NMR Experimental Techniques

  1. H-1 NMR Data
    1. Experimental Description - 300 MHz proton NMR. 90 degree pulse.
    2. Spectral Interpretation
      1. Splitting Patterns, indicate number of protons on adjacent carbons.
      2. Integration, indicates relative number of protons.
      3. Chemical Shift (ppm), indicates chemical environment.

  2. Selective Homonuclear Decoupling
    1. Experimental Description - In this experiment the decoupler is set for a select frequency in the proton spectrum. This irradiates the nuclei at that frequency and selectivly decouples any nuclei coupled to the irradiated nuclei. As a result the splitting patterns will change.
    2. Spectral Interpretation - Select a frequency or chemical shift to decouple at. This will eliminate the irradiated nuclei (the one at the decoupler frequency). The splitting pattern for any nuclei coupled to the irradiated nuclei will change.

  3. C-13 NMR Data
    1. Experimental Description - 75 MHz Carbon NMR. Proton decoupled.
    2. Spectral Interpretation
      1. Chemical Shift (ppm), indicates chemical environment.
      2. These are decoupled spectra so no splitting information is present.
      3. Notice solvent peak (CDCl3) at ca 77 ppm.
      4. Quaternary carbon's frequently give small peaks.
      5. Acquisition conditions NOT optimized for integration

  4. Coupled Carbon Spectrum
    1. Experimental Description - In this experiment the proton decoupler is off. This produces a spectrum where carbons are coupled to adjacent protons. Because the spectral lines are split and there is no NOE, the spectrum has very low signal to noise. This experiment is not typically used for determining splitting patterns because the DEPT spectrum provides the same information, but with the polarization transfer the S/N is much higher.
    2. Spectral Interpretation. The chemical shift may be calculated from tables. The number of attached protons is determined by the splitting patterns (n-1). So that a carbon with no protons (quaternary) is observed as a singlet. A carbon with one proton is observed as a doublet. A carbon with two protons is observed as a triplet. And a carbon with three protons is observed as a quartet.

  5. Gated Decoupling
    1. Experimental Description - In this experiment the proton decoupler is pulsed to produce a spectrum where carbons are coupled, but the NOE (Nuclear Overhouser Effect) is allowed to build up by turning the decoupler on between pulses. This spectrum show splitting of carbon peaks, and the NOE enhances the S/N.
    2. Spectral Interpretation. The chemical shift may be calculated from tables. The number of attached protons is determined by the splitting patterns (n-1). So that a carbon with no protons (quaternary) is observed as a singlet. A carbon with one proton is observed as a doublet. A carbon with two protons is observed as a triplet. And a carbon with three protons is observed as a quartet.

  6. Inverse Gated Decoupling
    1. Experimental Description - In this experiment the proton decoupler is pulsed to produce a spectrum where carbons are decoupled, but the NOE (Nuclear Overhouser Effect) is not able to build up. This spectrum does not show splitting of carbon peaks, but it may be used to determine the NOE and it is useful for integration of carbon spectra.
    2. Spectral Interpretation. The chemical shift may be calculated from tables. Compare the signal intensity to the regular carbon spectrum to determine the NOE.

  7. Attached Proton Test
    1. Experimental Description - APT, Attached Proton Test.
    2. Spectral Interpretation - This pulse sequence produces a carbon spectrum where carbons with an even number of protons are in the opposite direction of carbons with an odd number of protons. The spectra here are phased so that carbons with an even number of protons (quaternary carbons and CH2 carbons) are up, while carbons with an odd number of protons (CH and CH3) are down.

  8. DEPT 45 NMR Data
    1. Experimental Description - DEPT 45, Distortionless Enhancement of Polarization Transfer using a 45 degree decoupler pulse.
    2. Spectral Interpretation - This pulse sequence produces a carbon spectrum containing only carbons with protons attached (quaternary carbons are not observed).

  9. DEPT 90 NMR Data
    1. Experimental Description - DEPT 90, Distortionless Enhancement of Polarization Transfer using a 90 degree decoupler pulse.
    2. Spectral Interpretation - This pulse sequence produces a carbon spectrum containing only Methyne (CH) carbons.

  10. DEPT 135 NMR Data
    1. Experimental Description - DEPT 135, Distortionless Enhancement of Polarization Transfer using a 135 degree decoupler pulse.
    2. Spectral Interpretation - This pulse sequence produces a carbon spectrum with methyl (CH3) and methyne (CH) carbons are up. Methene (CH2) carbons are down.

  11. T1 Inversion Recovery Experiment
    1. Experimental Description - In this experiment a 180 degree pulse is applied to the system. This causes the net magnitization vector to invert. The net magnitization vector recovers from this inversion at a rate that corresponds to T1. The recovery is measured by applying a 90 degree pulse after a delay period. This 90 degree pulse determines the amount of recovery that has occured. With a short delay, no recovery has occured and the peak is inverted (180 degrees out of phase). After complete recovery the peak has returned to it's initial intensity and phase. By measuring the intensity as a function of delay, the kinetics of the recovery are measured. A useful point is the null point where the system has recovered 50%. This is equivilent to the half life for T1.
    2. Spectral Interpretation - Each nuclei has a unique T1 recovery time. This recovery rate is useful for studying the spin system and it is useful for optimizing data acquisition. For accurate integration, you should wait 5 * T1 between experimental pulses. For other experiments to optimize the S/N you need to know the T1 rate to determine the optimum pulse angle.

  12. COSY NMR Data
    1. Experimental Description - 2D Corelation Spectroscopy Experiment.
    2. Spectral Interpretation - The COSY spectrum plots proton vs proton. The 1D spectrum is plotted along each axis. The 2D data consists of the matrix diagonal(not very useful), and the cross peaks. These peaks show which protons (from the diagonal) are coupled through bonds.

  13. HETCOR NMR Data
    1. Experimental Description - 2D Heteronuclear correlation spectroscopy.
    2. Spectral Interpretation - The HETCOR spectrum plots proton vs carbon. The 1D spectra are displayed along the appropriate axis. The 2D peaks show which protons are coupled to which carbons.

  14. NOESY NMR Data
    1. Experimental Description - 2D Correlation experiment that provides both Proton-Proton correlation (like the COSEY) and correlation from NOE to show protons that are coupled through space. The 1D proton spectrum is plotted along each axis. The 2D data consists of the matrix diagonal(not very useful), and the cross peaks. These peaks show which protons (from the diagonal) are coupled. This coupling is either through bonds, as in the COSY, or through space by NOE. These NOE peaks show which protons are close together in the three dimensional structure of the molecule.