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NMR N uclear M agnetic R esonance

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  1. NMRNuclear Magnetic Resonance HeteronuclearNMR: Index NMR-basics H-NMR NMR-Symmetry Heteronuclear-NMR

  2. Proton with Carbon-13 coupling

  3. Proton with Fluorine-19 coupling

  4. Fluorine-19:Fluoroacetone

  5. Phosphorus-31

  6. Phosphorus-31: Coupling with 1H

  7. Phosphorus-31 Coupling with 13C

  8. Phosphorus-31

  9. Silicon, Mercury, Carbon

  10. C-13 NMR

  11. C-13 NMR: Quantitative?? • In C-13, some carbons can have long relaxation time: If the relaxation delay is not long enough, the long relaxation carbons will not achieve full amplitude • NOEs varies for the various carbons • Number of data points used to record the data might not be sufficient • The efficiency of the pulse vary depending if a signal is in the center of the window or on the side.

  12. NOE and decoupler

  13. Carbon-13 Shift

  14. Alkanes d = -2.5 + SnA 1 2 3 4 5 CH3-CH2-CH-CH2-CH3 6 CH3 dC1 = -2.5 + 1a + 1b + 2g + 1d dC1 = -2.5 + 9.1 + 9.4 + 2(-2.5) + .3 = 11.3 dC2 = -2.5 + 2a + 2b + 1g + 2o(3o) (Secondary carbon bound to tertiary) dC2 = -2.5 + 18.2 + 18.8 + (-2.5) + (-2.5) = 29.5 dC3 = -2.5 + 3a + 2b + 2{3o(2o)} dC3 = -2.5 + 27.3 + 18.8 + (-7.4) = 36.2 dC6 = -2.5 + 1a + 2b + 2g + 1o(3o) = 19.3

  15. Alkanes dC1 = -2.5 + 1a + 1b + 2g + 1d = 11.3 dC2 = -2.5 + 2a + 2b + 1g + 2o(3o) = 29.5 dC3 = -2.5 + 3a + 2b + 2{3o(2o)} = 36.2 dC6 = -2.5 + 1a + 2b + 2g + 1o(3o) = 19.3 C2 C1 C3 C6 2 3 1 6

  16. Substituted Alkanes CH3-CH2-CH2-CH2-CH3 13.9 – 22.8 – 34.7 g b a CH3-CH2-CH-CH2-CH3 OH CH = 34.7 + 41 = 75.7 ppm CH2 = 22.8 + 8 = 30.0 ppm CH3 = 13.9 + (-5) = 8.9 ppm

  17. CH = 34.7 + 41 = 75.7 ppm g b a CH3-CH2-CH-CH2-CH3 CH2 = 22.8 + 8 = 30.0 ppm OH CH3 = 13.9 + (-5) = 8.9 ppm

  18. Shift Calculation: • Select a suitable model • Use proper substituent effects to predict the shifts of the various carbonsThis gives a crude estimate without taking into account the geometry • For cyclohexanes, substituents effects are compiled in terms of axial/equatorial orientation

  19. Cycloalkanes: Cyclohexane

  20. Alkenes: Additivity rules

  21. d- d+ CH2 CH OMe CH2 CH OMe 84.2 153.2 CH2 CH2 C C C d- d+ OEt CH C CH OEt C Unsaturated compounds: Electronic Effects Alkenes d- 129.3 d+ 157 Allenes 75-97 200-215 Alkynes 65-90 ppm 23.2 89.4

  22. Benzene Calculation

  23. Nitro-4-Aniline

  24. Example: Benzene Calculation => distinguish isomers

  25. H-NMR isomers

  26. Example: Benzene Calculation => distinguish isomers Experimental shifts 152.5, 136.6, 131.7, 126.3, 121.9, 116.3 Subst. C1 ortho meta para Me 9.2 0.7 -0.1 -3.0 CH(Me)2 20.2 -2.2 -0.3 -2.8 OH 26.9 -12.8 1.4 -7.4 C1 = 128 + 9.2 – 2.8 +1.4 = 135.8 C2 = 128 + .7 - 0.3 –7.4 = 121.0 C3 = 128 – 0.1 – 2.2 + 1.4 = 127.1 C4 = 128 – 3.0 + 20.2 – 12.8 = 132.4 C5 = 128 – 0.1 – 2.2 + 26.9 = 152.6 C6 = 128 + 0.7 – 0.3 – 12.8 = 115.6 C1 = 128 + 9.2 – 2.8 – 12.8 = 121.6 C2 = 128 + .7 - 0.3 + 1.4 = 129.8 C3 = 128 – 0.1 – 2.2 - 7.4 = 118.3 C4 = 128 – 3.0 + 20.2 + 1.4 = 146.6 C5 = 128 – 0.1 – 2.2 - 12.8 = 112.9 C6 = 128 + 0.7 – 0.3 + 26.9 = 155.3

  27. C1 = 128 + 9.2 – 2.8 +1.4 = 135.8 C2 = 128 + .7 - 0.3 –7.4 = 121.0 C3 = 128 – 0.1 – 2.2 + 1.4 = 127.1 C4 = 128 – 3.0 + 20.2 – 12.8 = 132.4 C5 = 128 – 0.1 – 2.2 + 26.9 = 152.6 C6 = 128 + 0.7 – 0.3 – 12.8 = 115.6

  28. C1 = 128 + 9.2 – 2.8 – 12.8 = 121.6 C2 = 128 + .7 - 0.3 + 1.4 = 129.8 C3 = 128 – 0.1 – 2.2 - 7.4 = 118.3 C4 = 128 – 3.0 + 20.2 + 1.4 = 146.6 C5 = 128 – 0.1 – 2.2 - 12.8 = 112.9 C6 = 128 + 0.7 – 0.3 + 26.9 = 155.3

  29. CarbonylsC=O Acid Ester

  30. CarbonylsC=OEsters, Acid chlorides, Anhydrides, Amides, Carbamates

  31. CarbonylsC=O : Ketones, Aldehydes

  32. Coupling between 1H and 13C1JCH One bond coupling is proportional to % s charactersp3 : ~125 Hzsp2: ~ 165 Hzsp : ~ 250 Hz Electronegative subst. Increase JCH-OR => J ~ 140 HzCH-Cl => J ~ 150 Hz

  33. Coupling between 1H and 13C sp3: 1JCH Increase of coupling values with the electronegativity of the substituant : CHZ Z : Li1JCH = 98 Hz Z : C1JCH = 125-129 Hz Z : NR1JCH = 131-134 Hz Z : S1JCH = 138 Hz Z : OR1JCH = 140 Hz Z : Cl1JCH = 150 Hz Z : (OR)21JCH = 162 Hz Z : Cl2 1JCH = 178 Hz 1JCH = 161 Hz 1JCH = 180 Hz 1JCH = 134 Hz 1JCH = 137 Hz 1JCH = 150 Hz

  34. Coupling between 1H and 13C sp2: 1JCH Increase of coupling values with the electronegativity of the substituant : =CHZ =C-H 1JCH = 157 Hz 1JCH = 238 Hz 1JCH = 172 Hz 1JCH = 250 Hz 1JCH = ~200 Hz 1JCH = 182 Hz 1JCH = 202 Hz

  35. Use of 1JCH Extremely useful for molecules where 1JCHlarger than usual Diagnostic for alkynes (250 Hz) , epoxides (180 Hz) , hemiacetal (162 Hz) and cyclopropane (161 Hz)

  36. Coupling between 13C and 13C : 1JCC Measurable only on enriched compound Useful for setting up pulse sequences like INADEQUATE sp3 R-CH2-CH31JCC = 35 Hz 1JCC = 48 Hz sp2 1JCC = 44 Hz 1JCC = 56 Hz 1JCC = 54 Hz 1JCC = 74 Hz 1JCC = 74 Hz 1JCC = 123 Hz

  37. Coupling between 1H and 13C2JCH Usually small and difficult to predict Typical values: -8 to +4 Hz

  38. Coupling between 1H and 13C3JCH Depend on dihedral angle between coupled nuclei: Karplus curve 0 angle : 3JC-H ~ 3-7 Hz 90 angle : 3JC-H ~ 0 Hz 180 angle: 3JC-H ~ 7-12 Hz This behavior (Jcis < Jtrans) is useful specially in sp2 carbons to help distinguishing isomers

  39. 3J : example of usage

  40. C-13 Coupling with other nuclei than H 1JCD = 20 Hz 1JCF = -160 Hz 1JCN = 6-8 Hz 1JP-H = >600 Hz

  41. 15N – NMRAmine

  42. 15N – NMRAmide

  43. 15N – NMRAromatic

  44. 29Si – NMR

  45. 19F – NMR Index NMR-basics H-NMR NMR-Symmetry Heteronuclear-NMR Dynamic-NMR