Figure 2.

a) Schematic diagram of the in situ setup for investigating mechanochemical reactions in a tandem approach based on synchrotron X-ray powder diffraction and Raman spectroscopy. b) Crystal structure of the final product p-nitrobenzylidenemalononitrile (3) along the b-axis. c) Time-resolved X-ray diffraction patterns recorded during the Knoevenagel condensation of p-nitrobenzaldehyde with malononitrile yielding 3. Three phases can be distinguished based on the XRPD data. During the first 36 minutes, the reflections of the reactant 1 are observed. Within a time-span of nine minutes, the product is formed, evident from two strong reflections at 2θ = 14.6° and 25.7°. d) Time-resolved Raman spectra measured simultaneously (Here, the Raman spectra are shown with a 5 min interval. The complete set of spectra is shown in Supporting Information File 1, Figure S1.) The progress of the reaction can be detected from the decreasing signal of the C=O stretching band of 1 at 1706 cm⁻¹ (green) and the increasing signal of the C=C stretching band at 1581 cm⁻¹ (blue). The band attributed to the C≡N stretching shifts from 2266 cm⁻¹ (yellow) in 2 to 2233 cm⁻¹ (red) in the product. The first Raman spectrum shows the contribution of the empty jar. e) Course of the reaction detected by XRPD and Raman spectroscopy.