Synthesis\nand Structure of Acetylenic Acylium Cations

Acetylenedicarbonyl\nfluoride and propiolyl fluoride were\ninvestigated\nin the Lewis acidic medium consisting of SbF<sub>5</sub>/CF<sub>3</sub>CH<sub>2</sub>F. The acetylenic acyl cations are characterized by\nvibrational spectroscopy, NMR spectroscopy, and single-crystal X-ray\ndiffraction. The protonated species of propiolyl fluoride decomposes\nin a few hours at −78 °C in a dynamic vacuum which leads\nto the formation of the corresponding acylium cation. The room-temperature\nstable methylated acyl fluoride was prepared in the ternary system\nCH<sub>3</sub>F/SbF<sub>5</sub>/SO<sub>2</sub>. The experimental data\nare discussed together with quantum chemical calculations on the M06-2X/aug-cc-pVTZ\nlevel of theory.