Proton NMR Spectroscopy

# Proton NMR Spectroscopy

## Proton NMR Spectroscopy

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##### Presentation Transcript

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. from chemistry.msu.edu

22. Methyl t-butyl ether (MTBE)

23. Toluene at Higher Field

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

25. Spin-Spin Splitting

26. The Doublet in 1H NMR

27. Hb in 1,1,2-Tribromoethane

28. The Triplet in 1H NMR

29. Ha in 1,1,2-Tribromoethane

30. 1,1,2-Tribromoethane

31. The Quartet in 1HMR

32. Predict Splitting

33. 1,1-Dichloroethane

34. Methyl Group appears as an Upfield Doublet

35. Methine H Appears as a Downfield Quartet

36. Ethyl benzene

37. Methyl Isopropyl Ketone

38. 1-Nitropropane

39. 2-Methyl-1-propanol

40. Para Nitrotoluene