Crystal prevention

The needle-like shape of the crystals prevents their being easily poured (into the capsule) making them liable to felt so the aim is to produce short crystals either by a suitable selection of conditions for the reactions of diazotization and precipitation of the product (D. Smolenski and Plucinski [13]) or by the addition of certain substances to the solution from which the product is to be precipitated Garfield [14], for instance, suggests for this purpose the addition of triphenylmethane dyestuffs to the solution. 

Another conceivable structure, namely a monomeric four-membered ring, was observed when electron-withdrawing C6P5 substituents were introduced at boron to increase its Lewis acidity (compounds 40a-d).52 53 The presence of intramolecular P-B interaction was unambiguously substantiated by 31P and 11B NMR data (Figure 7). So far, the lack of suitable single crystals prevented structural characterization, but DFT calculations... 

Samples were provided by R. R. Chance then of Allied Corporation. The samples were used without further processing. Both the normal incidence specular reflection (15) and piezomodulated reflection experiments are described elsewhere (16). The size and physical character of the first three members of the phenylurethane series of PDA crystals prevented their investigation with our low temperature apparatus. 

In most cases, resveratrol oligomers have proven recalcitrant to crystallization preventing the widespread application of X-ray crystallographic techniques. Most resveratrol oligomers reportedly precipitate as amorphous off-white to reddish powders. This is likely the reason why there has only been one study published to date reporting the X-ray crystal structure of an O-methyl, dibromo-derivative of hopeaphenol (14b) [50]. 

Etidronate adsorbs to hydroxyapatite crystals, preventing both their growth and dissolution. 

The device can be used to replace the tuned circuit in an oscillator by providing the resonant frequency or it can be coupled to the oscillator circuit, which is tuned approximately to the crystal frequency. In this type, the crystal prevents frequency drift. The device is widely used in quartz clocks and watches. 

An alternative viewpoint as to the mechanism by which nucleating agents work renders the distinction between nucleating agents and film-formers less clear. The contention is that the chemicals act through adsorption on the salt crystals as they first form. The adsorbed film on each of the crystals prevents further crystal growth and the end result is that the system contains many millions of very minute crystals. 

Difficulties in obtaining large, high-quality cBN crystals prevent precise measurements of the properties of this material. Therefore, many properties of cBN are known with poor precision or even not known with any precision. Recent progress in computational physics has partly supplemented this information. Generally, various properties of crystals maybe calculated by using band theories, at least in the framework of one-electron theory (112). Experimental judgments are inevitable, however. 

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