Nuclear magnetic resonance deuterated solvents

Halcinonide dissolved in either methanol, deutero-methanol, aqueous ammonia-methanol, or deuterium oxide deuter-ated ammonia-methanol solvents appears stable after storage for six days at 50°, using nuclear magnetic resonance and mass spectrometry.70... 

The nuclear magnetic resonance spectrum of valproic acid as shown in Figure 4 was obtained on a Varian Associates T-60 NMR Spectrometer as a 10% w/v solution in a solvent of deuterated chloroform. The spectral peak assignments (2) are presented in Table II. 

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. 

Copolymer compositions were determined by a high resolution nuclear magnetic resonance spectrometer (180 HMz). Copolymers of methyl methacrylate and styrene were dissolved in deuterated chloroform for the analysis. Deuterated pyridine was the solvent for the methyl methacrylate - methacrylic acid copolymers. Elemental analysis was also used in copolymer composition analysis to complement the NMR data. 

A separate section will be devoted to covering the monitoring of reaction progress at high pressure by nuclear magnetic resonance (NMR) spectroscopy. Although there have been no reports to date, in principle for sufficiently slow reactions aliquot samples from a piston-cylinder apparatus could be followed by NMR spectroscopy however, such a procedure would not be viable because of the large solution volumes required if deuterated solvents were to be used. 

Deuteration and trittation.7 Labeled trifluoroacetic acid has some advantages for deuteration and tritiation. It is obtained in quantitative yield by mixing trifluoroacetic acid and labeled water. It has excellent solvent properties and also functions as the acid catalyst. The uptake of label can be followed by nuclear magnetic resonance the reagent is readily removed by evaporation in vacuo. In the case of olefins, addition to form the trifluoroacetate occurs simultaneously. It lias been used for the labeling of A8- and A9-tetrahydrocannabinol. 

The nuclear magnetic resonance (NMR) spectra were recorded on a Varian A-60 spectrometer, using deuterated dimethyl sulfoxide (DMSO) as solvent and tetramethylsilane as internal standard. IR spectra were obtained on a Perkin-Elmer 237B IR spectrophotometer. 

Nuclear Magnetic Resonance Spectroscopy. Like IR spectroscopy, NMR spectroscopy requires little sample preparation, and provides extremely detailed information on the composition of many resins. The only limitation is that the sample must be soluble in a deuterated solvent (e.g., deuterated chloroform, tetrahydro-furan, dimethylformamide). Commercial pulse Fourier transform NMR spectrometers with superconducting magnets (field strength 4-14 Tesla) allow routine measurement of high-resolution H- and C-NMR spectra. Two-dimensional NMR techniques and other multipulse techniques (e.g., distortionless enhancement of polarization transfer, DEPT) can also be used [10.16]. These methods are employed to analyze complicated structures. C-NMR spectroscopy is particularly suitable for the qualitative analysis of individual resins in binders, quantiative evaluations are more readily obtained by H-NMR spectroscopy. Comprehensive information on NMR measurements and the assignment of the resonance lines are given in the literature, e.g., for branched polyesters [10.17], alkyd resins [10.18], polyacrylates [10.19], polyurethane elastomers [10.20], fatty acids [10.21], cycloaliphatic diisocyanates [10.22], and epoxy resins [10.23]. 

Lock or field/ A method for accurately maintaining frequency lock (locking) the static magnetic field at a fixed value. The frequency of a nuclear magnetic resonance signal - commonly deuterium from a deuterated solvent - is held at constant value by a field/fre-quency feedback loop to compensate for any magnetic field drift during an experiment. 

LC-nuclear magnetic resonance (NMR) One information-rich spectral technique that is more suited to the liquid mobile phase of HPLC than to the vapor phase of GC is NMR. LC-NMR has been implemented, but it has significant limitations. To obtain interpretable spectra of unknowns, concentrations in the measurement cell must be higher than with other detectors. The cell must be smaller than the usual NMR tube, so for any but the very highest concentrations of analytes, FT-NMR acquisition is preferred, with each eluted peak being retained in the measmement cell by a stopped-fiow procedme similar to that employed to increase sensitivity in GC-IR (Section 12.8.2). Expensive deuterated mobile-phase solvents are required for proton NMR, which mandates the use of low mobile-phase volume flow columns narrow-bore or even capillary HPLC. LC-NMR is expensive to implement and only just becoming available from commercial vendors at this time. 

The chemical structures of D-A alternating copolymers are routinely characterized by nuclear magnetic resonance (NMR) spectroscopy. Again, since the polymer chains need to be properly solvated and dispersed to expose all of the characteristic protons, higher temperatures near 100 °C are necessary. Therefore, deuterated solvents with high boiling points, such as 1,1,2,2-tetra-chloroethane-D2 (C2D2CI4), are typically used. 

Nuclear Magnetic Resonance Spectroscopy ( H NMR and NMR) Proton and carbon nuclear magnetic resonance sp>ectra (iH NMR and NMR, respectively) were obtained in a polynuclear JEOL Eclipse Plus 400 sp>ectrometer (400 MHz), using tetramethylsilane as the reference and deuterated chloroform and carbon tetrachloride as the solvent for NMR and iH NMR, respectively. i3C NMR spectrum were accumulated during 24 hours. 

Nuclear magnetic resonance (NMR) (see Chapter 10) Although stopped flow and online results have been published, SEC-NMR coupling is still not a standard technique [2]. The use of deuterated solvents or the need to suppress the intense solvent signals by special NMR pulse sequences has limited the applicability. An additional problem is the low sensitivity of NMR in combination with the low concentrations used in SEC. 

Nuclear Magnetic Resonance (NMR) methods have somewhat limited application to CPs, due to requirements for solubility or constraints magic angle spinning (MAS) or other adaptations to solid-state methods. Proton and C solution NMR are of course confined to the soluble, de-doped forms of CPs, in solvents such as CDCI3, and deuterated dimethyl formamide. Solid state methods have been applied with some success primarily to P(Ac). And nutation NMR studies have yielded some useful bond length information. Besides the illustrative studies cited below, many studies using NMR of CPs in conjunction with other analytic techniques for structural elucidation abound [410, 439, 440]. 

Besides FT-IR spectra, nuclear magnetic resonance (NMR) spectra, in particular, proton NMR ( H NMR) spectra are also frequently used to characterize PBI structure if the polymer is soluble in an appropriate deuterated solvent. Figure 8.21... 

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