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Source of Structural Information

Angular restraints are another important source of structural information. Several empirical relationships between scalar couplings and dihedral angles have been found during the last decades. The most important one is certainly the Karplus relation for -couplings. Another, relaxation-based angular restraint is the so-called CCR between two dipolar vectors or between a dipolar vector and a CSA tensor. [Pg.211]

The most direct source of structural information, the diffraction studies, provides strong evidence for predominantly tetrahedral ordering of a molecule and its nearest neighbors, both in amorphous solid and liquid H2O. Other, weaker but still direct, structural evidence comes from the ratio of separations of nearest neighbor and next nearest neighbor 00 pairs in liquid water, the ubiquity of tetrahedral ordering in the several crystalline ices, and the statistical geometry of simulated water. [Pg.179]

Abstract Gas-phase electron diffraction is a unique source of structural information on... [Pg.197]

Like most other approaches to structural analysis of proteins, however, DSC is most valuable when it is not the only source of structural information concerning a given protein. DSC can provide evidence concerning the number of domains, or "cooperative unfolding units" into which a protein is divided, the stabilities of the individual domains. [Pg.313]

The data on the photoexcited triplets are a potential source of structural information. Specifically, dimerization effects on zfs s and kinetics may be of aid in the characterization of special pair... [Pg.140]

Transition metal NMR spectroscopy is not only a valuable source of structural information, but metal chemical shifts may also permit predictions of the reactivity and possibly even catalytic activity of a complex.51 The key to such analyses is frequently the observation of correlations of metal chemical shifts... [Pg.87]

The cationic Jt-allyl complex is often isolable and has been the subject of considerable study. X-ray structures of the 7t-allyl complexes with chiral ligands have been a primary source of structural information from which the design and predictive model of chiral catalysts derive. Chiral-metal-olefin complexes, which constitute another important class of intermediates have also been isolated, albeit few in number [31]. These static studies have been complemented by a growing number of NMR studies taking advantage of modem heteronuclear correlation and NOE techniques, which offer opportunities to monitor solution structures of the catalytic species [32-34],... [Pg.595]

The use of molecular mechanics as an aid in the interpretation of spectroscopic data is outlined in more detail in Chapter 9. One of the most rapidly developing applications of molecular mechanics is the use of the structures to aid in the analysis of multidimensional NMR spectroscopy125,261. This is particularly pertinent to the study of metal-macromolecule interactions where the spectroscopic data often have too low an observation/variable ratio to allow an unequivocal determination of the structure. Therefore, an additional source of structural information is needed. To date, there have been a limited number of studies involving metal ions but this area is likely to become a very important application of structural information from molecular mechanics studies (see also Chapter 9). [Pg.66]

Still another type of spectroscopy was added to the chemist s bag of tricks in 1946. In principle, it is similar to electron spin resonance, but it, is based on the spins of atomic nuclei, rather than electron spin. Nuclear spin resonance (or, as it is more often called, nuclear magnetic resonance) developed phenomenally in the 1950 s, and today it is a versatile source of structural information. [Pg.430]

Another source of structural information is the electrochemical response of the analyte to chemical perturbations. Changes in solution conditions have been useful in classical studies of structure-activity relationships. Exploration of a variety of solutions will help define the best conditions for particular classification problems. [Pg.109]

Ethylene has no dipole moment and a center of symmetry and therefore the Raman spectrum is an important source of structural information. After the early work on the rotational (Dowling and Stoicheff, 1959) and rovibrational Raman spectrum (Feldman et ah, 1956) these spectra were thoroughly studied in a series of publications (Hills and Jones, 1975 Hills et ah, 1977 Foster et ah, 1977). Overtones and combination bands were measured in an intracavity Raman experiment by Knippers et ah (1985). The Q-branch of the U2 band was resolved by pulsed CARS spectroscopy in a molecular beam experiment (Byer et ah, 1981). [Pg.294]

Two-dimensional nuclear magnetic resonance (2D NMR) techniques are the richest sources of structural information. They allow Eq. (5) to be formally expressed as... [Pg.288]

In addition, the measurement of a dipolar coupling constant (and hence of intemuclear distance) provides a rich source of structural information in MAS solid-state NMR. [Pg.140]

Caron, G. and Ermondi, G. (2003) A comparison of calculated and experimental parameters as sources of structural information the case of lipophilicity-related descriptors. Mini Rev. Med. Chem., 3, 821-830. [Pg.1004]

Many of the structural figures in this book have been drawn using atomic coordinates determined from X-ray diffraction experiments (see the individual figure captions). Databases such as the Cambridge Crystallographic Data Centre are invaluable sources of structural information (see the reference by A.G. Orpen below). [Pg.147]

Structural Study by Nmr.21 Though X-ray crystallography is the most precise source of structural information on boranes, nuclear magnetic... [Pg.243]

Oxide catalysts also frequently contain paramagnetic species, either as the result of redox behavior under process conditions or because these have been added intentionally to modify catalyst properties. In general, the paramagnetic species cause strong resonance shifts, line-broadening effects, and wide spinning sideband patterns (211, which together complicate analysis and interpretation of the spectra considerably. However, such shift effects in turn reveal structural proximity and thus have been used in favorable cases as a source of structural information [221. [Pg.201]

It seems worthwhile to point out here that, prior to the development and widespread applications of modem spectroscopic techniques (ir and nmr spectroscopy, mass spectrometry), dipole moments represented one of the most important sources of structural information about organic molecules. Although the importance of dipole moments in stmctural chemistry has diminished, they are still very useful and represent a way of obtaining different types of valuable data. [Pg.234]


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