Rex Dark

A method for the prediction of the crystal structure of ionic organic compounds—the crystal structures of o-toluidinium chloride and bromide and polymorphism of bicifadine hydrochloride

The crystal structures of o-toluidinium chloride (1), o-toluidinium bromide (2) and two polymorphs of bicifadine hydrochloride (3) have been determined. The polymorphs of 3 differ in their molecular conformation and in their mode of packing. Crystallisation studies and quantum mechanical calculations show that the more readily crystallisable polymorph grows from the thermodynamically most stable conformer. On heating, conversion to the second polymorph takes place just below the melting point. The crystal structures of 1, 2 and the first polymorph of 3 have been successfully predicted using a procedure that is suitable for simple ionic organics.

Predicting and understanding crystal morphology: the morphology of benzoic acid and the polymorphs of sulfathiazole

Crystals of benzoic acid grown from dichloromethane and acetonitrile are greatly extended along the b-axis. The enhanced growth is not related to hydrogen bonding as benzoic acid is respectively dimeric and monomeric in these solvents. A mechanism is suggested for enhanced growth in the π-stacking direction for flat π-stacking systems. Facilities have been added to the Oscail software package which provide attachment energy calculations, crystal surface analysis and crystal visualization. Crystal surface analysis can be used to find the π-stacking direction and to identify the density of available hydrogen bond donors and acceptors on crystal faces. Observed and calculated morphologies for crystals of sulfathiazole form 2 grown from ethanol are in good agreement. Differences in the observed and calculated shapes of sulfathiazole forms 1, 3, 4 and 5 are attributed to solvent effects which correlate with the density of available hydrogen bond acceptors on crystal faces.

Persistent characterizations of injectors in finite solvable groups

Abstract In response to a question of Doerk and Hawkes [Finite soluble groups, de Gruyter, 1992, p. 553], we shall obtain characterizations of the injectors of a finite solvable group (without recourse to the concept of a Fitting set), and we also answer in the negative a question in [Dark and Feldman, J. Group Theory 9: 2006, p. 785].

Characterization of injectors in finite soluble groups

Abstract The purpose of this note is to describe when a subgroup of a finite soluble group is an injector of that group, without directly using Fitting sets.

BRVCEL ― A computer program for cell reduction and bravais lattice determination

Abstract BRVCEL was originally developed for use with the Hilger and Watts Y290 diffractometer. The program is, however, quite general and in use with an Enraf-Nonius CAD4 and has been found to be more successful and more convenient than the standard Nonius software. The program computes the Niggli cell, performs least squares on the Niggli cell dimensions, transforms to the conventional Bravais lattice and performs least squares on the conventional cell. The program can run with defaults on all tolerances or these may be set by the operator.

Fischer subgroups, Fitting height, and pronormality

Several authors have studied the relationship betweeen Fischer

On hypercentral groups and artinian modules

-subgroups and

On Camina Groups of Prime Power Order

injectors of a finite soluble group. Fischer [6] proved that when

On 2-generator metabelian groups of prime-power exponent

is a special kind of Fitting set, now called a Fischer set of G, the Fischer

Injectors with a central socle in a finite solvable group

-subgroups and the