms or groups of atoms are connected by bonds. These bonds are analogous to springs and not rigid in nature. Because of the continuous motion of the molecule they maintain some vibrations with some frequency characteristic to every portion of the molecule. This is called the natural frequency of vibration. When energy in the form of infrared radiation is applied and when,Applied infrared frequency= Natural frequency of vibration
  12. 12. MOLECULAR VIBRATIONSThere are 2 types of vibrations.1) Stretching vibrations2) Bending vibrations• 1)Stretching vibrations: in this bond length is altered.• They are of 2 types• a) symmetrical stretching: 2 bonds increase or decrease in length.
  13. 13. b) Asymmetrical stretching: in this one bond length isincreased and other is decreased.2)Bending vibrations:•These are also called as deformations.•In this bond angle is altered.•These are of 2 types•a) in plane bending→ scissoring, rocking•b) out plane bending→ wagging, twisting
  14. 14. Scissoring:This is an in plane bending.In this bond angles are decreased.2 atoms approach each other.Rocking:•In this movement of atoms takes place in same direction.
  15. 15. Wagging:It is an out of plane bending.In this 2 atoms move to one side of the plane. They move up and down theplane.Twisting:•In this one atom moves above the plane and the other atom moves belowthe plane.
  16. 16. NUMBER OF VIBRATIONAL MODES A molecule can vibrate in many ways, and each way is called a vibrational mode. If a molecule contains ‘N’ atoms, total number of vibrational modes For linear molecule it is (3N-5) For non linear molecule it is (3N-6)Eg: H2O, a non-linear molecule, will have 3 × 3 – 6 = 3degrees of vibrational freedom, or modes.
  17. 17. VIBRATIONAL FREQUENCY occurs when atoms in a molecule are in periodic motion while the molecule as a whole has constant translational and rotational motion. The frequency of the periodic motion is known as a vibration frequency. The value of stretching vibrational frequency of a bond can be calculated by the application of hooke’s law. ν/c = ν¯ = 1/2пc[k/m1m2/m1+m2]1/2 = 1/2пc√k/µWhere, µ→reduced mass m1&m2 →masses of the atoms k →force constant c →velocity of radiation
  18. 18. Factors influencing vibrational frequencies Calculated value of frequency of absorption for a particular bond is never exactly equal to its experimental value. There are many factors which are responsible for vibrational shifts1) Vibrational coupling:• it is observed in compounds containing –CH2 & -CH3. EG. Carboxylic acid anhydrides amides aldehydes
  19. 19. 2) Hydrogen bonding: Hydrogen bonding brings about remarkable downward frequency shifts. Stronger the hydrogen bonding, greater is the absorption shift towards lower wave length than the normal value. There is 2 types of hydrogen bonding a) inter molecular→broad bands b) intra molecular → sharp bands•hydrogen bonding in O-H and N-H compounds deserve specialattention.•Eg: alcohols&phenols enols & chelates
  20. 20. 3) Electronic effects:In this the frequency shifts are due to electronic effectswhich include conjugation, mesomeric effect, inductiveeffect.a) conjugation: conjugation lowers the absorptionfrequency of C=O stretching whether the conjugation isdue to α,β- unsaturation or due to an aromatic ring.b) mesomeric effect: a molecule can be represented by2or more structures that differ only in the arrangement ofelectrons.c) inductive effect: depends upon the intrinsic tendencyof a substituent to either release or withdraw electrons.
  21. 21. TYPES OF INSTRUMENTATIONThere are 2 types of infrared spectrophotometer, characterized by the manner in which the ir frequencies are handled.1) dispersive type (IR)2) interferometric type(FTIR) In dispersive type the infrared light is separated intoindividual frequencies by dispersion, using a gratingmonochromator. In interferometric type the ir frequencies areallowed to interact to produce an interference pattern andthis pattern is then analyzed, to determine individualfrequencies and their intensities.
  22. 22. DISPERSIVE INSTRUMENTS These are often double-beam recording instruments, employing diffraction gratings for dispersion of radiation. These 2 beams are reflected to a chopper which consists of rotating mirror. It sends individual frequencies to the detector thermopile. Detector will receive alternately an intense beam & a weak beam. This alternate current flows from detector to amplifier.
  24. 24.  It is used to produce a new signal of a much lower frequency which contains the same information as the original IR signal. The output from the interferometer is an interferogram. Radiation leaves the source and is split. Half is reflected to a stationary mirror and then back to the splitter. The other half of the radiation from the source passes through the splitter and is reflected back by a movable mirror. Therefore, the path length of this beam is variable. The two reflected beams recombine at the splitter, and they interfere . interference alternates between constructive and destructive phases. The accuracy of this measurement system means that the IR frequency scale is accurate and precise.
  25. 25. FOURIER TRANSFORM IR SPECTROMETER In the FT-IR instrument, the sample is placed between the output of the interferometer and the detector. The sample absorbs radiation of particular wavelengths. An interferogram of a reference is needed to obtain the spectrum of the sample. After an interferogram has been collected, a computer performs a Fast Fourier Transform, which results in a frequency domain trace (i.e intensity vs wavenumber). The detector used in an FT-IR instrument must respond quickly because intensity changes are rapid . Pyroelectric detectors or liquid nitrogen cooled photon detectors must be used. Thermal detectors are too slow. To achieve a good signal to noise ratio, many interferograms are obtained and then averaged. This can be done in less time than it would take a dispersive instrument to record one scan.
  26. 26. Advantages of Fourier transform IR over dispersive IRImproved frequency resolutionImproved frequency reproducibility (older dispersive instruments must be recalibrated for each session of use)Faster operationComputer based (allowing storage of spectra and facilities for processing spectra)Easily adapted for remote use (such as diverting the beam to pass through an external cell and detector, as in GC - FT-IR)
  27. 27.  Opaque or cloudy samples Energy limiting accessories such as diffuse reflectance or FT-IR microscopes High resolution experiments (as high as 0.001 cm -1 resolution) Trace analysis of raw materials or finished products Depth profiling and microscopic mapping of samples Kinetics reactions on the microsecond time-scale Analysis of chromatographic and thermogravimetric sample fractions
  28. 28. Comparison Beetween Dispersion Spectrometer and FTIR To separate IR light, a grating is used. Detector Dispersion Grating Slit Spectrometer In order to measure an IR spectrum, the dispersion Spectrometer takes Sample several minutes. Also the detector receives only a few % of the energy of original light source. To select the specified IR light, Light source A slit is used. Fixed CCM An interferogram is first made by the interferometer using IR FTIR light. In order to measure an IR spectrum, Detector FTIR takes only a few seconds. Moreover, the detector receives up to 50% of the energy of original B.S. light source. (much larger than the dispersion spectrometer.) SampleMoving CCM The interferogram is calculated and transformed IR Light source into a spectrum using a Fourier Transform (FT).
  29. 29. FTIR seminar FT Optical System Diagram Light He-Ne gas lasersource(ceramic) Beam splitter Movable mirror Sample chamber (DLATGS) Fixed mirror Detector Interferometer
  30. 30. Applications of Infrared AnalysisPharmaceutical researchForensic investigationsPolymer analysisLubricant formulation and fuel additivesFoods researchQuality assurance and controlEnvironmental and water quality analysis methodsBiochemical and biomedical researchCoatings and surfactantsEtc.
  31. 31. PARTS OF INSTRUMENTATION• I R Radiation Source Monochromators – Incandescent lamp – Nernst Glower – Globar Source – Mercury Arc • Detectors• Sample Cells & Sampling – Bolometers Substances – Thermocouple – Sampling of solids – Thermistors • Solids run solution – Golay Cells • Solid films – Photoconductivity cell • Mull technique • Pressed pellet technique – Semiconductor – Pyroelectric detectors – Sampling of Liquids – Sampling of Gases2/5/2013 sudheerkumar kamarapu 32
  32. 32. I R Radiation Sources Incandescent Lamps• ordinary lamp used• glass enclosedDisadv.• fails in far infrared• low spectral emissivity2/5/2013 sudheerkumar kamarapu 33
  33. 33. Nernst GlowerComposed of rare earth oxides such as Zirconia, Yttria & Thoria Non conducting at room temperature WORKING Heating Conducting state Provides radiation of about 7100 cm-1Disadv. Emitts I R radiation over wide wavelength range Frequent mechanical failure Energy concentrated in visible & near I R region of spectrum 2/5/2013 sudheerkumar kamarapu 34
  34. 34. Globar Source• Self starting, Controlled conveniently with variable transformer Works at wavelength longer than 650 cm-1 (0.15µ)5200 cm-1 radiation given at 1300 – 1700 OCDisadv.Less intense source than Nernst Glower2/5/2013 sudheerkumar kamarapu 35
  35. 35. Mercury ArcSpecial high pressure mercury lamps are used in far I RBeckman devised the Quartz Mercury Lamps in unique manner shorter wavelength ------- heated quartz envelope provides radiation longer wavelength -------- mercury plasma provides radiation2/5/2013 sudheerkumar kamarapu 36
  36. 36. MONOCHROMATORS• They convert polychromatic light into mono chromatic light.• They must be constructed of materials which transmit the IR.• They are of 3 types.• a) metal halide prisms• b) NaCl prisms• c) gratings2/5/2013 sudheerkumar kamarapu 37
  37. 37.  a) metal halide prisms:• prisms which are made up of KBr are used in the wavelength region from 12-25µm.• LiF prisms are used in the wavelength region from 0.2-6µm.• CeBr prisms used in wavelength region from 15-38µm. b) NaCl prisms:• Used in the whole wave length region from 4000- 650cm-1.• they have to be protected above 20•c because of hygroscopic nature. c) gratings:• They offer better resolution at low frequency than prisms. 382/5/2013 sudheerkumar kamarapu
  38. 38. • Sample cells made up of alkali halides like NaCl or KBr are used.• Aqueous solvents cannot be used as they dissolve alkali halides.• Only organic solvents like chloroform is used.• IR spectroscopy has been used for the characterization of solid, liquid, gas samples.2/5/2013 sudheerkumar kamarapu 39
  39. 39. Solids run in solution Solids dissolved in a aqueous solvent Placed over the alkali metal disk Solvent is allowed to evaporate Thin film of solute formed Entire solution is run in one of the cells for liquidsNote :This method not used because suitable number of solvents available are less.Absorption due to solvent has to be compensated by keeping the solvent in a cell of same thickness as that containing the reference beam of2/5/2013 double beam spectrometer.sudheerkumar kamarapu 40
  40. 40. Solid Films• Technique used for Amorphous sample.• Deposited on the KBr / NaCl cell by evaporation of solution.• Only useful for rapid qualitative analysis. Mull Technique• Finely ground solid sample is used.• Mixed with Nujol (mineral oil)• Thick paste is made.• Spread between I R transmitting windows• Mounted in path of I R beam &• The spectrum is run.Disadv. Nujol has the absorption maxima at 2915, 1462, 1376 & 719 cm-12/5/2013 sudheerkumar kamarapu 41
  41. 41. Pressed Pellet Technique• Finely ground sample used• Potassium Bromide is mixed (100 times more)• Passed through a high pressure press• Small pellet formed (1-2 mm thick, 2cm diameter)• The pellet is transparent to I R radiation & is run as suchAdv.• Pellet can be stored for long period of times.• Concentration of sample can be adjusted in KBr pellet hence used for quantitative analysis.• Resolution of spectrum is superior.Disadv.• Always has a band at 3450 cm-1 (moisture OH-)• At high pressure polymorphic changes occur•2/5/2013 Unsuccessful for polymersudheerkumar kamarapu which are difficult to grind with KBr. 42
  42. 42. Diffuse Reflectance• Sometimes referred to as DRIFTS (diffuse reflectance infrared Fourier transform spectroscopy)• Involves irradiation of the powdered sample by an infrared beam.• The incident radiation undergoes absorption, reflection, and diffraction by the particles of the sample.• Only the incident radiation that undergoes diffuse reflectance contains absorptivity information about the sample.2/5/2013 sudheerkumar kamarapu 43
  43. 43. Microspectroscopy• The ultimate sampling technique, since only one particle is required for analysis.• Particles of interest must be greater in size than 10 X 10 μm.• Sample placed on an IR optical window and the slide is placed onto the microscope stage and visually inspected• Once the sample of interest is in focus, the field of view is apertured down to the sample.• Depending on sample morphology, thickness, and transmittance properties, a reflectance and/or transmittance IR spectrum may be acquired by the IR microscope accessory.2/5/2013 sudheerkumar kamarapu 44
  44. 44. Attenuated Total Reflectance• The basic premise of the technique involves placing the sample in contact with an infrared transmitting crystal with a high refractive index.• The infrared beam is directed through the crystal, penetrating the surface of the sample, and displaying spectral information of that surface.• Advantage of this technique is that it requires very little sample preparation,• Simply place the sample in contact with the crystal2/5/2013 sudheerkumar kamarapu 45
  45. 45. Photoacoustic• The PAS phenomenon involves the selective absorption of modulated IR radiation by the sample.• Once absorbed, the IR radiation is converted to heat and subsequently escapes from the solid sample and heats a boundary layer of gas.• The increase in temperature produces pressure changes in the surrounding gas.• The pressure changes in the coupling gas occur at the frequency of the modulated light, as well as the acoustic wave.• This acoustical wave is detected by a very sensitive microphone and the subsequent electrical signal is Fourier processed and a spectrum produced.2/5/2013 sudheerkumar kamarapu 46
  46. 46. • Liquid samples taken.• Put it into rectangular cells of KBr, NaCl etc.• I R spectra obtained.• Sample thickness … such that transmittance lies between 15 – 20 % i.e., 0.015 – 0.05 mm in thickness.• For double beam, matched cells are generally employed• One cell contains sample while other has solvent used in sample.• Matched cells should be of same thickness, protect from moisture.2/5/2013 sudheerkumar kamarapu 47
  47. 47. • Small size particles hence the cells are large.• 10 cm to 1m long• Multiple reflections can be used to make the effective path length as long as 40 cm• Lacks sensitivity2/5/2013 sudheerkumar kamarapu 48
  48. 48. DETECTORS They convert the radiation into electrical signal. Two Types Of DetectorsThermal Detectors Photon Detectors Thermocouple  Semiconductors Bolometers  Photovoltaic Intrinsic Thermistors Detectors Golay Detectors  Photoconductive Pyroelectric Detectors Intrinsic Detectors 2/5/2013 sudheerkumar kamarapu 49
  49. 49. ThermocouplesBased upon the fact that an electrical current will flow when two dissimilar metal wires are connected together at both ends and a temperature differential exists between the two endsExample : Bismuth & Antimony2/5/2013 sudheerkumar kamarapu 50
  50. 50. Bolometer• It consists of thin metallic conductor, its resistance changes due to increase in temperature when IR radiation falls on it.• It is a electrical resistance thermometer which can detect and measure feeble thermal radiation.• The electrical resistance increases approx 0.4% for every celsius degree increase of temperature .• The degree of change in resistance is regarded as the measure of the amount of IR radiation falling on it.• A bolometer is made of two platium strips, covered with lamp black, one strip is sheilded from radiation and one exposed to it. The strips formed two branches of wheatstone bridge2/5/2013 sudheerkumar kamarapu 51
  51. 51. Working – The circuit thus effectively operating as resistancetemperature detector. When IR radiations falling on the exposedstrip would heat it, and change the resistance, this causes currentto flow, the amount of current flowing is a measure of intensity ofIR radiationThe response time is 4 secs.2/5/2013 sudheerkumar kamarapu 52
  52. 52. Golay Cells• It consist of a small metal detector closed by a rigid blackened metal plate (2 mm), flexible silvered diaphragm at the other end filled with Xenon gas.• Its response time is 20 msec, hence faster than other thermal detectors• It is suitable for wavelengths greater then 15 u2/5/2013 sudheerkumar kamarapu 53
  53. 53. Working• The radiation falls on the blackened metal plate, this heats the gas which lead to deformation of flexible silvered diaphragm.• The light from a lamp inside the detector is made to fall on the diaphragm which reflects the light on to a phototube.• The signal seen by the phototube / photocell is modulated in accordance with the power of the radiation beams incident on the gas cell. 2/5/2013 sudheerkumar kamarapu 54
  54. 54. Thermistors• It is made up of metal oxides.• It functions by changing resistance when heated.• It consists of two closely placed thermistor flakes, one of the 10 um is an active detector, while the other acts as the compensating / reference detector.• A steady voltage is applied, due to the temperature increase there is change in resistance which is measured and this gives the intensity of the IR radiation2/5/2013 sudheerkumar kamarapu 55
  55. 55. Pyroelectric Detectors• It consist of a thin dielectric flake on the face of which an electrostatic charge appears. When the temperature of the flake changes upon exposure to IR radiations, electrodes attached to the flake collect the charge creating a voltage.• The most common is TGS (Triglycine Sulfate) however its response deteriorates above 45 C and is lost above the 49 C• Detureated triglycine Sulfated are available and can be used at room temperature.2/5/2013 sudheerkumar kamarapu 56
  56. 56. PHOTON DETECTORS• These detectors convert photons directly into free current carriers by photo exciting electrons across the energy band gap of the semiconductor to the conduction band. This produces a resistance change in the detectors.• This photon excitation is caused by radiation interacting directly with the lattice sites.2/5/2013 sudheerkumar kamarapu 57
  57. 57. Semiconductors• These act as insulators but when radiation fall on them, they become conductors.• Exposure to radiation causes a rapid response to the IR signal.• Working – An IR photon displaces an electron in the detector which excites electrons to move from the valence band to the higher energy conduction band.• Semiconductor materials are Telluride, Indium, Antimonide & Germanium. 2/5/2013 sudheerkumar kamarapu 58
  58. 58. Photovoltaic intrinsic detectors• Under IR radiation, the potential barrier of the P N junction leads to the photovoltaic effect. An incident photon with the energy greater the energy band gap of the junction generates electron hole pairs and the photocurrent is excited.• The amount of the photon excited current is denoted by photocurrent.• The highest performance PV detectors are fabricated from Si, Ge, As, In & Sb. 2/5/2013 sudheerkumar kamarapu 59
  59. 59. Photoconductive Intrinsic Detectors• This is non thermal detector of greater sensitivity.• It consists of a thin layer of lead sulfide supported on gas envelope. When IR radiation is focused on the lead sulfide its conductance increases and causes more current to flow.• It has high sensitivity and good speed of about 0.5 msec• Upon drastic cooling the range can be broadened.• PC detectors include Germanium and Silicon detectors. 2/5/2013 sudheerkumar kamarapu 60
  60. 60. COMPARISON2/5/2013 sudheerkumar kamarapu 61
  61. 61. Identification of organic and inorganic compounds by IR Spectroscopy (Interpretation of Spectra)2/5/2013 sudheerkumar kamarapu 62
  62. 62. IR source  sample  prism  detector graph of % transmission vs. frequency => IR spectrum 100 %T 0 4000 3000 2000 1500 1000 500 v (cm-1)2/5/2013 sudheerkumar kamarapu 63
  63. 63. toluene2/5/2013 sudheerkumar kamarapu 64
  64. 64. Intensity in IRIntensity: Transmittance (T) or %T I T= I0 Absorbance (A) I A = log I0IR : Plot of %IR that passes through a sample (transmittance) vs Wavelenght 2/5/2013 sudheerkumar kamarapu 65
  65. 65. Infrared • Position, Intensity and Shape of bands gives clues on Structure of molecules • Modern IR uses Michelson Interferometer => involves computer, and Fourier Transform Sampling => plates, polished windows, Films … Must be transparent in IRNaCl, KCl : Cheap, easy to polish NaCl transparent to 4000 - 650 cm-1 KCl transparent to 4000 - 500 cm-1 KBr transparent to 400 cm-1 2/5/2013 sudheerkumar kamarapu 66
  66. 66. Infrared: Low frequency spectra of window materials2/5/2013 sudheerkumar kamarapu 67
  67. 67. Bond length and strength vs Stretching frequency Bond C-H =C-H -C-H Length 1.08 1.10 1.12 Strenght 506 kJ 444 kJ 422 kJ IR freq. 3300 cm-1 3100 cm-1 2900 cm-12/5/2013 sudheerkumar kamarapu 68
  68. 68. Calculating stretching frequenciesHooke’s law : n : Frequency in cm -1n 1  = K c : Velocity of light => 3 * 1010 cm/s 2pc m K : Force constant => dynes /cm m:masses of atoms in grams m1 m2 M1 M2 m= = m1 + m2 M1 + M2 (6.02 * 1023)n = 4.12  K m C—C K = 5* 105 dynes/cm C=C K = 10* 105 dynes/cm CC K = 15* 105 dynes/cm 2/5/2013 sudheerkumar kamarapu 69
  69. 69. Calculating stretching frequenciesC=C K = 10* 105 dynes/cm n = 4.12  K m n= 4.12 M1 M2 (12)(12)m= M1 + M2 = 12 + 12 =6  10* 105 6 = 1682 cm-1 n Experimental  1650 cm-1C—H K = 5* 105 dynes/cm n= 4.12  5* 105 .923 = 3032 cm-1 M1 M2 (12)(1)m= = =0.923 n M1 + M2 12 + 1 Experimental  3000 cm-1C—D K = 5* 105 dynes/cm n= 4.12  5* 105 .923 = 2228 cm-1 M1 M2 (12)(2)m= = =1.71 n M1 + M2 12 + 2 Experimental  2206 cm-1 2/5/2013 sudheerkumar kamarapu 70
  70. 70. Vibrations Stretching frequency Bending frequency OModes of vibration Bending C H Stretching C—H H H H Wagging Scissoring H H 1350 cm-1 1450 cm-1 H H H H H H Symmetrical Asymmetrical Rocking Twisting 2853 cm-1 720 cm-1 1250 cm-1 2926 cm-1 H 2/5/2013 sudheerkumar kamarapu 71
  71. 71. VibrationsGeneral trends:•Stretching frequencies are higher than bending frequencies (it is easier to bend a bond than stretching or compresing them)•Bond involving Hydrogen are higher in freq. than with heavier atoms•Triple bond have higher freq than double bond which has higher freq than single bond 2/5/2013 sudheerkumar kamarapu 72
  72. 72. Structural Information from Vibration Spectra The symmetry of a molecule determines the number of bands expectedNumber of bands can be used to decide on symmetry of a moleculeTha task of assignment is complicated by presence of low intensity bands andpresence of forbidden overtone and combination bands.There are different levels at which information from IR can be analyzed to allowidentification of samples: • Spectrum can be treated as finger print to recognize the product of a reaction as a known compound. (require access to a file of standard spectra) • At another extreme , different bands observed can be used to deduce the symmetry of the molecule and force constants corresponding to vibrations. • At intermediate levels, deductions may be drawn about the presence/absence of specific groups 2/5/2013 sudheerkumar kamarapu 73
  73. 73. Methods of analyzing an IR spectrum The effect of isotopic substitution on the observed spectrum Can give valuable information about the atoms involved in a particular vibration1. Comparison with standard spectra : traditional approach2. Detection and Identification of impurities if the compound have been characterized before, any bands that are not found in the pure sample can be assigned to the impurity (provided that the 2 spectrum are recorded with identical conditions: Phase, Temperature, Concentration)3. Quantitative Analysis of mixture Transmittance spectra = I/I0 x 100 => peak height is not lineraly related to intensity of absorption In Absorbance A=ln (Io/I) sudheerkumar=> Direct measure of intensity 74 2/5/2013 kamarapu
  74. 74. Analyzing an IR spectrumIn practice, there are similarities between frequencies of molecules containing similar groups.Group - frequency correlations have been extensively developed for organic compounds andsome have also been developed for inorganics 2/5/2013 sudheerkumar kamarapu 75
  75. 75. Some characteristic infrared absorption frequenciesBOND COMPOUND TYPE FREQUENCY RANGE, cm-1C-H alkanes 2850-2960 and 1350-1470 alkenes 3020-3080 (m) and RCH=CH2 910-920 and 990-1000 R2C=CH2 880-900 cis-RCH=CHR 675-730 (v) trans-RCH=CHR 965-975 aromatic rings 3000-3100 (m) and monosubst. 690-710 and 730-770 ortho-disubst. 735-770 meta-disubst. 690-710 and 750-810 (m) para-disubst. 810-840 (m) alkynes 3300O-H alcohols or phenols 3200-3640 (b)C=C alkenes 1640-1680 (v) aromatic rings 1500 and 1600 (v)C≡C alkynes 2100-2260 (v)C-O primary alcohols 1050 (b) secondary alcohols 1100 (b) tertiary alcohols 1150 (b) phenols 1230 (b) alkyl ethers 1060-1150 aryl ethers 1200-1275(b) and 1020-1075 (m) 2/5/2013 sudheerkumar kamarapu 76all abs. strong unless marked: m, moderate; v, variable; b, broad
  76. 76. IR spectra of ALKANES C—H bond ―saturated‖ (sp3) 2850-2960 cm-1 + 1350-1470 cm-1 -CH2- + 1430-1470 -CH3 + ― and 1375 -CH(CH3)2 + ― and 1370, 1385 -C(CH3)3 + ― and 1370(s), 1395 (m)2/5/2013 sudheerkumar kamarapu 77
  77. 77. n-pentane 2850-2960 cm-1 3000 cm-1 sat’d C-H 1470 &1375 cm-1 CH3CH2CH2CH2CH32/5/2013 sudheerkumar kamarapu 78
  78. 78. n-hexane CH3CH2CH2CH2CH2CH32/5/2013 sudheerkumar kamarapu 79
  79. 79. 2-methylbutane (isopentane)2/5/2013 sudheerkumar kamarapu 80
  80. 80. 2,3-dimethylbutane2/5/2013 sudheerkumar kamarapu 81
  81. 81. cyclohexane no 1375 cm-1 no –CH32/5/2013 sudheerkumar kamarapu 82
  82. 82. IR of ALKENES =C—H bond, ―unsaturated‖ vinyl (sp2) 3020-3080 cm-1 + 675-1000 RCH=CH2 + 910-920 & 990-1000 R2C=CH2 + 880-900 cis-RCH=CHR + 675-730 (v) trans-RCH=CHR + 965-975 C=C bond 1640-1680 cm-1 (v)2/5/2013 sudheerkumar kamarapu 83
  83. 83. 1-decene unsat’d C-H 3020- 3080 cm-1 910-920 & C=C 1640-1680 990-1000 RCH=CH22/5/2013 sudheerkumar kamarapu 84
  84. 84. 4-methyl-1-pentene 910-920 & 990-1000 RCH=CH22/5/2013 sudheerkumar kamarapu 85
  85. 85. 2-methyl-1-butene 880-900 R2C=CH22/5/2013 sudheerkumar kamarapu 86
  86. 86. 2,3-dimethyl-1-butene 880-900 R2C=CH22/5/2013 sudheerkumar kamarapu 87
  87. 87. IR spectra BENZENEs =C—H bond, ―unsaturated‖ ―aryl‖ (sp2) 3000-3100 cm-1 + 690-840 mono-substituted + 690-710, 730-770 ortho-disubstituted + 735-770 meta-disubstituted + 690-710, 750-810(m) para-disubstituted + 810-840(m) C=C bond 1500, 1600 cm-12/5/2013 sudheerkumar kamarapu 88
  88. 88. ethylbenzene 3000- 3100 cm-1 Unsat’d 1500 & 1600 C-H 690-710, Benzene ring 730-770 mono-2/5/2013 sudheerkumar kamarapu 89
  89. 89. o-xylene 735-770 ortho2/5/2013 sudheerkumar kamarapu 90
  90. 90. p-xylene 810-840(m) para2/5/2013 sudheerkumar kamarapu 91
  91. 91. m-xylene meta 690-710, 750-810(m)2/5/2013 sudheerkumar kamarapu 92
  92. 92. styrene no sat’d C-H 1640 C=C 910-920 & 990-1000 mono RCH=CH22/5/2013 sudheerkumar kamarapu 93
  93. 93. 2-phenylpropene Sat’d C-H 880-900 mono R2C=CH22/5/2013 sudheerkumar kamarapu 94
  94. 94. p-methylstyrene para2/5/2013 sudheerkumar kamarapu 95
  95. 95. IR spectra ALCOHOLS & ETHERS C—O bond 1050-1275 (b) cm-1 1o ROH 1050 2o ROH 1100 3o ROH 1150 ethers 1060-1150 O—H bond 3200-3640 (b) 2/5/2013 sudheerkumar kamarapu 96
  96. 96. 1-butanol 3200-3640 (b) O-H C-O 1o CH3CH2CH2CH2-OH2/5/2013 sudheerkumar kamarapu 97
  97. 97. 2-butanol O-H C-O 2o2/5/2013 sudheerkumar kamarapu 98
  98. 98. tert-butyl alcohol O-H C-O 3o2/5/2013 sudheerkumar kamarapu 99
  99. 99. methyl n-propyl ether no O--H C-O ether2/5/2013 sudheerkumar kamarapu 100
  100. 100. 2-butanone  C=O ~1700 (s)2/5/2013 sudheerkumar kamarapu 101
  101. 101. C9H12 1500 & 1600 benzene C-H unsat’d & mono sat’d C9H12 – C6H5 = -C3H7 isopropylbenzene n-propylbenzene?2/5/2013 sudheerkumar kamarapu 102
  102. 102. n-propylbenzene2/5/2013 sudheerkumar kamarapu 103
  103. 103. isopropylbenzene isopropyl split 1370 + 13852/5/2013 sudheerkumar kamarapu 104
  104. 104. C8H6 C-H 1500, 1600 unsat’d benzene 3300 C 8 H6 – C 6 H5 = C 2 H C-H mono phenylacetylene2/5/2013 sudheerkumar kamarapu 105
  105. 105. C4H8 Unst’d 1640- 880-900 1680 R2C=CH2 C=C isobutylene CH3 CH3C=CH22/5/2013 sudheerkumar kamarapu 106
  106. 106. Which compound is this? a) 2-pentanone 1-pentanol b) 1-pentanol c) 1-bromopentane d) 2-methylpentane2/5/2013 sudheerkumar kamarapu 107
  107. 107. What is the compound? a) 1-bromopentane 2-pentanone b) 1-pentanol c) 2-pentanone2/5/2013 2-methylpentane d) sudheerkumar kamarapu 108
  108. 108. 2/5/2013 sudheerkumar kamarapu 109
  109. 109. In a ―matching‖ problem, do not try to fully analyze each spectrum. Look for differences in the possible compounds that will show up in an infrared spectrum. H2 H2 H2 A C C C CH2 E C C H biphenyl allylbenzene 1,2-diphenylethane CH3 CH3 D CH3CH2CH2CH2CH3 F CH2CH2CH2CH3 B o-xylene n-pentane n-butylbenzene2/5/2013 sudheerkumar kamarapu 110
  110. 110. 12/5/2013 sudheerkumar kamarapu 111
  111. 111. 22/5/2013 sudheerkumar kamarapu 112
  112. 112. 32/5/2013 sudheerkumar kamarapu 113
  113. 113. 42/5/2013 sudheerkumar kamarapu 114
  114. 114. 52/5/2013 sudheerkumar kamarapu 115
  115. 115. 62/5/2013 sudheerkumar kamarapu 116
  116. 116. References :Lena Ohannesian, Antony J. Streeter; Handbook of Pharmaceutical Analysis; Marcel Dekker, Inc.; Reprint 2002Chatwal and Anand ; Instrumental methods of chemical analysis; fifth edition; page no-2.43-46Spectrometric identification of organic compounds, R M Silverstein,T.C morril G.C. bassler Fifth edition, 2/5/2013 sudheerkumar kamarapu 117
  117. 117. 2/5/2013 sudheerkumar kamarapu 118