1. Electromagnetic Spectrum

2. PROTON NUCLEAR MAGNETIC RESONANCE ( 1 H NMR)

3. The 1 H NMR Spectrum. Absorbance of energy by a proton via NMR results in flipping of its nuclear spin state. Both 1 H and 13 C have spin numbers of I = ½. The number of allowed spin states is = 2(I) + 1. Both 16 O, 12 C and 2 H (deuterium) have spin numbers of zero and are NMR inactive. The spinning nucleus generates a small magnetic field. When placed in an external magnetic field (B o ) it will align either with or against B o. The energy needed to flip spin states is in the radiofrequency region (resonance energy) and is proportional to the field strength, B o.

4. Radiofrequency and B o (H o )

5. The 1 H NMR Spectrum. The resonance energy of a given H is affected by the electron density around that H. The applied field causes es to circulate around H which induces a field opposing B o thus the nucleus does not feel the full effect of B o. The nuclei of those Hs having a greater electron density are said to be shielded from B o and those with less e-density are deshielded. Resonance energy is a frequency and is reported in cps = Hz or ppm = .

6. Terms used in an NMR spectrum. Downfield Upfield Less shielding More shielding Low induced field High induced field Larger  Smaller  300 Hz ppm =  = -------------- = 5  or 5 ppm 60 MHz  values

7. Information from the 1H NMR Spectrum. Four different features of a 1H NMR spectrum provide information about the structure of a compound: 1. Number of signals. 2. Position of signals. 3. Intensity of signals. 4. Splitting of signals. Standard = tetramethylsilane: (CH 3 ) 4 Si These methyl groups are highly shielded.

8. Proton NMR Spectra - Methanol

9. Chemical Shift Values H Environment δH Environment δ (CH 3 ) 4 Si 0 (defined)R-COOCH ~3.5-4.5 Alkane -CH 3 ~0.9C=C-H ~4.5-6 -CH 2 - ~1.3 -CH- ~1.6Ar-H ~6.5-8 (C, N, O)=C-CH ~1.5-2.5R-CHO ~9-10 -C≡C-H ~2.5R-COOH ~10-12 (N, O)-CH ~2.5-4R-OH ; R-NH ~1-5

10. Chemical Shift Values

11. Proton NMR Spectra – chloromethyl methyl ether

12. Anisotropic Effects - Alkenes

13. Anisotropic Effects - Aromatic

14. Anisotropic Effects - Alkynes

15. Proton NMR Spectra - Toluene

16. Proton NMR Spectra – o-Xylene

17. Proton NMR Spectra – Acetic acid

18. Proton NMR Spectra – 4-hydroxy-4-methyl-2-pentanone

19. Proton NMR Spectra – Methyl acetoacetate

20. Spin-Spin Splitting Not all NMR signals are singlets. Some exist as doublets, triplets, or other multiplicities. The spin state of a proton within a three bond distance of another proton(s) feels the effect of the spin states of the other Hs. This effect of nonequivalent Hs on adjacent Cs is transmitted through the sigma bonds. The result of this interaction is that the NMR signal is split into (N + 1) peaks where N = the number of equivalent Hs. The distance between peaks of a multiplet are called J values (coupling constants) and are measured in Hz.

21. Proton NMR Spectra – Methanol CH 3 -OH

22. Proton NMR Spectra – 1,1,2-Tribromoethane

23. Proton NMR Spectra –  -chloroacetophenone

24. Proton NMR Spectra – 1-bromopropane

25. Proton NMR Spectra – 1,1,-dichloro-2,2-diethoxyethane

26. Proton NMR Spectra – Isopropyl Methyl ketone

27. Proton NMR Spectra – Ethylbenzene

28. END H 1 NMR

29. Proton NMR Spectra – bromocyclohexane