Protonated Ethylene Carbonate: A Highly Resonance-Stabilized Cation

Area of Science:

• Inorganic Chemistry
• Physical Chemistry
• Computational Chemistry

Background:

• Ethylene carbonate is a widely used organic solvent and electrolyte component.
• Understanding its protonation behavior is crucial for applications in electrochemistry and catalysis.
• Superacid systems offer unique environments for studying reactive intermediates.

Purpose of the Study:

• To synthesize and characterize monoprotonated and diprotonated ethylene carbonate species.
• To investigate the electronic structure and bonding of the protonated ethylene carbonate cation.
• To compare experimental findings with theoretical quantum chemical calculations.

Main Methods:

• Reaction of ethylene carbonate with superacidic systems (HF/MF5, M=Sb, As).
• Characterization using low-temperature infrared and Raman spectroscopy.
• Single-crystal X-ray structure analysis of [C3H5O3]+[Sb2F11]-.
• Quantum chemical calculations (B3LYP/aug-cc-PVTZ).
• Natural Bond Orbital (NBO) analysis and 13C NMR spectroscopy.

Main Results:

• Successful synthesis of monoprotonated ethylene carbonate salts: [C3H5O3]+[SbF6]-, [C3H5O3]+[AsF6]-, and [C3H4DO3]+[AsF6]-.
• Attempted diprotonation resulted in the formation of [C3H5O3]+[Sb2F11]-.
• X-ray crystallography provided structural details of the [Sb2F11]- anion.
• NBO analysis indicated sp2 hybridization and a delocalized 6π-electron system in the [C3H5O3]+ cation.
• Experimental spectroscopic data (IR, Raman, 13C NMR) supported the computational findings.

Conclusions:

• The monoprotonated ethylene carbonate cation ([C3H5O3]+) exhibits significant electronic delocalization.
• The CO3 moiety within the cation possesses a stable 6π-electron system.
• Quantum chemical calculations effectively complement experimental spectroscopic and structural data for characterizing these species.