Proton magnetic resonance spectra parameters

Fig. 14. (a) Relative values of the local magnetic fields at H4, H5A and H5B protons belonging to water molecules and (b) the width of the proton magnetic resonance spectrum, in a TmES crystal at 4.2 K (Egorov et al. 1984b). The external field Ho is perpendicular to the c-axis (f) is the angle of Hq with the a-axis solid lines are the results of calculations with the lattice parameters Oo = 13.59A, Co = 6.86A the dashed line is calculated using the YES lattice parameters. 

Fig. 3.—Fourier-transform, Proton Magnetic Resonance Spectra45 of 6-Deoxy-l,2 3,4-di-O-isopropylidene-6-phthalimido-a-D-gaIactopyranose (54) (0.06 mg) at 90 MHz, Obtained by Transformation (N = 4,096) of the Free-induction Decay Signal (1,024 Datum Points, see Fig. 2), After the Appendation of 3,072 Zero, Datum Points ( Zerofilling, See Text), [(a) Spectrum associated with the real part of the transform, and (b) with the imaginary part (c) absorption-mode spectrum computed by phase correction of the spectrum in (a) and (d) dispersion-mode spectrum computed by phase correction of the spectrum in (b). Parameters for phase correction, A —255° and B —215°. Note that the phase of the tetramethylsilane and chloroform signals in (c) is slightly different from that of the carbohydrate derivative. By coincidence, the peak for residual water in spectrum (c) has almost the same intensity as the methyl signals, and could have been mistaken for one, had other spectra not been recorded.]...

The NMR spectrum of pyridazine shows two symmetrical quartets of A2X2 type and t values and coupling constants are as follows Te = 0.76, T4 = T5 = 2.45 t/3 4 = /5,e = 4.9 (5.05 ),. Ig 5 = 7 4,6 = 2.0, Jg g = 3.5 (1.4 ), J4 5 = 8.4. The C satellites in natural abundance in the liquid state have been examined in order to obtain a complete set of proton magnetic resonance parameters for pyridazine. It has been found that chemical shifts are strongly concentration-dependent in a sense opposite to that normally found with aromatic compounds. Coupling constants are, however, virtually invariant. From the NMR spectrum, a deshielding effect on the hydrogen atoms at positions 3 and 6 is revealed. ... 

Optical detection of magnetic resonance (ODMR) was attempted for measurements of the pH effects on the triplet state of purine to investigate the protonation site of purine at low temperatures (78JA7131). The ODMR spectrum did not show the presence of more than one triplet state at liquid helium temperatures. Since the protonated tautomers 1H,9H (3a) and H,1H (3b) have similar bond structures, their triplets should have similar zero-field parameters and are thus not easy to distinguish by ODMR. 

Boum describe their use of the line shape method in the temperature range —24° to — 82°C (deuterium decoupling was used so that only the unperturbed single proton resonance was observed) and of a double-resonance method in the temperature range —97° to — 116°C. This involved the observation of recovery of magnetization of one of the two lines in the spectrum after a saturating r.f. field applied to the other line was removed. Consistent rates of inversion were found from both methods as evidenced by linearity of the Arrhenius plot. The results do not agree with the spin-echo results of Allerhand et al In this type of work, while fairly consistent results of rate constants may be obtained, there is dispute as to how the thermodynamic parameters should be derived, even in the relatively simple case of cyclohexane. ... 

As a result of the field modulation and the phase-sensitive detection, the spectrum is recorded as the first derivative of the absorption, with the x-axis synchronized to the magnetic field that is swept across the resonance. For accurate measurements of the resonance parameters it is customary to calibrate the field, either with a field meter based on proton NMR, or to use a standard sample with known g-factors and hyperfine splittings. The microwave frequency is measured with a frequency meter attached to the microwave bridge. Modem instruments are computer controlled spectra with instrument parameters are saved and stored digitally. 

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