Structures of gas-phase C2F 7 (+) ions

Area of Science:

• Organic Chemistry
• Mass Spectrometry
• Computational Chemistry

Background:

• Perfluorinated organic compounds are valuable in materials science and pharmaceuticals.
• Understanding the isomeric structures and reactivity of perfluorinated ions is crucial for predicting their behavior.
• Previous studies on protio analogs suggest distinct benzyl and tropyl structures.

Purpose of the Study:

• To investigate the reactivity of C7F7+ cations derived from different perfluorinated precursors.
• To elucidate the structural assignment of reactive and non-reactive C7F7+ ions.
• To compare the relative stability of perfluorobenzyl and perfluorotropyl cations using computational methods.

Main Methods:

• Ion cyclotron resonance spectrometry was used to study ion reactivity.
• Reactions with hexamethyldisilazane were monitored.
• Collision-induced dissociation experiments were performed.
• AM1 and ab initio (3-21G, 6-31G*/MP2) calculations were employed to determine ion stability.

Main Results:

• C7F7+ from perfluorotoluene reacted with hexamethyldisilazane, while ions from perfluoronorbornadiene and perfluorobicyclo[3.2.O]hepta-2,6-diene did not.
• Collision-induced dissociation supported this reactivity difference.
• Computational studies indicated that the perfluorobenzyl ion is more stable than the perfluorotropyl ion, contrary to protio analogs.

Conclusions:

• The reactive C7F7+ ion is assigned the benzyl structure, and the non-reactive ion is assigned the tropyl structure.
• Computational results confirm the greater stability of the perfluorobenzyl cation.
• This study highlights the significant impact of fluorine substitution on ion stability and reactivity.