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NMR

NMR. Nuclear Magnetic Resonance. Chapter 13. Proton Nuclear Spin States. Magnetic Field. Two states have the same energy in the absence of a magnetic field. Protons in an external magnetic field. Energy difference between the spin-states depends on the strength of the magnetic field.

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NMR

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  1. NMR Nuclear Magnetic Resonance Chapter 13

  2. Proton Nuclear Spin States Magnetic Field Two states have the same energy in the absence of a magnetic field

  3. Protons in an external magnetic field Energy difference between the spin-states depends on the strength of the magnetic field.

  4. NMR Spectrometer

  5. Superconducting NMR Magnet

  6. NMR Sample Tubes

  7. NMR Probe Coils Sample goes in here Insulated tube

  8. Proton NMR Spectrum of Cl3CH NMR Signal Magnetic Field

  9. Field here less than Ho H Ho

  10. Electrons shield nucleus from external magnetic field. Magnetic field

  11. Energy to change spin state proportional to field strength E = H E =h Measure field strength in FREQUENCY units Cycles/second

  12. Tetramethylsilane TMS Reference compound for NMR spectrum.

  13. Cl3CH NMR signal 437 Hz at 60x106 Hz TMS Magnetic Field

  14. Chemical Shift Scale Position of Signal - Position of TMS x106 Chemical Shift = Spectrometer Frequency 437 Hz - 0 Hz x 106 = 7.28 ppm = 60x106Hz Units = parts per million = ppm

  15. Typical Chemical Shifts 0.9 - 1.8 2.7 - 4.1 2.1 - 2.5 3.3 - 3.7 3.1 - 4.1

  16. Typical Chemical Shifts 2.3 - 2.8 9 - 10 4.5 - 6.5 0.5 - 5 6.5 - 8.5

  17. Proton Chemical Shifts RH TMS 10 9 8 7 6 5 4 3 2 1 0 ppm down field from TMS

  18. Area proportional to number of protons

  19. How many lines would you expect in the proton NMR spectrum of this compound?

  20. Field from this proton can be aligned or opposed to applied field Measure signal from this proton Magnetic Field

  21. Spin Combinations - 2 adjacent protons -C-CH2- H 1 : 2 : 1

  22. Spin Combinations - 3 Adjacent Protons -C-CH3 H 1: 3: 3: 1

  23. Adjacent Protons Lines 1 2 3 2 3 4 • n + 1

  24. What is the name of this compound? • Ethyl Bromide

  25. What is this compound? CH3COCH2CH3

  26. What is this compound? • C6H5COCH3

  27. What is this compound? C6H5COOCH2CH3

  28. Magnetic field changes across sample y x

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