X-Ray crystal analysis

This is a simplified formula for tartar emetic, for X-ray crystal analysis and infrared studies indicate that the. Sb is a part of the antimonate anion [Sb(OH)4] and forms part of a cyclic system. 

The X-ray crystal analysis of 5-trimethylsilanyl-4-trimethylsilanylethynyl-l//-pyrazole-3-carboxylic acid ethyl ester was obtained only with / = 0.17 because the crystals of the molecule diffracted extremely weakly and only a very limited data set was available. This means that although the gross stereochemistry of the molecule has been determined, individual bond lengths are not reliable (88JOM247). 

In contrast to the other measurements, the X-ray crystal analysis of thieno[3,4-d]thiepin shows an azulene-like, planar structure.30... 

Since 2-pyridone (24a, Table 3) exists as an equilibrium mixture with 2-hydroxy-pyridine (25a)14), it is difficult to isolate 24a in a pure state. However, the complexation method using inclusion hosts is applicable for the isolation of keto-form 24a in a pure state. For example, 24a was isolated by inclusion complexation (1 2 complexes) with 1 (26a) (Table 3) and with 3 (27a) (mp 151-153 °C), respectively. Both 26a and 27a do not contain the enol form (25a). The structure of 26a was studied by X-ray crystal analysis (Figs. 7, 8)12>. Inclusion of the keto-form is understandable, because 1 and 3 form more stable hydrogen bonds with the carbonyl oxygen of the... 

To the resultant triethyl phosphonoformate (105 g, 0.5 mol) was added sodium hydroxide solution (250 ml, 10 M) over a period of 15 min at ambient temperature. The solution became hot, and ethanol by-product boiled off from the reaction mixture. Upon cooling, a precipitate formed, which was recrystallized from water to give colorless crystals of the pure trisodium phosphonoformate hexahydrate (27.5 g, 19%), which exhibited IR and NMR spectra and x-ray crystal analysis in accord with the proposed structure. 

Other than classical H and 13C NMR spectra which have been reported for these compounds, no detailed studies have appeared in the literature. One X-ray crystal analysis of the TBDMS-protected alcohol analog of acid 368 has been carried out for structural proof. 

X-ray crystal analysis indicates that the DABCO/CBiq complex consists of alternating planes of the diamine and carbon tetrabromide in which each acceptor is bound to two donor units. The quinuclidine/CBr4 complex consists of pairs of donor-acceptor systems in which every quinuclidine molecule is bound to only a single molecule of carbon tetrabromide. 

Johnson, C. K. (1965). X-Ray crystal analysis of the substrates of aconitase. V. Magnesium citrate decahydrate [Mg(H20)6][MgC6H507(H20)]2-2H20. Acta Crystallogr. 18, 1004-1018. 

Although the high resolution X-ray crystal analysis of 4,4 -bipyridine has not been reported, the crystal structure of 4,4 -bipyridinium chlorocuprate (22) has been discussed. Whereas the dimensions of the 4,4 -bipyridinium dication may have been distorted because of the influence of the bulky metal cation, it is interesting to note that the 4,4 -bipyridinium dication is planar with both pyridine rings lying in the same plane. In metal complexes of the parent 4,4 -bipyridine, however, the pyridine rings may be coplanar or rotated up to 40° with respect to one other. 

Pepinsky, R., 1952. Computing Methods and the Phase Problem in X-ray Crystal Analysis. Publ. by Pennsylvania State College, Pa., U.S.A. 

Addition Reactions. In general, polar molecules such as hydrogen halides add across the B—N bonds, the more electronegative group bonding to boron (91). The adducts are cydotriborazanes such as the product formed by reaction of B-trichloroborazine and hydrogen chloride (eq. 35). X-ray crystal analysis shows the structure exists in a chair conformation (124). 

Fig. 8-6.—A drawing showing the dimensions of the molecule of 4-amino-2,6-dichloropyrimidine as determined by x-ray crystal analysis.

Unlike 1,2,4- and 1,3,4-oxadiazoles, the 1,2,4-triazole heterocycle has the possibility of existing in different tautomeric forms (Scheme 20). X-ray crystal analysis of the peptide-based triazole 63 showed only one tautomerJ102 Additionally, the 13C NMR spectrum for this compound indicated only one tautomeric form since the signals due to C3 and C5 appeared as sharp peaks. This is not the case for some other peptidergic triazoles (Table 5) where peaks corresponding to C3 and C5 were broad and of low intensity or not visible. Differences in tautomeric preferences have been explained by the ability of some triazole-containing peptides to form intermolecular hydrogen bonds and thus stabilize one tautomer over the other. 

C4-position of the starting (3-lactam in diastereomeric ratios of about 85 15 (Scheme 4). Pure optically active compounds could be obtained in almost all cases after chromatography. Unambiguous structure elucidation could be achieved by X-ray crystal analysis and NOE investigations. 

Molecular and crystal structure of DAD are shown in Figure 3 and 4. DAD crystallize in a triclinic system with the non-centrosymmetric space group P1. The direction of polarization of DAD in the molecular crystal is perfectly aligned in one dimension as shown in Figure 4. X-ray crystal analysis of DAD also shows the existence of two hydrogen bonds between adjacent molecules, 0 1--H... 

Fig. 10. Conformation of the core trisaccharide of the AMype oligosaccharides a-D-Man-( 1 -3)-p-D-Man-(l-4)-P-D-Glc7VAc as obtained from the X-ray crystal analysis as space filling stereo plots. The reducing end is to the right...

Unfortunately, many of the structures that we have described have been determined using two-dimensional X-ray crystal analysis only. Although in favourable cases this method can be extremely powerful, and indeed until about ten years ago was almost the only practicable method, yet its accuracy and reliability are far below what can now be achieved by complete three-dimensional analysis. With the increasing availability of high-speed computational facilities and more accurate means of data collection, three-dimensional refinement of the more important structures could now be undertaken. A great field of interesting and important work therefore awaits the modern crystallographer, and we may soon expect results of an accuracy sufficient to provide critical tests of diverse theoretical treatments. 

The keto-enol equilibrium of the 1,3-diketones has been the subject of intensive studies using various physical techniques and theoretical calculations [78-80], Recently, X-ray crystal analysis of acetylacetone (83) was carried out at 110 K, and it was found that it exists as an equilibrium mixture of the two enol forms 83b and 83c [81]. Room-temperature studies show an acetylacetone molecule with the enolic H-atom centrally positioned, which can be attributed to the dynamically averaged structure 83d. Application of a crystal engineering technique showed that a 1 1 inclusion complex of83 can be formed with l,l/-binaphthyl-2,2/-dicarboxylic acid in which the enol form is stabilized by a notably short intramolecular hydrogen bond [82],... 

Oxidation of anopteryl alcohol with alkaline potassium ferricyanide yielded the carbinolamine ether (56 or 57) as a minor product (8%) and compound 58 as the major product. The structure of 58 was elucidated by an X-ray crystal analysis. Compound 58 was isolated from the oxidation reaction mixture only after acetylating the mixture, from which the carbinolamine ether was first removed, and then hydrolyzing the acetylated product. Acetylation of compound 58 gave triacetyl derivative 59, in which the epoxide ring was opened. 

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