ORGANIC NMR INTERPRETATION

1. p. 101 ORGANIC NMR INTERPRETATION

2. p. 101 ALKANES AND ALKYL HALIDES CH3—CH2—CH2—C d 0.9 1.3 CH3—F 4.3 CH3—O- 3.5 CH3—Cl 3.0 CH3—Br 2.7 CH3—I 2.2 Dd ~ 2 ppm downfield CH3—CH2- CH3—X

3. p. 102 Inductive effects CH3—CH2—CH2—C d0.91.3 CH3—CH2—CH2Cl d 1.01.83.5 Effect falls off with distance and is ~ 0 two C away CH3—CH2—CH2Br d 1.01.83.4 CH3—CH2—CH2I d 1.01.83.2 Dd 0 ½ 2

4. p. 102 CH3—CH2—CH2Cl 1.01.83.5 CH3—CH2—CH2Br 1.01.83.4 CH3—CH2—CH2I 1.01.83.2 Dd 0 ½ 2 CH3—CH2— d0.91.3

5. p. 103 CH3—CH2—CH2X CH3—CH2— d0.91.3 Dd 0 ½ 2 Each extra X adds ~ 2 ppm CH3—X CH2X2 CHX3 d 3 5 7 Ballpark ONLY!! Inductive effects are more or less additive

6. p. 103 CH3—CH2—I d 1.8 3.2 I—CH2—CH2—I d 3.6 Additional X next door has added about ½ ppm

7. p. 103 In general, the more substituted, the more downfield CH3—I CH3—CH2—I (CH3)2CH—I d2.23.24.2 but additional alkyl groups are not as strong as –X CH3CH2Br = 3.4 (CH3)2CHBr =4.3 CH3CHBr2 = 5.5 split by 1 = 1+1 split by 6 = 6+1 I—CH(CH3)2 6H 1H

8. p. 104 More complex splittings I—CH2—CH2—CH2—CH3 t ? ? t What about when neighbors are chemically different? If J’s are same, then can use splitting (# of lines) = total # of H neighbors + 1 Characteristic chain splitting in alkane chains J=7 J=7 J=0

9. p. 104 More complex splittings I—CH2—CH2—CH2—CH3 t 5 6 t 2+2+12+3+1

10. p. 105 ANISOTROPIC EFFECTS F Spherical atoms have same effect in all directions are above and below the plane of molecule p-electrons so electron density is different above or below molecule than in plane

11. p. 105 so alkenes and aromatics (and other p-bonds) are not isotropic – they have effects that are different in different directions – we call them ANISOTROPIC p = Bp-electrons = Blocal so H feels B0 + Blocal so appear at low field

12. aromatics & alkenes appear at LOW FIELD - is shielded (to lower ppm) - + + is deshielded (to higher ppm) - p. 105

13. p. 106 aromatic hydrogens ~ d 7 7.22.3 7.02.3 6.82.3 X=C—CH3 methyl on an aromatic ring, double bond or carbonyl ~2.3

14. p. 107 Ph—CH2—CH2—(CH2)4—CH2—CH3 7.1-7.3 2.61.61.3 1.30.9 Ph—CH2—CH2—(CH2)6—CH2—CH3

15. p. 107 Clearing up some terminology: Downfield Deshielded Low field Greater d Upfield Shielded High field Smaller d

16. p. 108 EWG Electron Withdrawing Groups (EWG) deshield the ortho & para H’s, o > p Benzene = 7.3 7.8 7.3 7.6 -CHO -COR -COOH -COOR -CN -NO2 -SO2 resonance effects +ve charge deshields: less electron density at the C and H

17. 2:1:2 CHO d 10 EWG deshield 7.8 7.3 7.6 p. 108

18. p. 109 D Electron Donating groups (D:) SHIELD the ortho and para protons o > p 6.8 7.2 7.0 Donating groups are X: (atoms with lone pairs but not halogens) e.g. -OH -OR -NH2 -NHR -NR2 -SR -R resonance effect dominates inductive effect negative charge shields: more electron density at C and H

19. p. 109 OCH3 6.8-6.9 CH3 on O + Ar ring ~ 3.8 7.2 6.9-7.0

20. p. 110 HALOGENS Not easy to predict: Lone pairs shield by resonance but deshield because of high electronegativity

21. Part of Table on manual page 110 Increments add to d 7.27 to predict shifts, e.g. Proton ortho to –CHO will be 7.27 + 0.58 = 7.85

22. p. 110

23. p. 110 Look carefully at peaks, they are doublets 3J ~ 8 Hz What about to other protons?

24. p. 111 H 3JORTHOH-H = ~8Hz 4JMETAH-H = ~2Hz H 5JPARAH-H= ~0 Hz H H

25. p. 111 At high fields, can use trees to get patterns, IF chemical shifts are far apart (called 1st order spectrum if Dd >> J) H= d (H) of d (H) H 8Hz 2Hz H= t (HH) of d (H) H 8,8 2 H H= t (HH) of d (H) H H= d (H) of d (H)

26. p. 112 O=C-H ALDEHYDES - is shielded (to lower ppm) + is deshielded (to higher ppm) d ~ 10 AND coupling constant to neighbors is small

27. Karplus showed relationship of J and a a p. 112

28. p. 113 60MHz 60Hz Spectrum looks different on different instruments J in Hertz is always independent of field 30Hz

29. p. 114 ALKENE COUPLING CONSTANTS 16Hz 8Hz 2Hz

30. p. 114 mono-substituted alkene R--CH=CH2 Always 12 lines: d(JL)d(JM) d(JL)d(JS) d(JM)d(JS)

31. p. 115 Jcis Jtrans

32. p. 116

33. p. 117 Chemical shifts – much like aromatics ‘normal’ = 5.25 ppm Geminal (same C) always deshield by ~ 1ppm b to the substituent feels resonance effect

34. Manual, table page 117 Always deshield geminal Shield b Deshield b

35. p. 118 4J = ~1Hz Cis Me 3J = ~7Hz Gem H Trans Ph 4J = ~1Hz d cis to Me = 5.25 + 0 - 0.22 – 0.07 = 4.96 d cis to Ph = 5.25 + 0 + 0.36 – 0.28 = 5.33 See yellow pages A5 Cis Ph H Trans Me H

36. ALCOHOLS, AMINES, AMIDES AND ACIDS– exchangeable H’s Ar-CONHR and Ar-CONH2 More acidic means more d+ on H NMR time scale is ~ 10-2 – 10-3 sec fastest NMR can measure! p. 119

37. p. 119 Since acidic H exchange between molecules occurs faster than the NMR time scale they DO NOT show coupling to any neighbours and are typically broadened

38. p. 119 To prove which is –OH peak, add D2O and shake ROH + D2O => ROD + HOD d ~ 5.2

39. p. 120 Shape of peak depends upon temperature (rate of exchange is affected by temperature) exchange stopped Coupling visible slow exchange fast exchange HO—CH3

40. p. 121 Only a triplet Amines: RNH2d 1-5; ArNH2d 5-10

41. p. 121 Amides: d 5-10 Why 2?

42. p. 121 Acids: d 10-16 d = 9.85 + offset (2.0) = 11.85

43. You can now start Assignment 5