Polymorphism of 4-bromobenzophenone.

A combination of single-crystal and powder X-ray diffractometry was used to study the structure of two polymorphs of 4-bromobenzophenone over the temperature range from 100 to 300 K. One of the polymorphs of the title compound was known previously and its structure has been determined at room temperature [Ebbinghaus et al. (1997).

New ortho-para conversion mechanism in dense solid hydrogen.

Analysis of recent measurements of striking changes in the rate of ortho-para conversion of solid H(2) up to 58 GPa shows that the conversion mechanism must differ from that at ambient pressure. A new conversion mechanism is identified in which the emerging excitations are coupled to the converting molecules via electric quadrupole-quadrupole rather than nuclear spin-spin interactions. The latter only initiates conversion while the coupling enhancement associated with the new mechanism is ensured by high compression and a gap closing, with the conversion energy diminishing strongly with increasing pressure.

Investigation of the structural phase transitions near 190 K in 4,4'-dichlorobenzophenone.

X-ray structure studies have been carried out on single crystals of 4,4'-dichlorobenzophenone at temperatures from 164 to 295 K. The structure determined at 164 K is monoclinic I2/c. Crystal data: T = 164 K; a = 24.