NMR spectrometers Fourier transform

Fig. 3. A block diagram schematic representation of a Fourier transform nmr spectrometer, ie, a superconducting magnetic resonance system.

Spectroscopic Analysis. Infrared (IR) spectroscopic analysis was performed on a Beckman Microlab 620 MX computing spectrometer. Samples were cast on a sodium chloride pellet or made into a pellet with potassium bromide. and 13C NMR spectra were obtained using a JEOL HNM-FX 270 MHz Fourier transform NMR spectrometer. Samples were dissolved in deuterium chloroform and chemical shifts were referenced to an internal standard of tetramethylsilane. 

The 13C NMR sensitivity can sometimes be a problem, but for the kind of samples studied here the effective concentration of monomer units is several molar which does not place excessive demands on present Fourier transform NMR spectrometers. In addition to the sensitivity of the chemical shift to structure (9), the relaxation of protonated carbons is dominated by dipole-dipole interaction with the attached proton (9). The dependence of the relaxation parameters T, or spin-lattice, and Tor spin-spin, on isotropic motional correlation time for a C-H unit is shown schematically in Figure 1. The T1 can be determined by standard pulse techniques (9), while the linewidth at half-height is often related to the T2. Another parameter which is related to the correlation time is the nuclear Overhauser enhancement factor, q. The value of this factor for 13C coupled to protons, varies from about 2 at short correlation times to 0.1 at long correlation... 

The NMR spectrum of calcitriol, recorded on a Varian XL-100/Nicolet TT-100 pulsed Fourier Transform NMR spectrometer, with internal deuterium lock, is shown in Figure 2 (2). The spectrum was recorded using a solution of 0.84 mg of sample dissolved in 50 microliters of CD OD (100%D) containing 1% v/v tetramethylsilane in a 1.7 mm capillary tube. The spectral assignments are given in Table I. 

H NMR has long been routinely used to detect the presence of M-H bonds and also to obtain structural information about clusters containing organic ligands. The availability of Fourier transform NMR spectrometers over the last few years has enabled studies involving 13C, 31P and other nuclei also to be carried out. This has made NMR an extremely useful technique for obtaining structural information and, be-... 

C NMR spectra were recorded on a JEOL Fourier Transform NMR spectrometer FX-90Q from samples in solutions in CDC13. 

All facets of study have been greatly aided by the ease with which crystal structures may be obtained and by the availability of sensitive Fourier transform NMR spectrometers which allow nuclei such as l70, 51V, wNb, s5Mo, and, K3W to be used for structural studies. Oxygen-17 NMR spectroscopy has proved to be particularly useful because 170 chemical shifts are very sensitive to environment. As a result it is possible to distinguish between terminal and various kinds of bridging oxygen sites. The l70 spectrum of [W Oi, ]2 and its structure are shown in Fig. Ifi-IOa/1 We see... 

The following are general notes and comments concerning the use of NMR specifically for common rubber characterization problems. A schematic of a Fourier Transform NMR spectrometer is given in Figure 8. 

The 1H NMR spectra of parbendazole was recorded with a JEOL-PS 100 NMR spectrometer operating at a frequency of 100 MHz and a magnetic field strength of 2.349 T. Spectra were determined over the region 10.8-0.0 parts per million (ppm), with a sweep time of 250 s. Chemical shifts were recorded as S (delta) ppm downfield from tetra-methylsilane (TMS). Proton noise and off-resonance decoupled 13C NMR spectra were measured on a JEOL FX 90Q Fourier Transform NMR spectrometer operating at 90 MHR and spectral width of 5000 Hz (220 ppm). All measurements were obtained with the compound being dissolved in deuterated dimethyl sulfoxide (DMSO-d6) for dT NMR and in deuterated trifluoroacetic acid (TFA-dx) for 13C NMR. 

The broad band decoupled carbon-13 NMR spectrum of cimetidine hydrochloride (Figure 3) was obtained by using a solution of approximately 100 mg/ml in deuterated dimethylsulf oxide. The deuterium signal of dimethylsulfoxide was used as the internal reference and the spectrum was obtained on a Varian Associates Model FT-80 fourier transform NMR spectrometer. The chemical shift assignments are ... 

Any modern Fourier transform NMR spectrometer manufactured in the 1980s by major instrument companies is capable of performing various types of H NMR experiments needed for studies of hemoglobin. With a modern 7.0-Tesla high-resolution NMR spectrometer operating at 300 MHz for H, a satisfactory H NMR spectrum (with a signal-to-noise ratio of 20 or better) of 0.3—0.5 ml Hb in millimolar concentration contained in a 5-mm sample tube can be obtained in a few minutes. 

FIGURE 3.15 Schematic diagram of a Fourier transform NMR spectrometer with a superconducting magnet.The probe is parallel with the z axis of the magnet, which is cooled with liquid helium surrounded by liquid nitrogen in a large Dewar flask. 

Total Carboxyl and Phenolic Hydroxyl Content Conductimetric titrations employed were modifications of the procedure described by Sarkanen and Schuerch (11) for lignin total phenolic content. Spectroscopic determinations on the phenolics and neutrals fractions were carried out using the JEOL FX-900 Fourier Transform NMR spectrometer and the Nicolet 5SXC Fourier Transform Infrared Spectrometer. In addition, the solid state CP/MAS 13C-NMR spectra were obtained by the Regional NMR Center at Colorado State University using conditions described in Bryson et al. (12). 

With the popularity of the pulse Fourier transform nmr spectrometers, recent CIDNP experiments were largely performed in a FT spectrometer. The technique has been reviewed by Kaptein (80), who has emphasized the important facts initially pointed out by Ernst et al. (55) in connection with using a FT spectrometer for CIDNP experiments. For homonuclear multiplet effects a small flip angle of less than 20° should be used to exhibit the multiplet features. As a 90° pulse turns the magnetization vector from the z axis to the xy plane, it would eliminate the homonuclear multiplet effects but not the net effects. The... 

The development of pulsed Fourier-transform NMR spectrometers has greatly increased the sensitivity of NMR measurements, allowing spectra to be obtained for and other nuclei at natural abundances and low sample concentrations. In this experiment this enhanced capability is utilized in a low-density gas-phase measurement of the equilibrium constant Kp for H-D exchange in the reaction... 

The temperature dependence of the NMR absorption in coals and pitches has been obtained by using a pulsed Fourier transform NMR spectrometer with a high-tempera-ture probe. With increasing temperature the value of the line width at half height of a brown coal decreases... 

All spectra were obtained using a Varian VXR 200 Fourier transformer NMR Spectrometer (18). The NMR spectra presented are consistent with the chemical structure of indapamide. 

Inspection of Eq. (6) reveals that it takes ca. 5.3 x Tx (the value of t when Mz = 0.995 M0 and Mt = 0) for the system to recover to within 0.5% of the Boltzmann equilibrium condition after the system has become saturated. It is for this reason that the duration between pulses in Fourier transform NMR spectrometers (most modem spectrometers) should be at least 5 x 7", for the production of quantitatively meaningful NMR spectra. 

Two-Dimensional Semiquantitative NMR. Spectra were collected on a Varian Unity 400 Fourier transform NMR spectrometer at 161.90 MHz. The phosphates were prepared at 3-5 weight per cent in water and a DjO insert used for locking purposes. Homonuclear 2DJ-resolved spectra were accumulated using an 8K X 0.2X data set with an acquisition time in the F dimension of 0.946 sec, four steady state pulses, 128 transients, and 200 increments in the F domain. Spectra were analyzed with zero-filling to 16K X 0.5K and application of a sine bell or shifted sine bell weighting function on a Sun Microsystems Sparc 1+ computer. 

Figure 15. Block diagram of pulsed Fourier transform NMR spectrometer (from [120]).

The NMR spectra on low molecular weight compounds were recorded on a Varian T-60A spectrometer. NMR of polymers were recorded on a JEOL JNM-FX902 Fourier Transform NMR Spectrometer equipped with a FAFT50 FG/BG disc unit, and WM-360 FT NMR spectrometer equipped with ASPEC 2000 computer system manufactured by Bruker Instruments, Inc. 

Stilbs, P. and Moseley, M.E. (1979) Nuclear spin-echo experiments on standard Fourier-transform NMR spectrometers - Application to multi-component self-diffusion studies. Chem. Scripta., 13, 26-28. 

A Varian XLFT-100 Fourier Transform nmr Spectrometer interfaced with a Varian 620-L minicomputer with magnetic tape storage provided high-resolution, proton-decoupled spectra of natural abundance carbon-13 at 25.2 MHz. For identification of carbon peaks, chloroform-d solutions of surfactant (solubility about 20 wt%) were prepared. Chloroform-d also served for a deuterium field lock. Samples of surfactant in water or decane were placed... 

The NMR experiments were performed at 60 MHz using the Bruker WP 60 pulsed Fourier transform NMR spectrometer. 

These early measurements stimulated my interest in NMR spectroscopy, and, on moving to the University of Kent at Canterbury (1972), we were lucky to be able to buy the first Fourier Transform NMR spectrometer in the UK. This instrument was still based on an electromagnet ( H, 100 MHz) but allowed faster acquisition of NMR spectra and enabled the development of multinuclear NMR spectroscopy. This permitted me to start collaborating with Paolo Chini who had taken up an appointment at the University of Milan where he was developing metal carbonyl cluster chemistry. In Milan, Chini had access only to an IR spectrometer that aided the clean preparation and subsequent crystallisation of clusters, and, importantly, an X-ray diffractometer for their structural characterisation. 

A. G. Redfield, "How to build a Fourier transform NMR spectrometer for biochemical applications" in Introductory Essays, edited by M. M. Pin tar (Sp ringer-Verlag, Berlin, 1976), pp. 137-152. 

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]. 

Cross polarization/magic angle spirming (CP/MAS) measurement (19) C NMR, Fourier transform NMR spectrometer at room temperature (1) and at 25 MHz. Internal standard tetramethylsilane and C and 2D-NMR, at 35°C in CDCI3 under a nitrogen (5)... 

S. Sasaki, Y. Hirota, S. Ochiai, and Y. Kudo, Bunseki Kagaku. 2/, 916 (1972), cf. Chem. Abstr.. 77. 100307p (1972). JAL-30XA is optional software availaUe for the JNM-FX60 Fourier Transform NMR Spectrometer equipped with a 16K minionnputer (JEOLCO, Ltd). 

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