Theoretical Study of an Authentic Hydrocarbon Ion Pair

Area of Science:

• Physical Chemistry
• Quantum Chemistry
• Organic Chemistry

Background:

• Historically, hydrocarbons were exclusively considered to contain covalent bonds.
• Okamoto et al. (1985) challenged this principle by demonstrating hydrocarbon salt formation.
• Quantum chemical calculations for these systems remain scarce.

Purpose of the Study:

• To investigate the existence and stability of hydrocarbon ion pairs in the gas phase.
• To explore the energetics of hydrocarbon ion pairs in various nonprotic solvents.
• To provide theoretical insights into the formation of stable hydrocarbon ion pairs.

Main Methods:

• Density Functional Theory (DFT) calculations.
• Complete Active Space Self-Consistent Field (CASSCF) calculations.
• Continuum solvation model (CPCM) for solvent energetics.

Main Results:

• Identification of a metastable, highly polar ion pair between tricyclopropylcyclopropenylium cation and a simplified Kuhn's anion.
• Calculated barriers to covalent structure formation range from 4.8 to 14.4 kcal/mol.
• Energy differences between ion pair and covalent forms range from 4.3 to 25.4 kcal/mol.

Conclusions:

• Hydrocarbon ion pairs can be kinetically and thermodynamically stable.
• Theoretical calculations support the existence of these non-covalent hydrocarbon structures.
• Strategy for stable ion pair formation involves using stable ions and increasing steric hindrance.