General Information and experimental capabilities:

The NMR Laboratory contains 3 NMR spectrometers:

  • Varian INOVA 500 (VI-500)
  • Varian INOVA 400 (VI-400)
  • Varian Mercury VX 200 (VMVx-200)

This document describes operation of the Varian NMR spectrometers.

  • The standard probe for the VI-500 is a triple-resonance indirect detection PFG probe that is set up to observe H1 directly and C13or N15 nuclei indirectly and is equipped with pulsed field gradients (PFG).
  • The standard probe for the VI-400 is a 4-nucleus probe equipped to observe H1, C13, F 19, and P 31.
  • The standard probe for the VMVx-200 is a broadband probe that is set up to observe H1 and C13 nuclei.
  • The VI-500 and VI-400 spectrometers are equipped with additional probes that can be tuned to most other nuclei. Contact Ata for information on scheduling times to do other nuclei.
  • The VI-400 and VI-500 are quipped for temperature control. Separate training is required for use of the variable temperature equipment.
    • The VT range of the standard PFG probe in the VI-500 is -20C to +60C.
    • The VT range of the standard probe in the VI-400 is -100C to +100C.
    • Other probes are available on these instruments that can go from -100C to +100C.
  • A Sun workstation is located in the NMR lab for off-line processing of data. Use this workstation for processing and plotting of data. Our goal is to maximize the amount of time the spectrometers are busy collection data.
  • To run non-routine experiments (VT or non-standard nuclei), schedule time with Ata one week in advance.

References:

This document is designed to briefly describe how to operate the Varian NMR spectrometers. For more information on operation of the spectrometers see the on-line version of the Varian manuals:
  • Getting Started: more details on general operating instructions
  • User Guide: Liquids NMR description of experiments and relevant parameters
  • Command and Parameter Reference: alphabetical list of commands and parameters with a thorough description of what they do (also available on-line on the Sun Computers).
For general information on NMR spectroscopy see:
  • Modern NMR Techniques for Chemistry Research by Andrew E Derome Good description of NMR fundamentals and tips on how to get good NMR spectra- everything from sample preparation to data acquisition to data processing and analysis
  • High-Resolution NMR Techniques in Organic Chemistry by Timothy D.W. Claridge Update of Derome, including current techniques such as gradients.
  • Basic One- and Two- Dimensional NMR Spectroscopy by Horst Friebolin Good information on interpretation of NMR spectra.
  • Structure Determination of Organic Compounds by Pretsch, Buhlmann, and Affolter Tables of spectral data

Rules:

  • All users must be trained by the NMR lab personnel- NO UNAUTHORIZED USERS.
  • Each authorized user is given a user name and computer account for scheduling time on the instruments and for using the instruments. Use a secure password and do NOT let anyone else use your account. This is grounds for suspension.
  • No food or beverages in the lab.
  • No chemistry in the NMR lab. This includes adding solvent to your NMR tubes. We are not quipped with fume hoods and do not want to deal with spilled chemicals or solvents.
  • Do NOT leave NMR tubes in the NMR lab.
  • No chipped or cracked NMR tubes.
  • Use 507PP or 528PP NMR tubes on the Varian instruments to prevent damage to the probes
  • Always use new 528PP NMR tubes for VT work. Old tubes my be scratched and more likely to break.
  • All users must abide by the scheduling restrictions.
  • All users must sign the spectrometer log book.
  • All users must lock and shim the standard sample with finished using the spectrometer.

Scheduling:

Scheduling time on the hands-on NMR instruments is done through the web scheduling program. While scheduling time, if the computer program does not reserve the time you requested, chances are you are trying to circumvent the rules.

NMR Experiments

General information

  • SENSITIVITY
    • Higher field gives better S/N, so 500 > 400 > 200MHz
    • Probes optimized for a particular nucleus give the best S/N for that nucleus. The VI-500 has two indirect detection probes and is thus most sensitive to proton. The VI-500, VI-400, and the VMVx-200 all have direct detection probes and give better S/N for other nuclei, e.g., carbon.
  • RESOLUTION and DISPERSION
    • Higher field spreads out the signal better, makes coupling patterns simpler, separates different signals better. Again, 500 > 400 > 200MHz.
  • Collection times
    The collection time for the following experiments assumes you are familiar with How to Run a 1-D Proton Spectrum, there are no NMR instrumentation HICCUPS and the proper probe is installed and tuned to the sample. For experiments with multiple pulses at a constant temperature the value of the 90 degree pulse (flip angle pw in micro sec.) is critical for success of the experiment. The 90 degree pulse width is duration of radio-frequency pulse at a given transmitter power (tpwr) that gives maximum signal from a single pulse. In practice, the 360 degree pulse width is the easiest to find and it is not as prone to artifacts. The 360 degree pulse width will be the null point going from negative to positive intensity with a proper relaxation delay (d1 in sec.).

Proton-detected experiments

  1. Availability
    • H1 experiments are available on all instruments.
  2. 1D Proton experiment
  3. COSY - Proton-proton correlation experiment
  4. NOESY - Proton-proton through-space interactions via NOE
  5. HMQC - Heteronuclear Multiple Quantum Correlation experiment
  6. HMBC - Heteronuclear Multiple Bond Correlation experiment

Carbon-detected experiments

  1. General
    • Availability
      • Probes optimized for X-nuclei give better S/N. All of our NMR systems have direct detection probes in; these probes give the best carbon S/N.
      • Sensitivity is approximately 5700 times less than for proton, so adequate S/N for a reasonable length experiment (10 minutes, 256 scans) requires a concentration of > 100mM.
  2. 1D Carbon experiment
  3. APT experiment
  4. DEPT experiment.
  5. HETCOR - Proton-carbon correlation experiment
  6. 2D-INADEQUATE

Phosphorus-detected experiments

  1. General
    • Availability
      • The VI-400 has a 4-nuclei probe capable of running phosphorus at any time. The VI-500 can run P31 with a probe change.
      • Sensitivity is approximately 15 times less than for proton, so adequate S/N for a reasonable length experiment (256 scans) requires a concentration of > 0.1mM.
  2. 1D Phosphorus experiment

Fluorine-detected experiments

  1. General
    • Availability
      • The VI-400 has a 4-nuclei probe capable of running fluorine at any time. The VI-500 can run F19 with a probe change
      • Sensitivity is approximately the same as for proton, so adequate S/N can be obtained with concentration > 0.1mM.
  2. 1D Fluorine experiment
The NMR Facility Manager can be reached at shirazi@chem.ucsb.edu