Real-Time In Situ Observation of Chemical Reactions

The process of chemical reaction in a crystal can be observed by stepwise crystal structure analysis if the single-crystal integrity is preserved during the reaction. Such a reaction is called a `crystalline-state reaction' and the stepwise crystal structure analysis is termed `real-time in situ observation'. Five examples of real-time in situ observation of crystalline-state reactions are briefly described. The first example is the optical enrichment of a racemic crystal by irradiation with visible light. The second example is in situ observation of hydrogen-deuterium exchange by neutron diffraction. The third example is the direct observation of the two-step inversion of a bulky chiral group on exposure to visible light. The fourth example is the real-time observation of two-step isomerization from a 3-cyanopropyl group to a 1-cyanopropyl group by irradiation with visible light. The fifth example is the insertion reaction of an oxygen molecule into an overcrowded distibene compound. In all the examples, the reaction mechanisms are clarified by the real-time in situ observation, which is a powerful method to analyze the mechanism of chemical reactions.