The structure and properties of monoprotonated propiolamide and diprotonated cellocidin

Abstract Propiolamide and cellocidin were investigated in superacidic media. In both acetylenic amides, the amide moiety is immediately monoprotonated in anhydrous HF, HF/SbF 5 and HF/BF 3 . An increase of SbF 5 does not lead to a more highly protonated species. The salts were characterized by low-temperature Raman, NMR and room temperature IR spectroscopy, as well as by single-crystal X-ray diffraction. The experimental data are discussed together with results of quantum-chemical calculations on the M06-2X/aug- cc -pVTZ level of theory, which are consistent with the observation of pure monoprotonation. The second protonation of the amide moiety or the triple bond is not observed due to the high positive charge caused by the monoprotonation.