T inversion recovery

The T, Inversion-Recovery experiment is not restricted to C nuclei, but may also be applied to other nuclei, e.g, protons. In this case, the pulse sequence for the observe channel is the same, but no broadband decoupling is used. 

Fig. 3.19 Stacked plot of a C T, Inversion-Recovery experiment with peracetylated...

Calculate the T, values for the carbonyl carbons of the oligosaccharide. Load the raw data of the pseudo 2D C T, inversion recovery experiment D NMRDATA OLIGOSAC 1D C OCT1 2D 001001.SER. Decompose the 2D data matrix into a series of 1D FIDs, process and plot them according to the recommendations given in previous chapters. Exploit the options for automatic and serial processing. Determine the T, values for the individual carbon nuclei using the interactive fit routine of ID WIN-NMR. Use the Help information if necessary. 

The vd command can be used for variable delays which cannot be expressed by simple arithmetic calculations as in a kinetic experiment or a T inversion recovery... 

T, Measurements. Ti values for the mobile domain carbons were measured using a (l80 -t-90 -T) inversion recovery pulse sequence (77) with continuous proton saturation. The optimum 180 pulse width was determined prior to each set of measurements. The time between pulse sequences was 2 s at 21 kG and 3 s at 47 kG. Measurements were generally made for 10-12 values of t which ranged from 0.005 s to T. Both integrated peak intensities and peak heights were used for the analysis of each T) data set equivalent results were obtained in both cases. 

Fig. 8.4 Spin—lattice (T ) inversion recovery pulse sequence. The 180° pulse inverts magnetization, allowing it to recover along the z-axis. The duration of the delay, r, is varied from T to several times the longest expected T relaxation time in the molecule. The resulting.

I and the measured line intensities are fitted to an exponential expression. S (-e) =A + B exp(-i / T ). The inversion-recovery experiments are often perfonned for multiline spectra of low-natural abundance nuclei,... 

Figure 2.27. Sequence of measurements to determine the C spin-lattice relaxation times of 2-octanol (42) [(CD3)2C0, 75% v/v, 25 °C, 20 MHz, inversion-recovery sequence, stacked plot]. The times at which the signals pass through zero, xo, have been used to calculate, by equation 10, the T values shown above for the nuclei of 2-octanol...

The most popular, and also a very accurate, experimental method for measuring nonselective spin-lattice relaxation-rates is the inversion recovery (180°-r-90°-AT-PD)NT pulse sequence. Here, t is the variable parameter, the little t between pulses, AT is the acquisition time, PD is the pulse delay, set such that AT-I- PD s 5 x T, and NT is the total number of transients required for an acceptable signal-to-noise ratio. Sequential application of a series of two-pulse sequences, each using a different pulsespacing, t, gives a series of partially relaxed spectra. Values of Rj can... 

Another method used to measure relaxation rates is the three-pulse (180°-t-90°-AT-PD—90°)nt sequence. This method is similar to the inversion recovery, with the addition of a third 90° pulse after the pulse... 

The 50.31 MHz 13C NMR spectra of the chlorinated alkanes were recorded on a Varian XL-200 NMR spectrometer. The temperature for all measurements was 50 ° C. It was necessary to record 10 scans at each sampling point as the reduction proceeded. A delay of 30 s was employed between each scan. In order to verify the quantitative nature of the NMR data, carbon-13 Tj data were recorded for all materials using the standard 1800 - r -90 ° inversion-recovery sequence. Relaxation data were obtained on (n-Bu)3SnH, (n-Bu)3SnCl, DCP, TCH, pentane, and heptane under the same solvent and temperature conditions used in the reduction experiments. In addition, relaxation measurements were carried out on partially reduced (70%) samples of DCP and TCH in order to obtain T data on 2-chloropentane, 2,4-dichloroheptane, 2,6-dichloroheptane, 4-chloroheptane, and 2-chloroheptane. The results of these measurements are presented in Table II. In the NMR analysis of the chloroalkane reductions, we measured the intensity of carbon nuclei with T values such that a delay time of 30 s represents at least 3 Tj. The only exception to this is heptane where the shortest T[ is 12.3 s (delay = 2.5 ). However, the error generated would be less than 10%, and, in addition, heptane concentration can also be obtained by product difference measurements in the TCH reduction. Measurements of the nuclear Overhauser enhancement (NOE) for carbon nuclei in the model compounds indicate uniform and full enhancements for those nuclei used in the quantitative measurements. Table II also contains the chemical... 

T, values can be easily determined using pulse sequences which form part of the standard computer software, the most common one being the so-called inversion-recovery experiment. 

MHz, solvent CDC13 (degassed) T ] determination of the carbon atoms by inversion recovery experiment selected 13C spectra... 

In some cases, CP is not necessary to obtain a suitable solid state NMR spectrum. In these cases, the SPE/MAS sequence may be used and for quantitative analysis only the X-nucleus T time needs to be determined. The standard inversion-recovery experiment (Fig. 10C) can be used to measure this... 

Because the excitation/detection coil is in the x-y plane and the longitudinal component relaxes along the z axis, T cannot be measured directly from an NMR spectrum, but must be obtained using a pulse sequence. The most commonly used pulse sequence to measure T is an inversion recovery pulse sequence (Kemp, 1986). Other commonly used pulse sequences for measuring 7j are given in Ernst et al. (1987). 

Ti measurements were performed at 250, 275 and 300 K by inversion-recovery (7r-T-7r/2-5T i) sequences on a JE0L-FX-100 and a Bruker WP-80 spectrometers. On this latter the "repetitive frequency shift" method of Brevard et al. (18) was used, where two systematic instrumental errors (drift, round off errors in FT processing.. .) are uniformly distributed through all data points. The NOE measurements are reproducible within 10-20 %, while the average standard error on the Tj values is of about 5 %. 

Longitudinal relaxation times (T]) and NOE measurements The relevant data are reported in Table III. The T values were measured by the inversion-recovery method. 

A number of pulse-sequence methods are available for measurement of Ti values, and those most commonly used are the methods of saturation recovery (s.r.F.t.),69,70 progressive saturation (p.s.F.t.),71 inversion recovery (i.r.F.t.),72 and the Freeman-Hill modification of in-... 

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