Nuclear Magnetic Resonance (NMR) Spectroscopy

1. Nuclear Magnetic Resonance (NMR) Spectroscopy Dr. Vincent J. Storhaug

2. Deuterated Solvent Signals in 13C NMR Spectra Why do you see this as a triplet at 77 ppm? 1JCD= 45 Hz n = number of nuclei I = spin quantum number What do you expect the multiplicity to be for Acetone-d6 (C3D6O)?

3. 90º Pulse Calibration: Off Resonance Resonance Line Transmitter Frequency

4. Advantages to Using Higher Applied Fields 60 MHz – propyl bromide 300 MHz – propyl bromide

5. Advanced NMR Experiments Advanced NMR Experiments Two Dimensional Homonuclear 1H-1H Correlation Heteronuclear 13C-1H, 15N-1H, 13C-15N Correlation One Dimensional 1-Channel 2-Channel Solvent Suppression HOMODEC NOEDIF DEPT INEPT

6. The Problem: Solvent Signal or an Undesired HOD Signal is Flooding the Sample

7. A Situation Where RECEIVER GAIN Doesn’t Work to Your Advantage

8. The Problem: Solvent Signal or an Undesired HOD Signal is Flooding the Sample

9. A Situation Where RECEIVER GAIN Doesn’t Work to Your Advantage

10. Solvent Suppression Three commonly used techniques: Using the Decoupler to provide Presaturation (Good) Using a Series of Pulses to provide Presaturation (Better) Using Pulse Sequences involving the Gradients (Best) Set up the experiment the same as a homodec experiment – homonuclear decoupling. *Changes the experiment from a one-pulse experiment to a two-pulse experiment.

11. One-Channel Two-Pulse Sequence n y n d1 delay 1 at acquisition time pw1 d2 delay 2 pw2 time 0 s (more if needed) 2 s

14. Homonuclear Decoupling Experiment n n y d1 delay 1 at acquisition time pw1 d2 delay 2 pw2 time 5*T1 0 s

15. Homonuclear Decoupling Experiment 7 5 3 1

16. Homonuclear Decoupling Experiment 7 5 3 1

17. Homonuclear Decoupling Experiment 7 5 3 1

18. Homonuclear Decoupling Experiment 7 5 3 1

19. Homonuclear Decoupling Experiment 7 5 3 1

20. Homonuclear Decoupling Experiment 7 5 3 1

21. HOMODEC Experiment – Ethyl Crotonate Expanded 1H spectrum for ethyl crotonate. (a) Control spectrum. (b) Spectrum with 4-Me group irradiated. (c) Spectrum with H-2 irradiated.

22. NOEDIF Experiment The Nuclear Overhauser Effect is a net change of the signal intensity of one spin due to the relaxation of a saturated spin that is dipole-dipole coupled to the first spin. An NOE may be positive OR negative (the latter is more common for large molecules) NOE’s develop through space rather than through bonds (i.e. – through dipole-dipole interactions and not through J coupling) T1 is the key! Fluctuating fields are good, tumbling and molecules are bad.

25. 2D NMR Acronymns NOESY NOE Spectroscopy ROESY Rotating-Frame NOE Spectroscopy COSY Correlation Spectroscopy TOCSY Total Correlation Spectroscopy HETCOR Heteronuclear Correlation Long Range HETCOR Long Range Heteronuclear Correlation COLOC Correlation through Long-Range Coupling HSQC Heteronuclear Single Quantum Correlation HMBC Heteronuclear Multiple-Bond Correlation EXSY Exchange Spectroscopy APT Attached Proton Test Solvent Suppression Methods WATERGATE Water Suppression Through Gradient Tailored Excitation SECSY Spin Echo Correlated Spectroscopy DANTE Delay Alternating with Nutation for Tailored Excitation CHESS Chemical Shift Selective Imaging Sequence INADEQUATE Incredible Natural Abundance Double Quantum Transfer Experiment DUMBO Decoupling Using Mind Boggling Optimization GROPE Generalized Compensation for Resonance Offset and Pulse Length Errors DOUBTFUL Double Quantum Transitions for Finding Unresolved Lines

26. pw180 pw180 13C NMR - DEPT(Distortionless Enhancement of Polarization Transfer) mult*pw90 pw90 pw90 Dec pw90 pw90 pw90 pw90 mult is an arrayed parameter (0.5, 1, 1, 1.5) that leads to a value for the θ pulse of mult*pp: mult=0.5 (θ = 45°) gives approximately equal excitation of all protonated carbons mult=1.0 (θ = 90°) excites CH’s only (or mainly) mult=1.5 (θ = 135°) gives CH’s, CH3’s up, CH2’s down. dm (decoupler modulation) is set to 'nny'.

27. 13C NMR - DEPT(Distortionless Enhancement of Polarization Transfer) In a DEPT135 experiment: -CH3 and CH peaks appear as normal -CH2- peaks appear inverted Quaternary C are not usually seen This way the number of H attached to C can usually be deduced. Standard 13C NMR Spectrum of ethylbenzene

28. 13C NMR - DEPT(Distortionless Enhancement of Polarization Transfer) In a DEPT135 experiment: -CH3 and CH peaks appear as normal -CH2- peaks appear inverted Quaternary C are not usually seen This way the number of H attached to C can usually be deduced. Standard 13C NMR Spectrum of ethylbenzene

30. DEPT 135

31. DEPT 90 DEPT 135