"This project aims to identify and exploit the properties of crystalline molecular materials that lead to single crystal to single crystal transformations (SCSCT). Chemical reactions involving bond formation and breaking generally do not proceed as SCSCT because of the significant structuralrearrangement involved in the process. There exists a small class of compounds for which this phenomenon is observed, however. The observation of a SCSCT implies a highly cooperative solid state transformation from one molecule to another and has fundamental ramificationsfor our understanding of crystal structure. Moreover the fact that a single crystal is produced allows easy characterization of the product by X-ray crystallography. This project will proceed in three stages:1. Design and react:This involve design, synthesis and characterization of compounds directed towards three goal reactions namely addition, substitution and condensation reactions. The Cambridge Structural Database (CSD) will be used to aid the design of target molecules for this reaction by carryingout searches for closely related crystal structures of chemically related compounds.2. Modification:Here, compounds identified as having successful single crystal to single crystal transformations (SCSCT) will be studied in more detail. Small structural modifications will be made to these compounds and their effects on the success of the SCSCT studied.3. Mechanistic studies:Insights will be gained by studying the nature of the SCSCT observed in 1 and 2. The exciting area of SCSCT will bring a new focus to solid state reactivity with the aim of developing a predicate similar to the topological postulate which is used frequently to determine the likely successof solid-state photochemical reactions, with a view to applying this to any molecule or reaction type and ultimately use this predicate to develop novel crystalline materials."