Drying NMR tubes

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 

NMR tubes can be tested for camber and concentricity by using an NMR tube checker. These tube checkers are available from Wilmad and other vendors. 

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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 reaction of 2,2-dimethoxypropane with acid to form methanol and acetone can be followed by both proton and C NMR. Into a dry NMR tube, add 0.6 mL of 2,2-dimethoxypropane. Obtain the NMR spectrum and integration. Then add 0.1 mL of 1 M HCl and mix well for about 5 min. Obtain the NMR spectrum again, (a) Write out the reaction, using structures. Predict how many proton and/or carbon peaks you should see in the first spectrum. Predict how many peaks should be seen in the second spectrum, (b) Look up the chanical shifts of the protons (and C, if obtained) in the tables in the chapter and predict where each proton or carbon will be observed relative to TMS. (c) Confirm the identity of the peaks in your spectra. 

Poly(ethyl methacrylate) (Cellomer Associates) was vacuum dried at 50 C. The molecular weight (M ) was determined to be 3.3 X 10 from its intrinsic viscosity in ethyl acetate.— Chloroform (spectral grade) and deuterochloroform (MSD Isotopes) were used as received. Prior to sample preparation the solvent was degassed using five freeze-thaw cycles. The solvent was vacuum distilled onto the polymer In a 12 nm NMR tube, and sealed. 

All NMR spectra were recorded on a Varian A-60 spectrometer at room temperature by Nuclear Magnetic Resonance Specialties, Inc., New Kensington, Pa. Benzene soluble fractions were recorded in deuterated chloroform solution (CDCls) while dimethyl sulfoxide-dc (DMSO-dr.) was the solvent employed for other fractions. (Deuterated chloroform with enrichment of 99.8% was purchased from Bio-Rad Laboratories and dimethyl sulfoxide-dr, with enrichment of 99.6% from Merck, Sharp, and Dohme of Canada.) The internal standard used with the CDCla solutions was tetramethvlsilane and hexamethyl-disiloxane (chemical shift 7 c.p.s.) with DMSO-d . Prior to preparation for NMR recording, the samples were thoroughly dried in a vacuum at 110°C. The NMR tubes were sealed to minimize the absorption of atmospheric moisture. The chemical shifts given in c.p.s. are referred to tetramethylsilane. 

A dry environment is required for the final tempering stage as liquid water on the outside of the NMR tube can be transferred to the coil and bias the measurement (as well as subsequent measurements taken from the contaminated coil). If a dry tempering block is unavailable, it may be possible to use a water bath if rapid and complete drying of the tube can be achieved before significant temperature drift has occurred. 

Fig, 9.34, Apparatus used for the preparation and sampling of Grignard reagents for NMR spectroscopy. The apparatus was evacuated through J2 and the Mg baked. Excess ether and alkyl halide were distilled onto the metal, and the apparatus was sealed off at S3. Upon warming to 0°C and shaking, a rapid reaction occurred. The apparatus was evacuated at Jj, the break-seal B was broken, and ether and excess alkyl halide were removed. Fresh dry ether and the letramethyl silane standard were distilled in, the apparatus was sealed off at S, and a small portion of the solution was filtered through the frit F into the NMR tube, which was sealed off at S2. (Adapted from D. F. Evans and J. P. Mahler, / Chem. Soc.t 1962, 5125.)... 

Figure 3 Liquid crystalline (A) and gel-based alignment medium (B) at various stages (A) dry PBLG and the readily prepared lyotropic mesophase. (B) Cross-linked PS as an unswollen polymer stick in a standard NMR tube (left), polymer stick directly after polymerization, fully swollen polymer stick, polymer stick swollen in an NMR tube with an effective stretching along the tube axis (right). (Reproduced from refs. 17 and 53 with permission from Wiley-VCH Verlag GmbH Co. KGaA (Copyright).)...

The ferrous porphyrins were reoxidized by introducing oxygen into the NMR tube of the autoreduced sample. To detect water as a product of the reoxidation of TPPFen(CN)22", it was necessary to completely exclude the possibility of atmospheric contact (dry DMSO rapidly absorbs water from the atmosphere). These experiments were done in an NMR tube fitted with a ground glass stopcock. This allowed the addition of oxygen into the NMR tube by vacuum line techniques, completely eliminating atmospheric contact. Experiments done on blanks of dry DMSO showed no water peak. 

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... 

Thin films of polymer were placed into four sterilized NMR tubes containing D2O and D2O buffered at pH=4, pH=7 and pH=9. NMR tubes were immediately sealed and placed in a drying oven at 37°C and analyzed at different degradation times. 

FIGURE 2.21 NMR solid-state spectra of (a) a-chitin from deproteinized lobster tendon, (b) p-chitin from dried deproteinized tube of Tevnia jerichonana. 

All reactions and sample preparations are carried out in an inert-atmosphere enclosure under dry nitrogen. Solvents and reagents are dried in the following manner. Benzene, tetrahydrofuran, and n-pentane are freshly distilled from lithium aluminum hydride pyridine is distilled over barium oxide and tetramethylethylenediamine is distilled over calcium hydride. Solvents used in preparing nmr and infrared samples are degassed by a freeze-thaw technique. Nmr spectra are obtained with torch-sealed nmr tubes. The commercial transition metal carbonyl complexes are recrystallized and vacuum-dried before use. Glassware is routinely flame-dried. 

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