Nuclear magnetic resonance second moment

As with graphite oxide, there are currently two views as to the structure of carbon monofluoride. Although detailed X-ray diffraction work suggested a chair arrangement of the sp -hybridized, carbon sheets (Ml), second-moment calculations of the adsorption mode of the fluorine nuclear magnetic resonance suggested that a boat arrangement is more plausible iE2). The structures are illustrated in Fig. 3. 

Only the diamagnetic susceptibility and the second moment of the nuclear magnetic resonance show additive molar properties. 

Although evaluations of harmonic force constants [d E dq,dqj), elearic polarizabilities d EIdeide ), and dipole moment derivatives (d E/d ,dqj) are perhaps the most common applications of second-order properties (or, equivalently, second derivatives), other areas of interest to chemists can be treated with these techniques. One such field of application that holds great promise for the future is the calculation of nuclear magnetic resonance chemical shifts. 

D. C. Look and I. J. Lowe, "Effect of hindered molecular rotation between unequal potential wells upon nuclear magnetic resonance spin-lattice relaxation times and second moments,"... 

Nuclear magnetic resonance data on cyclohexane are reproduced together with heat capacity information in Fig. 3.2. The transition parameters are listed in Table 3.1. Below 150 K the experimental proton NMR second moment of 26.0 + 0.5 G corresponds to that calculated for a crystal of rigid molecules of Djj dymmetry in the chair conformation. The decrease in secoixi moment from 155 to 180 K is caused by jump-reorientation about the triad axis with a 46 kJ/mol activation energy. The experimental second moment somewhat below T of 6.4 G corresponds to the calculated value of 6.1 l.OG for such motion. At the transition the ond moment drops to 1.4 G which is in line with additional reorientation about aU other axes (1.3 to 1.1 G calculated for different assumptions). Above 240 K,... 

Nuclear Magnetic Resonance (NMR) the Second Moment of the Line shape and Nuclear Spin-Lattice Relaxation... 

Carbon-12, the most abundant isotope of carbon, does not possess spin (I = 0) it has both an even atomic number and an even atomic weight. The second principal isotope of carbon, however, does have fhe nuclear spin property (I = j). atom resonances are not easy to observe, due to a combination of two factors. First, the natural abundance of is low only 1.08% of all carbon atoms are Second, the magnetic moment fi of is low. For these two reasons, the resonances of are about 6000 times weaker than those of hydrogen. With special Fourier transform (FT) instrumental techniques, which are not discussed here, it is possible to observe nuclear magnetic resonance (carbon-13) spectra on samples that contain only the natural abundance of... 

Nuclear magnetic resonance spectroscopy is a highly sophisticated analytical technique that can also be used to measure polymer crystallinity. Figure 1-36 shows proton resonance line width, and the second moment shows the crystalline behavior as an area. 

Nuclear magnetic resonance (NMR), in particular, deuterium NMR, has proven to be a valuable technique for determining the nature of molecular organization in liquid crystals. The utility of the NMR technique derives from the fact that the relevant NMR interactions are entirely intramolecular, i.e. the dominant interaction is that between the nuclear quadrupole moment of the deuteron and the local electric-field gradient (EFG) at the deuterium nucleus. The EFG tensor is a traceless, axially symmetric, second-rank tensor with its principal component along the C—D bond. In a nematic fluid rapid anisotropic reorientation incompletely averages the quadrupolar interaction tensor q, resulting in a nonzero projection similar to the result in Eq. (5.6) ... 

The effect of the dipole-dipole interaction is to give the nuclear magnetic resonance a finite width and shape. If it were not for this interaction, the resonance would approximate a spike (delta-function) at the resonance frequency. However, the width and shape frequently depend on the temperature via the diffusive motion of the host atoms or ions in the lattice. At temperatures low enough that the effects of diffusion can be neglected, information about the crystal structure of the solid can be obtained through the second moment of the experimental lineshape by comparing it with the theoretical value based on the formula due to Van Vleck (1948). The second moment of the resonance is defined as... 

The parameters characterizing the nuclear magnetic resonance in a solid, in particular the linewidth, second moment, and the spin-spin and spin-lattice relaxation times, are strongly affected by molecular reorientations and atomic diffusive motions. Application of NMR methods to the study of hydrogen (and deuterium) diffusion in the non-magnetic rare-earth hydrides has been extensive. 

Local mode relaxation of isolated lignin and its model compounds have been detected by dynamic mechanical measurement, and broad-line nuclear magnetic resonance spectroscopy (b-NMR) [49,53], although this molecular motion has scarcely received attention in recent papers. Transition map of local mode relaxation of various kinds of polymers is found elsewhere [56]. Figure shows second moment of absorption line of b-NMR of DL in powder form. When the relaxation is from the... 

The second category of human capacity enhancement is augmentation. Augmentation is well exemplified with nuclear magnetic resonance instruments. There is no a-priori human ability to detect the resonance of nuclear magnetic moments to an external magnetic field. NMR equipment gives humans instrumental access to physical phenomena beyond our unaided capacities. 

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