Cleaning, NMR tubes

Clean, high-resolution NMR tubes quality of the tube is determined by the field strength of the magnet (5 mm OD for proton, 10 mm OD for carbon-13)... 

NMR tubes are thoroughly cleaned by successive washing with acetone and distilled water and subsequently dried in an oven All metal ion-containing cleaning solutions should be avoided... 

Make sure you use thoroughly cleaned and dried NMR tubes, and never assume that a new tube, fresh out of the box, is clean to NMR standards. 

The solution used must be free of paramagnetic metal ions (it usually is) and particles (it usually is not). Place sufficient sample into a clean, small, vial (weigh it in if you are unsure how much to use), add the solvent (ca. 0.5ml) to dissolve the sample. After taking up this solution into a Pasteur pipette, filtration through a small wad of cotton wool forced into a Pasteur pipette, directly into the nmr tube will usually remove sufficient particles to allow a good spectrum to be obtained. Be very careful that no... 

Cleaning Up Place the contents of the nmr tube in the europium shift reagent hazardous waste container. 

In a typical experiment 80 mg of FS03H was introduced into a dry clean proton NMR tube at -115° followed by condensation of SOjCIF ( 0.35 ml). With the aid of a cooled glass rod 30 mg of precursor was introduced and the resultant mixture homogenized. Appropriately larger amounts were used for the 13C NMR than for the H NMR spectra. Immediately after the generation of the cations the samples were inserted into the precooled NMR probe. The temperatures at which the spectra were recorded were measured using... 

Upon completion of the desired reaction the flame-sealed NMR tube is placed in the apparatus shown in Figure 2. The NMR tube must be scored and the score aligned with the stopcock A to insure a clean break of the tube (See Figure 2). The setup is then evacuated on a vacuum line while the contents of the NMR tube are cooled with liquid nitrogen (the tube is cooled to prevent rapid escape of the volatile materials upon exposure to the vacuum). Once evacuation of the apparatus is complete, stopcock B is closed and the sealed NMR tube is cracked by turning... 

Whenever we use a tube—even for the first time—we may wish to wash it out thoroughly. If rinsing with appropriate solvents fails to properly clean an NMR tube, the tube may not be visually free of residue. That is, it will appear cloudy or translucent instead of transparent. Immersion of the tube for 30 seconds in a saturated base and alcohol bath may suffice. Caution when we perform this step, we wear gloves, a laboratory coat or an apron, and safety glasses or a face shield—we are only born with, after all, one perfect suit of skin and one set of eyes, hands, and feet. 

Sometimes physical abrasion is needed to properly clean a tube. In this case, we GENTLY scrub the inside and outside of the tube. We can use pipe cleaners to clean 5 mm NMR tubes effectively, but we must take care not to scratch the inside of our tube rvith the exposed wire at the end. 

We dry expensive (and, most properly, all) tubes by laying them flat on a paper towel or clean cloth. We never store NMR tubes upright inside a beaker or an Erlenmeyer flask, and never put tubes in a diying... 

The [2+2+2+1] cycloaddition reaction of dodeca-5,10-diyn-l-al 220 carried out with [Rh(cod)Cl]2 (5 mol%) at 50°C and ambient pressure of CO in toluene gave cycloadducts 221 and 222 (65% combined yield) as well as acetyl-bis(cyclopentenyl) 223 from the [2+2+2] cycloaddition in 33% yield. Upon monitoring the reaction, it was found that fused 5-7-5 tricyclic lactone 221 was the kinetic product and the clean and complete isomerization of 221 to 222 was observed by leaving a mixture of 221 and 222 in CDCI3 in an NMR tube for 2 weeks at ambient temperature (Scheme 99). 

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