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: 67.28 vs. 1 H 267.53-1/2 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 (10-100 sec vs. 0.1-1 sec for 1 H) 13 C- 1 H coupling complictes spectrum; decreses pek intensity
see lso Pvi Tble 6.1; Appendices 7 & 8 Chemicl Shift
Chemicl Shift Fctors the Influence Chemicl Shift 1. hybridiztion 2. electronegtivity of element bonded to crbon 3. nisotropy * * * δ 22.6 δ 139.0 δ 38.2 H * * δ 62.3 δ 202.8
Differences Between 1 H nd 13 C NMR 1. rnge of 13 C chemicl shifts is very lrge compred to 1 H 2. 13 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 1.32 1.32 3.62 22.8 25.8 61.9 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 0.90 1.32 1.56 14.2 32.0 32.8 See Pvi, Appendix 8 for clcultion of 13 C chemicl shifts 4. Homonucler ( 13 C / 13 C) splitting is not observed
NMR Spectr of n-butylbenzene
Heteronucler Spin-Spin Splitting ( 1 H- 13 C) 3 J = 0-3 Hz CH 2 CH 2 CH 3
H H Heteronucler Spin-Spin Splitting H H H cholesterol 1 H coupled spectrum 1 H decoupled spectrum
Proton Decoupled 13 C NMR
Proton Decoupled 13 C NMR 1 H coupled spectrum CH 3 CH 3 1 H brodbnd decoupled spectrum 1 H off resonnce decoupled spectrum
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 = 1 1 13 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
13 C Pulse Sequence FID:
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 3 9.3 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
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
Integrtion A 2 peks B C 1 D 2 3 4
Distortionless Enhncement by Polriztion Trnsfer (DEPT) DEPT-45 DEPT-90 DEPT-135 C 0 0 0 CH + + + CH 2 + 0 - CH 3 + 0 +
Distortionless Enhncement by Polriztion Trnsfer (DEPT) C CH CH 2 CH 3 DEPT-45 0 + + + DEPT-90 0 + 0 0 DEPT-135 0 + - + 4 7 CH 3 5 6 DEPT-135 3 2 1 H H 3 C 8 CH 3 9 9 menthol DEPT-90 DEPT-45 13 C NMR 1 2 4 6 5 7 8 3 9 9
H 13C NH H Nucler Mgnetic Resonnce DEPT-135 CH3 CH32C H CH3 H H
Alknes 2-methylpentne R CH 3 R 2 CH 2 R 3 R 4 chemicl shifts CH C 8-30 ppm 15-55 ppm 20-60 ppm 30-40 ppm CH 3 CH 3 CH-CH 2 -CH 2 -CH 3 b c d e c b d e
Alkenes C C chemicl shifts 110-150 ppm cis-2-hexene H H b C C c 130.7 c 123.9 b 29.1 d e f H 3 C CH 2 CH 2 CH 3 d e f
chemicl shifts Alkenes 1-hexene C C 110-150 ppm f e d c b CH 3 -CH 2 -CH 2 -CH 2 -CH CH 2 114.2 139.2 b
Alkenes C C chemicl shifts 110-150 ppm dihydropyrn b 144.3 100.7 b
Alkenes C C chemicl shifts 110-150 ppm 4-methyl-2-penten-1-one 154.8 b 124.3 H 3 C H 3 C b CH 3
Aromtics chemicl shifts C 110-175 ppm nitrobenzene c b N 2 c b d d
Aromtics chemicl shifts C 110-175 ppm p-cymene CH 3
Aromtics chemicl shifts C 110-175 ppm dichlorobenzenes Cl Cl Cl Cl Cl Cl
chemicl shifts Alkynes 2-heptyne C C 65-90 ppm CH 3 CH 2 CH 2 CH 2 b C C CH 3 79.4 75.3 b
Alkyl Hlides C C chemicl shifts I Br -5-40 ppm 25-65 ppm 1-chloropentne C Cl 35-80 ppm CH 3 CH 2 -CH 2 -CH 2 -CH 2 -Cl 45.1
Alcohols, Ethers & Amines 2-hexnol C-R C-NR 2 chemicl shifts 50-80 ppm 40-60 ppm H CH 3 CH 2 CH 2 CH 2 CHCH 3 68.0
Alcohols, Ethers & Amines 1,3-dioxne C-R C-NR 2 chemicl shifts 50-80 ppm 40-60 ppm c b b c
Alcohols, Ethers & Amines N-methylisobutylmine C-R C-NR 2 chemicl shifts 50-80 ppm 40-60 ppm b d N H c d b c
Crbonyl Compounds ldehydes & ketones 185-220 ppm crboxylic cids, esters, mides, etc. 155-185 ppm nitriles 110-140 ppm
Aldehydes & Ketones 2-hexnone R R C H C R' chemicl shifts 185-200 ppm 205-220 ppm CH 3 C CH 2 -CH 2 -CH 2 -CH 3 209.0
chemicl shifts 13 R C H 175-185 ppm Crboxylic Acid Derivtives methcrylic cid R R C C R' NR' 2 165-175 ppm 165-175 ppm H C C CH 2 CH 3 173.5
chemicl shifts 13 R C H 175-185 ppm Crboxylic Acid Derivtives heptyl cette R R C C R' NR' 2 165-175 ppm 165-175 ppm CH 3 C -CH 2 CH 2 -CH 2 -CH 2 -CH 2 -CH 2 -CH 3 b 64.6 b 171.0
chemicl shifts 13 R C H 175-185 ppm Amides N-methyl-6-hexnelctm R R C C R' NR' 2 165-175 ppm 165-175 ppm d 36.9 b b N CH 3 c 51.3 c 175.7 d 35.7
chemicl shifts Nitriles hexnenitrile R C N 110-140 ppm CH 3 CH 2 CH 2 CH 2 C N 119.9
Heteronucler Coupling to Deuterium multiplicity D C b J b = 45 Hz multiplicity = 2nI + 1 where: n = # of nuclei I = spin reltive intensity
Solvent Peks CDCl 3 D 3 C(S=)CD 3
Heteronucler Coupling to 19 F fluorotribromomethne F C J F = ~350 Hz F C C b J Fb = ~50 Hz 1 J = 370 Hz
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
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)
P C P C C b Heteronucler Coupling to 31 P J P, J Pb vrible tetrmethylphosphonium chloride (proton decoupled) 1 J = 56 Hz
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
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
1 H Nucler Mgnetic Resonnce Reporting 13 C NMR Dt (1H decoupled) ppm 119.90 30.87 25.21 21.96 17.11 13.78 Int 261 970 1000 920 814 950 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, 22.0. 17.1, 13.8.
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, 22.0. 17.1, 13.8. frequency (1/4 1 H frequency) solvent *if two peks round to sme vlue, cn dd second deciml plce (e.g. 69.87, 69.89);
Chemicl Shift