C Nuclear Magnetic Resonance

Transcription

1 Inherent Difficulties Low bundnce of 13 C (1.1% vs, 99.9% for 1 H) Lower gyromgnetic rtio (1/4 tht of 1 H) - 13 C: vs. 1 H /2 1,000,000 nuclei t 60 MHz E ΔE +1/2 1,000,009 nuclei t 60 MHz mgnetic field (B 0 ) Slow T 1 relxtion times ( sec vs sec for 1 H) 13 C- 1 H coupling complictes spectrum; decreses pek intensity

2 see lso Pvi Tble 6.1; Appendices 7 & 8 Chemicl Shift

3 Chemicl Shift Fctors the Influence Chemicl Shift 1. hybridiztion 2. electronegtivity of element bonded to crbon 3. nisotropy * * * δ 22.6 δ δ 38.2 H * * δ 62.3 δ 202.8

4 Differences Between 1 H nd 13 C NMR 1. rnge of 13 C chemicl shifts is very lrge compred to 1 H C chemicl shifts re more sensitive to smll chnges in chemicl environment 3. Influence of electronegtive toms on chemicl shift greter in 13 C NMR thn 1 H NMR 1 H shifts 13 C shifts CH 3 CH 2 CH 2 CH 2 CH 2 CH 2 H CH 3 CH 2 CH 2 CH 2 CH 2 CH 2 H See Pvi, Appendix 8 for clcultion of 13 C chemicl shifts 4. Homonucler ( 13 C / 13 C) splitting is not observed

5 NMR Spectr of n-butylbenzene

6 Heteronucler Spin-Spin Splitting ( 1 H- 13 C) 3 J = 0-3 Hz CH 2 CH 2 CH 3

7 H H Heteronucler Spin-Spin Splitting H H H cholesterol 1 H coupled spectrum 1 H decoupled spectrum

8 Proton Decoupled 13 C NMR

9 Proton Decoupled 13 C NMR 1 H coupled spectrum CH 3 CH 3 1 H brodbnd decoupled spectrum 1 H off resonnce decoupled spectrum

10 Nucler verhuser Effect & Cross Polriztion of Spin 1 H decoupler 300 MHz B 0 Boltzmn distribution N upper N lower = 1,000,000 1,000,048 = 1,000,000 1,000,000 = C cross polriztion B 0 Boltzmn distribution N upper N lower = 1,000,000 1,000,048 = 1,000,000 1,000,096 Signl Enhncement: CH 3 > CH 2 > CH >> C

11 13 C Pulse Sequence FID:

12 Relxtion Times (T 1 ) in generl 68 s 9.8 s T 1 : C > CH > CH 2 > CH 3 CH 3 CH 3 CH 3 C CH 2 CH CH 3 CH s 13 s 23 s tumbling H H T 1 = 37 s T 1 = 20 s H H H T 1 = 1-2 s for CH, CH 2, CH 3 T 1 = 4-6 s for quternry C

13 Moleculr Symmetry How Mny Lines? CH 3 H 3 C CH 3 C-CH 2 -CH 3 CH 3 H 3 C CH 3 H H 3 C CH 3 A B C D

14 Integrtion A 2 peks B C 1 D 2 3 4

15 Distortionless Enhncement by Polriztion Trnsfer (DEPT) DEPT-45 DEPT-90 DEPT-135 C CH CH CH

16 Distortionless Enhncement by Polriztion Trnsfer (DEPT) C CH CH 2 CH 3 DEPT DEPT DEPT CH DEPT H H 3 C 8 CH menthol DEPT-90 DEPT C NMR

17 H 13C NH H Nucler Mgnetic Resonnce DEPT-135 CH3 CH32C H CH3 H H

18 Alknes 2-methylpentne R CH 3 R 2 CH 2 R 3 R 4 chemicl shifts CH C 8-30 ppm ppm ppm ppm CH 3 CH 3 CH-CH 2 -CH 2 -CH 3 b c d e c b d e

19 Alkenes C C chemicl shifts ppm cis-2-hexene H H b C C c c b 29.1 d e f H 3 C CH 2 CH 2 CH 3 d e f

20 chemicl shifts Alkenes 1-hexene C C ppm f e d c b CH 3 -CH 2 -CH 2 -CH 2 -CH CH b

21 Alkenes C C chemicl shifts ppm dihydropyrn b b

22 Alkenes C C chemicl shifts ppm 4-methyl-2-penten-1-one b H 3 C H 3 C b CH 3

23 Aromtics chemicl shifts C ppm nitrobenzene c b N 2 c b d d

24 Aromtics chemicl shifts C ppm p-cymene CH 3

25 Aromtics chemicl shifts C ppm dichlorobenzenes Cl Cl Cl Cl Cl Cl

26 chemicl shifts Alkynes 2-heptyne C C ppm CH 3 CH 2 CH 2 CH 2 b C C CH b

27 Alkyl Hlides C C chemicl shifts I Br ppm ppm 1-chloropentne C Cl ppm CH 3 CH 2 -CH 2 -CH 2 -CH 2 -Cl 45.1

28 Alcohols, Ethers & Amines 2-hexnol C-R C-NR 2 chemicl shifts ppm ppm H CH 3 CH 2 CH 2 CH 2 CHCH

29 Alcohols, Ethers & Amines 1,3-dioxne C-R C-NR 2 chemicl shifts ppm ppm c b b c

30 Alcohols, Ethers & Amines N-methylisobutylmine C-R C-NR 2 chemicl shifts ppm ppm b d N H c d b c

31 Crbonyl Compounds ldehydes & ketones ppm crboxylic cids, esters, mides, etc ppm nitriles ppm

32 Aldehydes & Ketones 2-hexnone R R C H C R' chemicl shifts ppm ppm CH 3 C CH 2 -CH 2 -CH 2 -CH

33 chemicl shifts 13 R C H ppm Crboxylic Acid Derivtives methcrylic cid R R C C R' NR' ppm ppm H C C CH 2 CH

34 chemicl shifts 13 R C H ppm Crboxylic Acid Derivtives heptyl cette R R C C R' NR' ppm ppm CH 3 C -CH 2 CH 2 -CH 2 -CH 2 -CH 2 -CH 2 -CH 3 b 64.6 b 171.0

35 chemicl shifts 13 R C H ppm Amides N-methyl-6-hexnelctm R R C C R' NR' ppm ppm d 36.9 b b N CH 3 c 51.3 c d 35.7

36 chemicl shifts Nitriles hexnenitrile R C N ppm CH 3 CH 2 CH 2 CH 2 C N 119.9

37 Heteronucler Coupling to Deuterium multiplicity D C b J b = 45 Hz multiplicity = 2nI + 1 where: n = # of nuclei I = spin reltive intensity

38 Solvent Peks CDCl 3 D 3 C(S=)CD 3

39 Heteronucler Coupling to 19 F fluorotribromomethne F C J F = ~350 Hz F C C b J Fb = ~50 Hz 1 J = 370 Hz

40 Heteronucler Coupling to 19 F 2,2,2-trifluoroethnol (proton decoupled) F C J F = ~350 Hz F C C b J Fb = ~50 Hz 2 J = 35 Hz 1 J = 278 Hz

41 Heteronucler Coupling to 19 F commonly observed systems F C J F = ~350 Hz F C C b J Fb = ~50 Hz F 3 C C R F 3 C S R trifluorocettes trifluoromethnesulfontes (trifltes)

42 P C P C C b Heteronucler Coupling to 31 P J P, J Pb vrible tetrmethylphosphonium chloride (proton decoupled) 1 J = 56 Hz

43 P C P C C b Heteronucler Coupling to 31 P J P, J Pb vrible dimethyl methylphosphonte (proton decoupled) 2 J = 6 Hz 1 J = 144 Hz

44 1 H Nucler Mgnetic Resonnce How to Interpret 13 C NMR Spectrum 1. Get n verview identify ny reference solvents in proton decoupled spectrum 2. Symmetry: count the number of crbons (remember 13 C is not integrted) verify crbon count bsed on the moleculr formul is there ny symmetry? - rrely see overlp of peks in bsence of symmetry - ok to see fewer crbons (if resonble); not oky to hve more! 3. Chemicl Shift: determine the chemicl shift of ech resonnce in the spectrum - wht functionl groups my be present - consider the presence of heterotoms 4. If Needed Collect DEPT Dt determine how mny Hs re on ech crbon 5. Put it ll Together: often helpful to consider 1 H NMR dt simultneously

45 1 H Nucler Mgnetic Resonnce Reporting 13 C NMR Dt (1H decoupled) ppm Int CH 3 CH 2 CH 2 CH 2 CH 2 C N 13 C NMR (25 MHz, CDCl 3 ) δ 119.9, 30.9, 25.2, , 13.8.

46 1 H Nucler Mgnetic Resonnce Reporting 13 C NMR Dt (1H decoupled) list chemicl shift of ech pek to 1 deciml plce* 13 C NMR (25 MHz, CDCl 3 ) δ 119.9, 30.9, 25.2, , frequency (1/4 1 H frequency) solvent *if two peks round to sme vlue, cn dd second deciml plce (e.g , 69.89);

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48 Chemicl Shift