Magnetogyric ratios

Because J arises from the magnetic interactions of nuclei, the simplest factor affecting it is the product yjY of the two nuclear magnetogyric ratios involved. For example, in FI F is 82 FIz, i.e. x yo/yf - This totally predictable factor is sometimes discounted by quoting the reduced coupling constant =... 

The equation describes the manner in which the nuclear magnetization, M, at position r and time t processes about the magnetic flux density, B, in which it is found. The constant y is the magnetogyric ratio of the nuclides under study. The precessional frequency, co, is given by the Lannor equation. 

Carbon-13 nmr. Carbon-13 [14762-74-4] nmr (1,2,11) has been available routinely since the invention of the pulsed ft/nmr spectrometer in the early 1970s. The difficulties of studying carbon by nmr methods is that the most abundant isotope, has a spin, /, of 0, and thus cannot be observed by nmr. However, has 7 = 1/2 and spin properties similar to H. The natural abundance of is only 1.1% of the total carbon the magnetogyric ratio of is 0.25 that of H. Together, these effects make the nucleus ca 1/5700 times as sensitive as H. The interpretation of experiments involves measurements of chemical shifts, integrations, andy-coupling information however, these last two are harder to determine accurately and are less important to identification of connectivity than in H nmr. 

Other Nuclei. Although most nmr experiments continue to involve H, or both, many other nuclei may also be utilized Several factors, including the value of I for the nucleus, the magnitude of the quadmpolar moment, the natural abundance and magnetogyric ratio of the isotope, or the possibihty of preparing enriched samples, need to be considered. The product of the isotopic parameters can be compared to the corresponding value for providing a measure of relative sensitivity or receptivity. Table 1 summarizes these factors for a number of isotopes. More complete information may... 

A nucleus having spin generates a magnetic moment pi. which is proportional to the angular momentum. Theory is not capable of calculating pi, so it is commonly expressed as Eq. (4-42), where 7 is called the magnetogyric ratio. 

The angular momentum is related to the moment by the magnetogyric ratio. 

Receptivity D is proportional to y NKJ + 1) where y is the magnetogyric ratio, N the natural abundance of the isotope, and / the nuclear spin quantum number Dp is the receptivity relative to that of the proton taken as 1.000. 

Another separation method in using nonselective relaxation-rates is based on deuterium substitution, and utilizes the fact that the efficiency with which a nucleus contributes to the relaxation of a neighboring nucleus is proportional to the square of the magnetogyric ratio of the donor nucleus, that is, Phd/PHH = /3(yo/yn) - Because yo/yn — l/, replacement of a proton by a deuterium nucleus would be expected to contribute to the... 

Magnetogyric Ratios of Some Important NMR-Active Nuclei... 

What is the magnetogyric ratio, and how does it affect the energy difference between two states and the nuclear species sensitivity to the NMR experiment ... 

No. Since the magnetogyric ratio of C is roughly one-fourth that of H, the population difference between the two states (a and )3) of C nuclei will therefore be about 64 times [(1/4) = 1/64] less than that of the H nuclei. 

The sensitivity enhancement in the INEPT experiment is particularly marked when nuclei of low magnetogyric ratios are being detected. A comparison of the signal intensities obtained by polarization transfer against those obtained by full NOE for various nuclei is presented in Table 2.1. 

Transfer of polarization from C nuclei to H nuclei and their subsequent detection leads to a 16-fold increase in sensitivity because the C magnetization is being measured indirectly through detecting it via the nucleus with the higher magnetogyric ratio (i.e., H). Irradiation of the protons between the scans causes a further threefold increase in the population of the C nuclei due to nOe, so an overall 50-fold increase in sensitivity is achievable in contrast to direct C measurements. However, because of... 

Polarization transfer Application of certain pulse sequences causes the transfer of the greater-equilibrium polarization from protons to a coupled nucleus, e.g., C, which has a smaller magnetogyric ratio. 

Fig. 42a-c Spectra of tetramethyltin in CDC13. a Proton decoupled, b proton coupled (2JsncH 54.3 Hz), c proton spectrum. The satellite signals are due to coupling to tin-117 (inner lines) and tin-119 (outer lines). The ratio of the coupling with tin-119 to that with tin-117 is 1.046 1 (the ratio of the magnetogyric ratios of the two nuclei)... 

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