Instrumentation

FT-NMR

Sample Preparation

The Reed College FT-NMR is an extremely sensitive instrument. Therefore, it is important not to put too much compound in your NMR tube.

It is also important to put the right amount of solvent in the NMR tube. Too much solvent will dilute your compound too much and keep the tube from spinning. Too little solvent will force the vortex (created by the tube’s spinning motion) into the sampling zone and ruin your NMR measurements.

To make an NMR sample for a liquid compound:

  1. Obtain a clean 5 mm NMR tube and two clean disposable pipettes.
  2. Briefly dip the tip of one pipette into your liquid (do not attach a bulb to the pipette). Capillary action will cause some liquid to enter the pipette tip.
  3. Insert the moistened pipette tip into the NMR tube so that the pipette rests inside the tube.
  4. Draw ~0.5 mL of NMR solvent into the second pipette and squirt this into the top of the pipette holding your compound. This rinses the compound down into the NMR tube. If necessary, add enough solvent so that the column of liquid in the NMR tube is 4-6 cm high.
  5. Cap your tube securely.
  6. Make a label for your tube that identifies you, your lab day, and the sample. Attach the label to your tube. Labels will usually follow this format: EXP-DAY-INI where ‘EXP’ is a three-letter code for the experiment or sample (use ‘BAN’ for banana oil), ‘DAY’ is a three-letter code for your lab day (TUEWED, THU or FRI) and ‘INI’ is a three-letter code containing your initials. Write your label in your lab notebook.
  7. IMPORTANT – Holding your tube by the cap, wipe the entire tube with a clean Kimwipe to remove fingerprints, oils, etc., and deposit your tube in the labeled collection beaker. Our NMR instrument is easily damaged by substances clinging to the outside of the tube. If you should happen to forget and touch your tube (or any other student’s tube) for some reason, wipe down the entire tube again and place it in the labeled beaker.

These instructions can be used with nearly any NMR solvent, but nearly all samples in Chem 201/202 are made using CDCl3 (deuterochloroform) impregnated with a small amount of (CH3)4Si, which is also known as TMS (tetramethylsilane). CDCl3 is a highly volatile cancer suspect agent; do not remove it from its fume hood. TMS is even more volatile, so please keep the lid on the bottle as much as you possibly can or this expensive reagent will quickly be ruined.

Printing your FT-NMR spectrum

The measurement of an NMR spectrum generates a set of data files that need to be downloaded and converted into graphs suitable for interpretation. Instructions for downloading the data files, and for printing NMR spectra as PDF documents using MestReNova are provided in Appendices: MestReNova.