13C magnetization

Gruetter, R., Novotny, E. J., Boulware, S. D. etal. Non-inva-sive measurements of the cerebral steady-state glucose concentration and transport in humans by 13C magnetic resonance. In L. Drewes and A. Betz (eds), Frontiers in Cerebral Vascular Biology Transport and its Regulation, vol. 331. New York Plenum Press, 1993, pp. 35-40. 

The simplest double tuned filter can be constructed by a concatenation of two X-half filters and removal of redundant 180° pulse pairs (Fig. 17.4d) [22]. Alternatively, it can also be realized by keeping the 180° pulse pairs and adding short spin-lock periods (to dephase the 1H-13C magnetization which is orthogonal to the spin-lock axis, Fig. 17.4e) [23], or it is based on the gradient-purging scheme of Fig. 17.4b, resulting in the double filter shown in Fig. 17.4f [18]. 

The 13C magnetic resonance spectra have been reported for naturally occurring nucleotides 538, nucleosides,79-81,539 and uracil, thymine, 5-... 

Fig. 2.51.. /-Modulated spin-echo sequence with gated proton decoupling for acquisition of -/-resolved two-dimensional 13C NMR spectra, and the CH magnetization vectors in the x y plane controlled by pulses and. /-modulation. During the preparation period between successive experiments, nuclear Overhauser enhancement of 13C magnetization is retained by minimum proton decoupling.

Table 10 Representative calculations of 13C magnetic shielding constants relative to 13C in CH4 calculated using SCF perturbation theory and GIAO...

On the subject of carbon aromaticity of coal, 13C magnetic resonance spectroscopy has also found use in determining the fraction of carbon atoms that are in aromatic locations (fa) as well as attempting to define the structure of the aromatic ring system. However, there is a possibility of serious underestimation of aromaticity by this method (Miknis, 1988 Snape et al., 1989 Sfihi and Legrand, 1990). 

In Fig. 1, the pulse sequences frequently used in this work are schematically shown. The pulse sequence I is used for obtaining DD/MAS 13C NMR spectrum without the CP procedure. The 13C magnetization which appears in the Bo direction for a time of T is turned through 90° by a resonant field and the free induc-... 

The 13C magnetic resonance spectrum is given in Figure 4 and was obtained using a Varian CFT-20 (FT mode) spectrometer with dgDMSO as the solvent at a concentration of 10% w/v. The spectrum is consistent with the structure and the assignments are in Table II (17). 

WISE NMR spectra are recorded using very short contact times in order to ensure that only the directly bound protons contribute to the 13C magnetization and influence of H spin-diffusion is eliminated. The WISE... 

Although dianion [Rh fCOu,]2 " has never been isolated in the solid state owing to its lability, it can be considered a definite intermediate. In fact, it has a characteristic and reproducible lit spectrum, and at — 70°C it has a peculiar 13C magnetic resonance spectrum consisting of two doublets (191.7 and 208.3 ppm) and a multiplet (247 ppm) (74). 

SXIZ, 2Sy lz S (13C) magnetization in the x -y plane, antiphase with respect to the z orien-... 

This is just following the rules for each individual operator in the product (Fig. 7.15). The resulting product operator, 2SXIZ, can be described as 13C magnetization on the xf axis, antiphase with respect to the z magnetization (a or p state) of its attached H nucleus. Acquisition at this time would yield an FID at the 13C frequency, and Fourier transformation with phase reference - -x would give a carbon doublet with a downfield component of normal phase and an upheld component of opposite phase (upside-down). This is what you will see in your INEPT spectrum an antiphase 13 C doublet. Later, we will see that this spectrum is actually four times as intense as the normal 13C spectrum this is the enhancement part of INEPT. 

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