The results of B3LYP&PCM quantum-chemical calculations confirmed the possibility for formation of fluoro(heptafluorocyclohexa-1,3-dien-1-yl)xenon and (octafluorocyclohex-3-en-1-ylidene)xenon from (heptafluorocyclohexa-1,4-dien-1- yl)xenonium in liquid acetonitrile. The Xe(II) and C² atoms in the cation are characterized by a strong affinity for fluoride ion, but the Xe(II) atom binds acetonitrile molecule. The addition of F^- to C² in [XeC₆F₇]⁺ is more favorable (by 6 kcal/mol) than replacement of the fluorine atom on Xe(II) by MeCN molecule. The charge on the xenon atom in (octafluorocyclohex-3-en-1-ylidene)xenon is small, the Xe-C bond is weakened, and its cleavage leads to ring contraction to perfluoro(3-methylidenecyclopent-1-ene).