Fumaryl chloride and fluoride were reacted with different Lewis acids to synthesize the intermediates of the Friedel‐Crafts acylation. The salt of the monoacyl cation [C4H2FO2]+[Sb3F16]− was obtained from the reaction of fumaryl fluoride with SbF5 in SO2ClF solutions. The reaction was repeated using fumaryl chloride as starting material, which reacted under halogen exchange to obtain the salt of the monoacyl cation [C4H2FO2]+[SbCl2F4]−. In addition, the reaction of fumaryl chloride with SbCl5 in SO2ClF was studied. The covalent donor‐acceptor complex C4H2Cl2O2 ⋅ 2 SbCl5 was formed, containing oxygen‐bonded Lewis acids. The compounds were characterized by low‐temperature vibrational spectroscopy. Single‐crystal X‐ray structure analyses were conducted for [C4H2FO2]+[Sb3F16]− as well as for C4H2Cl2O2 ⋅ 2 SbCl5. In the solid state of [C4H2FO2]+[Sb3F16]− C⋅⋅⋅O and C⋅⋅⋅F contacts are observed and the origin of these interactions is discussed by means of ESP maps and NBO analysis. The monoacyl cation is stabilized by electrostatic attraction and electron back‐donation from oxygen and fluorine ligands to the positive ring‐structured π‐hole at the oxocarbenium center. Besides, the formation of the diacyl cation is not observed, which is based on small distances between the positive charges involving charge‐charge repulsion. The great advantage of using fumaryl halides in Friedel‐Crafts acylation is featured by the possibility to synthesize ketones keeping an acyl fluoride moiety.

The Front Cover shows the monoacyl cation, which was formed from the reaction of fumaryl fluoride with the Lewis acid SbF5 in SO2ClF solutions. A little man, symbolizing SbF5, is taking away one fluoride ion from the monoacyl cation. A second little man, representing another SbF5, is approaching the remaining acyl fluoride group and wants to take the fluoride ion. However, the abstraction of the second fluoride, with formation of the diacyl cation, is not possible (based on charge‐charge repulsion). This is why a stop sign is placed in front of the acyl fluoride group. The trivial name of fumaryl fluoride originates from the plant fumaria officinalis, which is displayed in the background. We gratefully acknowledge the Botanische Staatssammlung München, in particular Siegfried Springer, for providing the picture of fumaria officinalis. More information can be found in the Research Article by A. J. Kornath and co‐workers.

Fumaramide was reacted with the superacidic systems XF/SbF 5 and XF/BF 3 (X = H, D) leading to the formation of the Odiprotonated species. Using an equimolar amount of the Lewis acids relating to fumaramide, a mixture of the diprotonated salt and the diadduct with O-coordinated HF was obtained. The salts D) were characterized by low-temperature vibrational spectroscopy. Single-crystal X-ray structure analyses were carried out for the compoundsand fumaramide. To discuss the experimental results, quantum chemical calculations were executed at the B3LYP/aug-cc-pVTZ level of theory. To investigate the impact of the protonation on the resonance + M effect and the electron distribution concerning the conjugated system ESP maps, NPA charges, and NBO analyses were consulted. Due to the protonation, the nitrogen lone pair contributes completely to the formation of the C=N πbond, stabilizing the C=N double bond character. Since no monoprotonation of fumaramide is observed, amide hydrolysis is possible simultaneously on both amide groups.