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/2  where  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. 1 H, 13 C, 19 F, 31 P all have I = 1/2  E =  h/2  )Bo

4. Spin states split in the presence of B 0

5. When a nucleus aligned with a magnetic field, B 0, 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 B 0. A proton should absorb Rf of 60 MHz in a field of 14,093 Gauss (1.4093 T). Each unique probe nucleus ( 1 H perhaps) will come into resonance at a slightly different - and a very small percentage of - the Rf. All protons come into resonance between 0 and 12/1,000,000 (0 – 12 ppm) of the B 0.

8. Nuclei aligned with the magnetic field are lower in energy than those aligned against the field The nuclei aligned with the magnetic field can be flipped to align against it if the right amount of energy is added (DE) The amount of energy required depends on the strength of the external magnetic field

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

10. 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

11. Chemical Equivalence How many signals in 1 H NMR spectrum?

12. Number of Equivalent Protons

13. Homotopic H’s –Homotopic Hydrogens Hydrogens are chemically equivalent or homotopic if replacing each one in turn by the same group would lead to an identical compound

14. Enantiotopic H’s If replacement of each of two hydrogens by some group leads to enantiomers, those hydrogens are enantiotopic

15. Diastereotopic H’s If replacement of each of two hydrogens by some group leads to diastereomers, the hydrogens are diastereotopic –Diastereotopic hydrogens have different chemical shifts and will give different signals

16. Vinyl Protons

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

24. The  Scale

25. Tetramethylsilane (TMS)

26. Chemical Shift Ranges, ppm

28. Diamagnetic Anisotropy Shielding and Deshielding

29. Deshielding in Alkenes

30. Shielding in Alkynes

33. Methyl t-butyl ether (MTBE)

34. Toluene at Higher Field Splitting patterns in aromatic groups can be confusing A monosubstituted aromatic ring can appear as an apparent singlet or a complex pattern of peaks

35. Integral Trace

36. Spin-Spin Splitting

37. The Doublet in 1 H NMR

38. H b in 1,1,2-Tribromoethane

39. The Triplet in 1 H NMR

40. H a in 1,1,2-Tribromoethane

41. 1,1,2-Tribromoethane

42. The Quartet in 1 HMR

43. 1,1-Dichloroethane

44. Ethyl benzene

45. CH 3 CH 2 OCH 3

46. Equivalent Protons do not Couple

47. Pascal’s Triangle

48. Methyl Isopropyl Ketone

49. 1-Nitropropane

50. Differentiate using 1 H NMR

51. Coupling Constants (J values)

52. Para Nitrotoluene

53. Bromoethane

54. para-Methoxypropiophenone

55. Styrene

56. H a splitting in Styrene “Tree” Diagram

57. In the system below, Hb is split by two different sets of hydrogens : Ha and Hc –Theortically Hb could be split into a triplet of quartets (12 peaks) but this complexity is rarely seen in aliphatic systems

60. C-13 NMR Spectroscopy

61. C-13 chemical shifts

62. Methyl Propanoate C-13 proton decoupled

63. Ethyl Acrylate; C-13 prediction

64. Ethyl Acrylate; C-13 NMR

65. Coupling in C-13 NMR

68. Butanone - Coupled and Decoupled

69. 1,2,2-Trichloropropane 1 H and 13 C NMR Spectra

70. Coupled C-13 NMR Spectrum