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.
How to make an NMR sample for a liquid compound
- Obtain a clean 5 mm NMR sample tube and two clean disposable pipettes.
- 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.
- Insert the moistened pipette tip into the NMR tube so that the pipette rests inside the tube.
- Draw approximately 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.
- Cap your tube securely.
- Holding your tube by the cap, wipe the entire tube with a clean Kimwipe and methanol to remove fingerprints, oils, etc. Our NMR instrument is easily damaged by substances clinging to the outside of the tube.
- Make a label for your tube that identifies you, your lab day, and the sample. Write your label in your lab notebook.
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.
Generating 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.