X-ray crystallographic data

Although many sterols and bile acids were isolated in the nineteenth century, it was not until the twentieth century that the stmcture of the steroid nucleus was first elucidated (5). X-ray crystallographic data first suggested that the steroid nucleus was a thin, lath-shaped stmcture (6). This perhydro-l,2-cyclopentenophenanthrene ring system was eventually confirmed by the identification of the Diels hydrocarbon [549-88-2] (4) and by the total synthesis of equilenin [517-09-9] (5) (7). 

Cyclosporin A forms white prismatic crystals from acetone and is only slightly soluble in water and saturated hydrocarbons, but is very soluble in methanol, ethanol, acetone, and diethyl ether. Optical and nmr data on cyclosporins and x-ray crystallographic data on cyclosporin A and an io do derivative have been reviewed (273,275). 

Fig. 3. Computer projections of P-cyclodextfin inclusion complexes of (a) (R)-propranolol and (b) (3)-piopianolol from x-ray crystallographic data. Dotted lines represent potential hydrogen bonds (see text). The configurations shown represent the optimal orientation of each isomer on the basis of the highest...

The second problem concerns isomers of these various systems. As illustrated, 2d might be presumed to be planar. Unlike nitrogen, the inversion at phosphorus is very slow and there are, in fact, five possible isomers of it (three meso and two dl pairs). The interconversion of these isomers is reported in a subsequent paper by Davis, Hudson and Kyba along with x-ray crystallographic data on the structure of the so-called isomer B . 

In the absence of X-ray crystallographic data vibrational spectroscopy can. sometimes provide information concerning the mode of ligation, the position of the two n(SO) stretching modes in particular often providing a useful but not always reliable diagnostic " ... 

Accurate X-ray crystallographic data indicate that 5-hydrazino-3-mercapto-1,2,4-triazole exists in the solid state as a betaine, either as 165 or 166, with strong inter molecular hydrogen bonding occurring be-... 

The secondary structure of DNA is shown in Figure B. This "double helix" model was first proposed in 1953 by James Watson and Francis Crick, who used the x-ray crystallographic data of Rosalind Franklin and Maurice Wilkins. Beyond that, they were intrigued by the results of analyses that showed that in DNA the ratio of adenine to thymine molecules is almost exactly 1 1, as is the ratio of cytosine to guanine ... 

As in the preceding case with molybdenum, the spectroscopic and X-ray crystallographic data suggest that the complexes obtained can be described as organometallic analogs of resonance-stabilized phosphonium ylides [74]. 

Measured by using Dreiding stereomodels. Remeasured distances (compare Ref. 166). X-Ray crystallographic data. ... 

Among the hexitols, n.m.r. and X-ray crystallographic data " showed that galactitol and D-mannitol exist as planar zigzag conformers. Solutions of the others contain appreciable proportions of sickle and other bent carbon-carbon chain conformers. The low sweetness of the hexitols could possibly be due to increased hydrogen-bonding due to increased chain-length. 

Structural aspects were discussed, but not heavily, in the first edition. The complexity of new compounds (and macromolecules) now being investigated has driven many of the technological advances in X-ray crystallographic data collection and structure solution over the last two decades. Small-molecule (m.w. < 1,000 g mol-1) structure determinations are now routinely carried out, and Co complexes constitute a significant proportion of these. Indeed, the incorporation of crystal structures in most papers reporting new synthetic coordination chemistry is now a standard feature much more so than at the time of CCC(1987) (Figure 1). Inevitably, most of the new compounds described herein have been the subject of crystal structure determinations, rather... 

X-ray crystallographic data for homoleptic [Ni°(L-L)2] diphosphine complexes with a NiP4 core are collected in Table 24. 

Twenty-two years later the isolation of the anti-pernicious anemia factor" was announced independently by Smith (5) and Riches (6). Seven years of chemical studies identified 5,6-dimethylbenzimidazole (7), D-ribose (5) and amino-propanol (9) as components of the anti-pemicious anemia factor", but the tetrapyrroline ring structure containing Co(III) awaited the X-ray crystallographic data on the cyano-derivative by Hodgkin and White (10—15). Once the structure of the antipemicious anemia factor was determined it was called Vitamin B12 (cyanocobal-amin). The recommendations of a number of commissions forms the basis of the present system of nomenclature for this molecule and these are presented in Fig. 1. 

Modified neglect of diatomic overlap (MNDO) calculations can support the structures assigned to certain of these fused tricyclic systems, such as 401, where confirmatory X-ray crystallographic data are lacking <1983JCM128>. 

X-ray crystallographic data has become available on the commercially important 1 1 copper complex azo dyes. The symmetrical dihydroxyazo ligand (16) forms the 1 1 square planar complex (17).13 A pyridine molecule occupies the fourth coordination site since this complex facilitated the formation of crystals suitable for X-ray diffraction. The complex (17) actually exists as an unusual trimer which is held together by long bridging interactions between the copper atom in one molecule and one of the hydroxy oxygen atoms from the adjacent molecules. 

There are two main caveats to Equation 9.4 firstly, that this formula gives SM in units of joule per kilogram per kelvin, meaning no account is taken of the volume of the material under test. For this, the density is required and these two parameters combine (-p ASM) to give a better characterization, with units of millijoule per cubic centimetre per kelvin, acknowledging the composition of the material in bulk. Densities can readily be calculated from X-ray crystallographic data so that this presents no extra hardship. Secondly, one should be aware that the highest possible spin is not always attained, and, particularly in 3d systems, it may be impossible to saturate the spin system in moderate fields [15]. 

X-Ray crystallographic data for several basic derivatives of H-1,2,3-triazole and benzotriazole are included in CHEC(1984) and CHEC-II(1996) <1984CHEC(5)669, 1996CHEC-II(4)1>. Hundreds of new 1 //-1,2,3-triazole structures have been analyzed since some crystallographic data for representative examples (structures 5-12) are collected in Table 1. 

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