Single-crystal X-ray technique

These salts are soluble in diethyl ether and dichloromethane, but relatively insoluble in petroleum ether. The ethylzinc complex 55b was investigated by single crystal X-ray techniques, and the structure of the cation is shown in Figure 26. 

Interest in the monomerization of anthracene photodimers continues the head-to-tail dimer (290) (see p. 361) produced by irradiation of 9-cyanoanthracene has been investigated by two groups. " From results of differential scanning calorimetry and emission spectroscopy of cleaved surfaces of partially monomerized single crystals, it is suggested that the first exothermic peak (and the subsequent ones) arises from monomer crystallization in the photodimer host matrix. " Theocharis and Jones have also examined this retroprocess and using single crystal X-ray techniques they have shown that the first step in the solid-state thermal monomerization of this dimer is a... 

The crystal structures of JV-phenyl-3-(p-chlorophenyl)-2-propenimine (96) and N-methyl-W-phenyl-3-(p-chlorophenyl)-2-propenimmonium perchlorate (97) have been determined by single-crystal X-ray techniques. Both compounds exist as monoclinic crystals, space group P2Jc, with four molecules per unit cell The C-NMR spectrum... 

Although the positioning of metals differing by one atomic number is often difficult with single-crystal X-ray techniques, a difference of one electron between two sites... 

Two single crystals of phase II with different compositions were taken for this purpose. The crystal structure determination [2] was carried out using the single crystal X-ray technique. The main crystallographic and experimental information are given in Table 1. 

The formation of such materials may be monitored by several techniques. One of the most useful methods is and C-nmr spectroscopy where stable complexes in solution may give rise to characteristic shifts of signals relative to the uncomplexed species (43). Solution nmr spectroscopy has also been used to detect the presence of soHd inclusion compound (after dissolution) and to determine composition (host guest ratio) of the material. Infrared spectroscopy (126) and combustion analysis are further methods to study inclusion formation. For general screening purposes of soHd inclusion stmctures, the x-ray powder diffraction method is suitable (123). However, if detailed stmctures are requited, the single crystal x-ray diffraction method (127) has to be used. 

X-Ray Diffraction. Because of the rapid advancement of computer technology (qv), this technique has become almost routine and the stmctures of moderately complex molecules can be estabUshed sometimes in as Htde as 24 hours. An example illustrating the method is offered by Reference 24. The reaction of the acrylate (20) with phenyldiazo derivatives results in the formation of pyrazoline (21). The stereochemistry of the substituents and the conformation of the ring can only be estabUshed by single crystal x-ray diffraction. 

This chapter deals with single crystal x-ray diffraction as a tool to study marine natural product structures. A brief introduction to the technique is given, and the structure determination of PbTX-1 (brevetoxin A), the most potent of the neurotoxic shellfish poisons produced by Ptychodiscus brevis in the Gulf of Mexico, is presented as an example. The absolute configuration of the brevetoxins is established via the single crystal x-ray diffraction analysis of a chiral 1,2-dioxolane derivative of PbTX-2 (brevetoxin B). 

Single crystal x-ray diffraction is, without doubt, one of the most important techniques for the determination of molecular structures in the solid state. The technique is also pivotal to the determination of accurate bond lengths in molecules. However, the analysis of x-ray... 

Applications The general applications of XRD comprise routine phase identification, quantitative analysis, compositional studies of crystalline solid compounds, texture and residual stress analysis, high-and low-temperature studies, low-angle analysis, films, etc. Single-crystal X-ray diffraction has been used for detailed structural analysis of many pure polymer additives (antioxidants, flame retardants, plasticisers, fillers, pigments and dyes, etc.) and for conformational analysis. A variety of analytical techniques are used to identify and classify different crystal polymorphs, notably XRD, microscopy, DSC, FTIR and NIRS. A comprehensive review of the analytical techniques employed for the analysis of polymorphs has been compiled [324]. The Rietveld method has been used to model a mineral-filled PPS compound [325]. 

Among crystalline solids, typical second-order transitions are associated with abrupt intermolecular conformational, rotational, and vibrational changes and/or with abrupt changes in crystalline disorder and/or defects [7], These changes in crystalline solids are sometimes difficult to assign without the use of appropriate spectroscopic techniques such as solid-state NMR or a diffraction procedure such as single-crystal X-ray diffraction. 

With the rapid development of modem analysis techniques, especially the popularization of single-crystal X-ray diffraction equipment, the origin of various physical and chemical properties, and the clear elucidation of correlations between the structure and properties of Pcs have become possibilities. Together with the maturity and diversification of their modifications, many Pcs have been synthesized and their molecular structures characterized by X-ray diffraction analysis in the past 5 years [15-77]. 

Cucurbitine (47) is the active principle from the seeds of Cucurbita moschata Duch., which are used in Chinese folk medicine. The structure of this unique a-amino acid was established through a combination of chemical and spectroscopic techniques (81, 82). A single-crystal X-ray analysis of the perchlorate of cucurbitine has confirmed the original hypothesis and has established the absolute configuration of 47 (83). 

The main techniques employed for the characterization of clusters include UV/vis optical absorption, luminescence, mass spectrometry, X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and Fourier transform infrared (FT-IR). Single crystal X-ray diffraction (XRD) has been used to determine the structures of a few clusters [17-19]. 

In solution, multinuclear NMR spectroscopy is by far the most informative technique for analyzing the structure and bonding of phosphinocar-benes. In fact, prior to the synthesis and single crystal X-ray analysis of the (phosphino)(phosphonio)carbene 2d,28 the only spectroscopic evidence for the formation of carbenes came from NMR. 

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