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Structure determination examples

The frequency shifts caused by intramolecular H bonds furnish an aid to structure determination. Examples of compounds which are not included in the earlier discussion of dyes (Section 4.2.1) are given in Table 5-VIII. [Pg.184]

In nearly all derivatives, this ligand is di-anionic with both the aryloxide and carboxy-late oxygen atoms bound to the metal centre (Table 6.7). In one structurally determined example, the carboxylic acid group remains protonated and chelates to the metal... [Pg.501]

The preparation and structure determination of ferrocene marked the beginning of metallocene chemistry Metallocenes are organometallic compounds that bear cyclo pentadiemde ligands A large number are known even some m which uranium is the metal Metallocenes are not only stucturally interesting but many of them have useful applications as catalysts for industrial processes Zirconium based metallocenes for example are the most widely used catalysts for Ziegler-Natta polymerization of alkenes We 11 have more to say about them m Section 14 15... [Pg.610]

The compound anisatin is an example of a naturally occur ring 3 lactone Its isolation and structure determination were described in the journal Tetrahedron Letters (1982) p 5111... [Pg.815]

Another important area of analytical chemistry, which receives some attention in this text, is the development of new methods for characterizing physical and chemical properties. Determinations of chemical structure, equilibrium constants, particle size, and surface structure are examples of a characterization analysis. [Pg.9]

This electron microscopy reconstruction has since been extended to high resolution (3 A) where the connections between the helices and the bound retinal molecule are visible together with the seven helices (Figure 12.3c). The helices are tilted by about 20° with respect to the plane of the membrane. This is the first example of a high-resolution three-dimensional protein structure determination using electron microscopy. The structure has subsequently been confirmed by x-ray crystallographic studies to 2 A resolution. [Pg.227]

The structure of the reaction center also established that membrane-spanning helices can be tilted with respect to the plane of the membrane and that their relative positions within the membrane might be determined by the way they are anchored to the loop regions. Finally, several structures provide examples of how binding pockets for ligands are formed between such transmembrane-spanning helices. [Pg.248]

The situation is different for other examples—for example, the peptide hormone glucagon and a small peptide, metallothionein, which binds seven cadmium or zinc atoms. Here large discrepancies were found between the structures determined by x-ray diffraction and NMR methods. The differences in the case of glucagon can be attributed to genuine conformational variability under different experimental conditions, whereas the disagreement in the metallothionein case was later shown to be due to an incorrectly determined x-ray structure. A re-examination of the x-ray data of metallothionein gave a structure very similar to that determined by NMR. [Pg.391]

The formation of acyl halide-Lewis acid complexes have been observed by several methods. For example, both 1 1 and 1 2 complexes of acetyl chloride, with AICI3 can be observed by NMR spectroscopy. The existence of acylium ions has been demonstrated by X-ray diffraction studies on crystalline salts. For example, crystal structure determinations have been reported for /i-methylphenylacylium and acetylium ions as SbFg salts. There is also a good deal of evidence from NMR measurements which demonstrates that acylium ions can exist in nonnucleophilic solvents. " The positive charge on acylium ions is delocalized onto the oxygen atom. This delocalization is demonstrated in particular by the short O—C bond lengths in acylium ions, which imply a major contribution from the structure having a triple bond ... [Pg.584]

Among the variety of nitrogen-containing fulvalenes emerging from types 7-14, X-ray structural determinations have been performed on about 20 representative examples. Tire first crystal structure determination was carried out by application of the folding-molecule method on 3,3 -diphenyl-l,l -bi-isoindolylidene 64 (R = FI) (71CB3108). Tire dimeric isoindolenine system... [Pg.147]

An example of how information from fragmentation patterns can be used to solve structural problems is given in Worked Example 12.1. This example is a simple one, but the principles used are broadly applicable for organic structure determination by mass spectrometry. We ll see in the next section and in later chapters that specific functional groups, such as alcohols, ketones, aldehydes, and amines, show specific kinds of mass spectral fragmentations that can be interpreted to provide structural information. [Pg.413]

It is also possible to satisfy this relation and have the structure be underdetermined and locally over determined. Examples of two-dimensional structures are shown in Table 1. [Pg.51]


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See also in sourсe #XX -- [ Pg.40 , Pg.231 ]




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