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Proton NMR Spectroscopy

Proton NMR Spectroscopy. The NMR Phenomenon. Most nuclei possess an intrinsic angular momentum , P . Any spinning charged particle generates a magnetic field. P = [I(I+1)] 1/2 h/2 p where I = spin quantum # I = 0, 1/2, 1, 3/2, 2, …. Which nuclei have a “spin”?.

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Proton NMR Spectroscopy

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  1. Proton NMR Spectroscopy

  2. The NMR Phenomenon • Most nuclei possess an intrinsic angular momentum, P. • Any spinning charged particle generates a magnetic field. P = [I(I+1)]1/2 h/2p where I = spin quantum # I= 0, 1/2, 1, 3/2, 2, …

  3. Which nuclei have a “spin”? • If mass # and atomic # are both even, I = 0 and the nucleus has no spin. e.g. Carbon-12, Oxygen-16 • For each nucleus with a spin, the # of allowed spin states can be quantized: • For a nucleus with I, there are 2I + 1 allowed spin states. 1H, 13C, 19F, 31Pall have I = 1/2 DE = g(h/2p)Bo

  4. Spin states split in the presence of B0

  5. When a nucleus aligned with a magnetic field, B0, absorbs radiation frequency (Rf), it can change spin orientation to a higher energy spin state. By relaxing back to the parallel (+1/2) spin state, the nucleus is said to be in resonance. Hence, NMR

  6. Presence of Magnetic Field

  7. NMR instruments typically have a constant Rf and a variable B0. A proton should absorb Rf of 60 MHz in a field of 14,093 Gauss (1.4093 T). Each unique probe nucleus (1H perhaps) will come into resonance at a slightly different - and a very small percentage of - the Rf. All protons come into resonance between0 and 12/1,000,000 (0 – 12 ppm) of the Rf.

  8. Energy Difference (E) Between Two Different Spin States of a Nucleus With I=1/2

  9. What Does an NMR Spectrum Tell You? • # of chemically unique H’s in the molecule # of signals • The types of H’s that are present e.g. aromatic, vinyl, aldehyde … chemical shift • The number of each chemically unique H integration • The H’s proximity to eachother spin-spin splitting

  10. How many signals in the Proton NMR Spectrum?

  11. Chemical EquivalenceHow many signals in 1H NMR spectrum?

  12. Number of Equivalent Protons

  13. Vinyl Protons

  14. Typical 1H NMR Scale is 0-10 ppm

  15. The d Scale

  16. Tetramethylsilane (TMS)

  17. Chemical Shift Ranges, ppm

  18. Diamagnetic AnisotropyShielding and Deshielding

  19. Deshielding in Alkenes

  20. Shielding in Alkynes

  21. Chemical Shift is Affected by Electron Density Around Nucleus

  22. from chemistry.msu.edu

  23. Methyl t-butyl ether (MTBE)

  24. Toluene at Higher Field

  25. Integral TraceHow many protons give rise to each signal?

  26. Spin-Spin Splitting

  27. The Doublet in 1H NMR

  28. Hb in 1,1,2-Tribromoethane

  29. The Triplet in 1H NMR

  30. Ha in 1,1,2-Tribromoethane

  31. 1,1,2-Tribromoethane

  32. The Quartet in 1HMR

  33. Predict Splitting

  34. 1,1-Dichloroethane

  35. Methyl Group appears as an Upfield Doublet

  36. Methine H Appears as a Downfield Quartet

  37. Ethyl benzene

  38. Methyl Isopropyl Ketone

  39. 1-Nitropropane

  40. 2-Methyl-1-propanol

  41. Para Nitrotoluene

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