Crystal forms closed

Conformation. Neutron diffraction studies of sucrose revealed the presence of two strong intramolecular hydrogen bonds 0-2—HO-1 and 0-5—HO-6 in the crystal form (7,8). These interactions hold the molecule in a weU-ordered and rigid conformation. The two rings are disposed at an angle close to 90°, with the glucopyranosyl and fmctofuranosyl residues adapting chair and T" twist conformations, respectively. 

CSD is bimodal with distribution spread closely around dominant size of seed crystals and broadly around crystals formed... 

The mica structure provides an interesting variation of the types of close-packing observed for large ions in crystals. The two central layers of 0 , OH-, and F- ions form close-packed planes with three spheres in a hexagonal unit of edge 5.2 A, at positions 00, l/i2/i, and VsVa relative... 

The main result of three papers respectively by Holland and Miller [91] and by Chau and Geil [96,97] is that the polymorph which results in crystallization at or close to r.t. of solutions of iPBl depends on the maximum temperature reached by the solutions (TMs), or, more precisely, on the temperature at which the solution has been equilibrated last, irrespective of the polymorph of the initial crystals. For example if samples of any of the three crystal forms are dissolved at concentrations of 0.01-0.03% in amyl acetate (clearing point 65 °C) and brought to Tms of 90 °C, kept there for 3 to 48 hours (ts) and then crystallized at temperatures (Tx) between 24 and 50 °C, then 100% form I crystals are obtained. With the same procedure but using a Tms of 120 °C, 100% of the chiral form III crystallizes. For shorter values... 

Knowledge of the structure, crystal form, reactions, etc., of the microcrystalline waxes must be worked out in as full detail as the paraffin waxes before we reach an understanding of the whole subject. In fact, the type of work recently reported by Mazee (69) would indicate that much can still be learned about paraffin wax, particularly through close study of pure paraffins and their mixtures. 

Half fill a fiask with a sat. aq. soln. of sodium carbonate, and boil the liquid for 15-20 minutes until a little monohydrated carbonate is formed. Close the flask with a cork, fitted with two glass tubes, and keep the temp, at 10°-15° till some crystals are formed. Rim in alcohol of sp. gr. 0 835 and temp, of 45° until the flask is full. Crystals of the a-salt are formed after standing four or five days at a temp, of 16 22°. The crystals are isolated, by drawing on the mother liquid, and adding alcohol before the mother liquor is quite gone. The remaining mother liquor is then drawn off. 

Forty parts of the decahydrated salt are boiled in a flask with 8 to 10 parts of water until everything is dissolved, and no monohydrated salt is formed. Close the flask with a cork fitted with two glass tubes. Pour in alcohol as in the preparation of the a-salt, and keep the fiask closed till the two liquids have mixed. Rectangular crystal-plates of the / -salt are formed—the growth of the crystals generally begins near the zone of contact of the two liquids. The crystals are left in contact with the alcohol six to eight days after the salt liquor has been drawn off. 

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