Synchrotron-radiation X-ray diffraction studies of CaF2 at high pressures have been performed on a powder sample up to 45 GPa and on a single-crystal sample up to 9.4 GPa. The bulk modulus of the low-pressure phase was determined to be B o = 87 (5) GPa. A phase transition was observed at about 9.5 GPa. The transition is accompanied by a volume contraction of 11%. The high-pressure phase is orthorhombic PbC12 type (space group Pbnm). The sample only partially reverts to the low-pressure phase upon release of pressure.

The reductive coupling of ketones, induced by low-valent titanium, was studied by using benzophenone and cyclohexanone as model compounds. The reaction conditions were optimized. It is essential that TiCl3 is reduced completely before addition of the ketone. The reaction mechanism is deduced from ESR measurements. Both the inorganic and organic part of the radical reaction are discussed. Various techniques were invoked to obtain a model for the actual coupling site. The coupling reaction occurs on the surface of an active titanium specimen.In the early seventies three groups of investigators2"4 established that low-valent Ti, prepared by the action of

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