W0054

Crystallography Without a Lattice. John L. Finney, Dept.of Physics and Astronomy, Univ. College London, Gower St., London WC1E 6BT, UK.

Molecular structure determination in crystals depends on the presence of the crystal lattice. In liquids, there is no such lattice, so phase relationships between scattered X-rays or neutrons are not preserved. Hence, only pair distance distributions can be obtained from simple diffraction experiments. Advances in the past thirty years in radiation sources, instrumentation, and computing have enabled us to go beyond this apparent limitation. We can now obtain detailed structural information on relatively complex liquids, and thus see clearly for the first time how molecules actually interact in solution, and how the solvent is perturbed by the presence of the solute. Using as an example recent work on aqueous solutions of tertiary butanol without and with added salt, the ways in which we can obtain high quality structural information in the absence of a lattice are summarised. Not only can we see how intermolecular interactions are influenced by changes in temperature and concentration; we can also begin to see how the salting out process operates and perhaps even glimpse a structural rationale for the Hofmeister series.