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2. 2 Requirements for Spectroscopic Techniques for Polymers 1. High resolution 2. High sensitivity (>1%) 3. High selectivity between molecular structures 4. Capable of examining sample in use-state 5. Nondestructive and non-invasive 6. Can vary temperature and environment of sample 7. Fast turnaround time

3. 3 Useful Web site for fundamentals: www.organicworldwide.net Useful Spectroscopic Techniques High Resolution NMR of Polymer Solutions (Samples are dissolved) Mass Spectrometry (Samples are vaporized) Highly Useful Spectroscopic Techniques FT-IR spectroscopy Raman Spectroscopy High Resolution Solid State NMR UV and Visible Spectroscopy (insufficient resolution) Spectroscopic Techniques Which are Sometimes Useful

4. Each technique is based upon a unique phenomenon: Each technique is based upon a unique phenomenon: Infrared spectroscopy; vibrational energy absorption Infrared spectroscopy; vibrational energy absorption Raman spectroscopy: inelastic scattering from vibrational Raman spectroscopy: inelastic scattering from vibrational levels levels NMR: nuclear energy absorption while the sample is located in a magnetic field NMR: nuclear energy absorption while the sample is located in a magnetic field Mass spectrometry: ionization Mass spectrometry: ionization One technique may be better suited than another for a particular problem One technique may be better suited than another for a particular problem It is important to know the limitations of each technique i.e., sample preparation, etc. It is important to know the limitations of each technique i.e., sample preparation, etc. 4

5. 5 Characteristics Sensitive to polar groups and antisymmetric modes Small amounts of samples needed (mg, as low as ng) Signal detection is simple Special sample preparation is often needed (thin films, KBr pellets ….) Infrared Spectroscopy

6. 6 Raman Spectroscopy Characteristics Sensitive to nonpolar groups and symmetric modes Inefficient detection scheme (1 photon out of a million) Special site-specific techniques available resonance Raman spectroscopy surface enhanced Raman spectroscopy Sampling method is often simple Highly focused laser beam

7. 7 NMR Spectroscopy Characteristics Solution NMR Signal intensity can be directly and quantitatively related to chemical group concentration Sensitive to molecular mobility Sensitive to surrounding electronic environment Sensitivity depends on the nucleus of interest (natural abundance and magnetogyric ratio) Some nuclei show little signal overlap

8. 8 NMR Spectroscopy Characteristics Solid-state NMR In addition to the characteristics in solution-state NMR …. Can study frozen solid state conformation Ability to determine the position of proton Ability to determine the correlation among nuclei

9. 9 Mass Spectrometry Characteristics Very sensitive (amount of detectable sample, pg and fg) Ability to determine precise mass of a molecular fragment or mother molecule (MALDI) or mother molecule (MALDI) Needs to be vaporized and ionized (fragmentation) Various sampling and ionization techniques

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17.  Amplitude Maximum height of the oscillating stuff 17

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36.  E (Molecules or Atoms)= Transition + Electronic + Vibration + Rotation 36 Quantized Energy levels Uv-Visb frequencies (200-400 nm) IR frequencies (2.5 -15  m, 400 – 4000 (cm -1 ) Microwave frequencies (1 – 10 -3 m)

37. Electronic and Vibration energy levels 37

38. Energy possessed by molecules is quantised. When a molecule interacts with radiation there can be changes in electronic, vibrational or rotational energy. These changes depend on the frequency of the radiation. Analysis of the energy needed to change from one energy level to another forms basis of molecular spectroscopy. 38

39. Substances exposed to radiation from frequency range 10 14 Hz to 10 13 Hz (wavelengths 2.5μm - 15μm) Causing vibrational energy changes in the molecule These absorb infrared radiation of specific frequencies. Point is to identify functional groups in the molecule 39

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41.  SIMPLE diatomic molecules can only vibrate one way, by stretching. 41 H Br For these molecules there is only one vibrational infrared absorption.

42.  More complex molecules have more possible deformations 42 OCO symmetric stretch

43. 43 OCO OCO asymmetric stretch

44. 44 OCO

45. 45 O C O

46. 46 O C O

47. 47 O C O

48. 48 OCO

49. 49 O C O

50. 50 O C O

51. 51 O C O bending

52. 52 c = λ f from this equation we can get the reciprocal of the wavelength ( 1 / λ ) this is a direct measure of the frequency

53. 53 wavenumber ( 1/λ) / cm -1 wavelength ( λ) / μm frequency (v) / Hz 1000200030004000 10 2.5 2.5 x 10 13 1.0 x 10 14

54.  Sample placed in ir spectrometer  Subjected to ir radiation  Molecule absorbs energy  Molecule bonds starts to undergo different types of vibration (stretching, bending etc.)  This produces different signals that the detector records as ‘peaks’ on the spectrum. 54

55.  Frequencies are different for each molecule  Energy required for vibration depends on strength of bond  Weaker bonds requiring less energy. 55

56. Important … When an ir spectrum is obtained we do not try to explain the whole thing, simply look for one or two signals that are characteristic of different bonds. 56

57. O-H bond stretch C-H bond stretch C-O bond stretch 57

58. O CC H H H H H H O-H bond stretch 3670 cm -1 C-O bond stretch 1050 cm -1 C-H bond stretch 3010 -2850 cm -1 58

59.  Usually match a particular bond to a particular absorption region.  The precise position of the peak depends on the bond environment, so only wavenumber regions can be quoted. 59

60.  The strongest (more intense) absorptions occur when a large change in bond polarity associated with the vibration.  e.g. C=O bonds will give more intense absorptions than C=C bonds. 60

61. Below 1500cm -1 the IR spectrum can be quite complex This region is characteristic of a particular molecule Hence known as ‘fingerprint region’ Absorption range / cm -1 Bonds responsibleExamples 4000-2500Single bonds to HO-H, C-H, N-H 2500-2000Triple bonds C ≡ C, C ≡ N 2000-1500Double bondsC=C, C=O Below 1500variousC-O, C-X 61