Reactions of organ crystals with gases.

Although reactions of molecular crystals are much more widespread than has been generally appreciated (53), the great sensitivity of their rates to seemingly trivial changes in molecular structure clearly provides a major stumbling block to the general utilization of such processes. A key to understanding the effects of structural changes has been provided by the demonstration of anisotropy of such reactions discussed in this article. It is recognized, however, that many factors in addition to those aspects of the crystal structure utilized in the discussion above may play a part in determining reactivity of crystalline solids with gases. The recent ready availability of crystal structure data for molecular crystals should lead to a more rapid development of the principles governing the packing of such crystals and their reactivity. The resulting control of such reactions should not only provide the means of causing them when they are desired, as, for example, for synthesis, but also the means of preventing them when they are to be avoided, as in the stabilization of pharmaceuticals. Finally, it appears that we have only just begun to exploit the potential reaction specificity and the exciting possibilities resulting from the unique symmetry properties of the crystalline state.