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13.7 Spin-Spin Splitting in NMR Spectroscopy

13.7 Spin-Spin Splitting in NMR Spectroscopy. not all peaks are singlets signals can be split by coupling of nuclear spins. Chapter 13; Spectroscopy. Analysis of 1 H-NMR Spectrum Spin-spin Splitting (n+1) rule J Values Complex splitting Analysis of 13 -C NMR Spectrum.

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13.7 Spin-Spin Splitting in NMR Spectroscopy

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  1. 13.7Spin-Spin SplittinginNMR Spectroscopy not all peaks are singlets signals can be split by coupling of nuclear spins

  2. Chapter 13; Spectroscopy • Analysis of 1H-NMR Spectrum • Spin-spin Splitting (n+1) rule • J Values • Complex splitting • Analysis of 13-C NMR Spectrum

  3. 1H-NMR of 1,1,2-tribromoethane

  4. H H C C Spin-Spin Splitting • Coupling (interaction) of nonequivalent, vicinal protons • (n+1) Rule; If a 1H nucleus has n nonequivalent, vicinal neighbors, its NMR signal will split into (n+1) peaks protons separated bythree bonds(vicinal relationship)

  5. 10.0 9.0 8.0 7.0 6.0 5.0 4.0 3.0 2.0 1.0 0 Cl2CHCH3 Figure 13.12 (page 536) 4 lines; quartet 2 lines; doublet coupled protons are vicinal (three-bond coupling) CH splits CH3 into a doublet CH3 splits CH into a quartet CH3 CH Chemical shift (, ppm)

  6. H Cl H H C C H Cl this line correspondsto molecules in which the nuclear spin of the proton at C-1 reinforcesthe applied field this line correspondsto molecules in which the nuclear spin of the proton at C-1 opposesthe applied field Why do the methyl protons of1,1-dichloroethane appear as a doublet? "true" chemicalshift of methylprotons (no coupling)

  7. H Cl H H C C H Cl Why does the methine proton of1,1-dichloroethane appear as a quartet? There are eight combinations of nuclear spins for the three methyl protons. These 8 combinations split the signal into a 1:3:3:1 quartet.

  8. Number of equivalent Appearance Intensities of linesprotons to which H of multiplet in multipletis coupled 1 Doublet 1:1 2 Triplet 1:2:1 3 Quartet 1:3:3:1 4 Pentet 1:4:6:4:1 5 Sextet 1:5:10:10:5:1 6 Septet 1:6:15:20:15:6:1 Splitting Patterns of Common Multiplets

  9. 10.0 9.0 8.0 7.0 6.0 5.0 4.0 3.0 2.0 1.0 0 BrCH2CH3 The Ethyl Group 4 lines; quartet 3 lines; triplet CH3 CH2 Chemical shift (, ppm)

  10. 10.0 9.0 8.0 7.0 6.0 5.0 4.0 3.0 2.0 1.0 0 BrCH(CH3)2 IsoPropyl Group 2 lines; doublet 7 lines; septet CH3 CH Chemical shift (, ppm)

  11. 1H-NMR Spectrum

  12. 1H-NMR Spectrum

  13. 1H-NMR Spectrum

  14. 1H-NMR Spectrum

  15. Complex Splitting PatternsMultiplet of Multiplets Coupling Constant; J; • Describes the distance in separation of peaks in a multiplet. Jab is always the same

  16. Spin-spin splitting pattern for..

  17. Spin-spin splitting pattern for..

  18. H H H O2N 16 Hz m-Nitrostyrene; The Ha signal appears as a doublet of doublets. a Jac = 16 Hz c b Jac = 12 Hz 12 Hz 12 Hz

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