Chemistry 341 spectroscopy lecture

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Chemistry 341 spectroscopy lecture

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Chemistry 341 Spectroscopy of Organic Compounds Modern Spectroscopic Methods  Revolutionized the study of Organic Chemistry  Determine the exact structure of small to medium size molecules in a few minutes  Nuclear Magnetic Resonance (NMR) and Infrared Spectroscopy (IR) are particularly powerful techniques which we will focus on Interaction of Light and Matter The Physical Basis of Spectroscopy  Quantum properties of light (photons)  Quantum properties of matter (quantized energy states)  Photons of light act as our “quantum probes” at the molecular level giving us back precise information about the energy levels within molecules The Electromagnetic Spectrum  Continuous  Covers a wide range of wavelengths of “light” from radio waves to gamma rays  Wavelengths (λ) range from more than ten meters to less than 10-12 meter The Electromagnetic Spectrum Relationship Between Wavelength, Frequency and Energy  Speed of light (c) is the same for all wavelengths  Frequency (ν), the number of wavelengths per second, is inversely proportional to wavelength: ν = c/λ  Energy of a photon is directly proportional to frequency and inversely proportional to wavelength: E = hν = hc/λ (where h = Plank’s constant) Wavelength/Spectroscopy Relationships Spectral Region Photon Energy Molecular Energy Changes UV-Visible ~ 100 kcal/mole Electronic Infrared (IR) ~ 10 kcal/mole Bond vibrations Radio < 0.1 kcal/mol Nuclear Spin states in a magnetic field Spin of Atomic Nuclei  Spin 1/2 atoms: mass number is odd examples: 1H and 13C  Spin atoms: mass number is even examples: 2H and 14N  Spin atoms: mass number is even examples: 12C and 16O Magnetic Properties of the Proton Related to Spin Energy States of Protons in a Magnetic Field ∆ E = λ absorbed light Applied Magnetic Field H ext IR Correlation Table Key Functional Groups by Region of the IR Spectrum IR Spectrum of Benzaldehyde IR Spectrum of Cyclohexanone IR Spectrum of Propanoic Acid Unknown A (Figure 14.27 Solomons 7th ed.)  Formula = C9H12  IHD =  IR shows no medium or strong bands above 1650 cm-1 except C-H stretching bands around 3,000 cm-1  HNMR δ: 1.26 (d, 6H), 2.90 (sept., 1H), 7.1-7.5 (m, 5H) Unknown B (Figure 14.27 Solomons 7th ed.)  Formula = C8H11N  IHD =  IR shows two medium peaks between 3300 and 3500 cm-1 No other medium or strong bands above 1650 cm-1 except C-H stretching bands around 3,000 cm-1  HNMR δ: 1.4 (d, 3H), 1.7 (s, br, 2H), 4.1(quart., 1H), 7.2-7.4 (m, 5H) Unknown C (Figure 14.27 Solomons 7th ed.)  Formula = C9 H10  IHD =  IR shows no medium or strong bands above 1650 cm-1 except C-H stretching bands around 3,000 cm-1  H NMR δ: 2.05 (pent., 2H), 2.90 (trip., 4H), 7.1-7.3 (m, 4H) Unknown H (Figure 9.48 Solomons 7th ed.)  Formula = C3H4Br2  IHD =  No IR data given  1HNMR δ: 4.20 (2H), 5.63 (1H), 6.03 (1H) Unknown Y (Figure 14.34 Solomons 7th ed.)  Formula = C9H12O  IHD =  IR shows a strong, broad, absorbance centered at 3400 cm-1  HNMR δ: 0.85 (t, 3H), 1.75 (m, 2H), 4.38 (s, br, 1H), 4.52 (t, 1H), 7.2-7.4 (m, 5H)

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Mục lục

  • Chemistry 341

  • Modern Spectroscopic Methods

  • Interaction of Light and Matter The Physical Basis of Spectroscopy

  • The Electromagnetic Spectrum

  • Slide 5

  • Relationship Between Wavelength, Frequency and Energy

  • Wavelength/Spectroscopy Relationships

  • Spin of Atomic Nuclei

  • Magnetic Properties of the Proton Related to Spin

  • Energy States of Protons in a Magnetic Field

  • Nuclear Magnetic Resonance (NMR)

  • The NMR Experiment

  • The NMR Spectrometer

  • Slide 14

  • The NMR Spectrum

  • Slide 16

  • Chemical Shift (d)

  • Shielding – The Reason for Chemical Shift Differences

  • Structure Effects on Shielding

  • Slide 20

  • Some Specific Structural Effects on NMR Chemical Shift

  • Spin-Spin Splitting

  • Spin-Spin Splitting Origin of the Doublet

  • Spin-Spin Splitting Origin of the Triplet

  • Spin-Spin Splitting Origin of the Quartet

  • Pascal’s Triangle

  • The n + 1 Rule

  • 1H NMR Spectrum of Bromoethane

  • 1H NMR Spectrum of 1-Nitropropane

  • Unknown A (Figure 9.20 Solomons 7th ed.)

  • Slide 31

  • Unknown B (Figure 9.20 Solomons 7th ed.)

  • Slide 33

  • Unknown C (Figure 9.20 Solomons 7th ed.)

  • Slide 35

  • Exceptions to the n+1 Rule

  • Slide 37

  • Slide 38

  • Slide 39

  • Slide 40

  • NMR: Some Specific Functional Group Characteristics

  • Slide 42

  • Slide 43

  • Slide 44

  • Slide 45

  • Slide 46

  • Slide 47

  • Slide 48

  • Slide 49

  • Infrared Spectroscopy

  • Slide 51

  • IR Spectrum of Ethanol

  • IR Correlation Table

  • Key Functional Groups by Region of the IR Spectrum

  • IR Spectrum of Benzaldehyde

  • IR Spectrum of Cyclohexanone

  • IR Spectrum of Propanoic Acid

  • Slide 58

  • Slide 59

  • Unknown A (Figure 14.27 Solomons 7th ed.)

  • Slide 61

  • Unknown B (Figure 14.27 Solomons 7th ed.)

  • Slide 63

  • Unknown C (Figure 14.27 Solomons 7th ed.)

  • Slide 65

  • Unknown H (Figure 9.48 Solomons 7th ed.)

  • Unknown Y (Figure 14.34 Solomons 7th ed.)

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