Dative and Electron-Sharing Bonding in C₂ F₄.

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Chemical Physics

Background:

• Understanding the reaction mechanisms of small fluorinated molecules is crucial for predicting their chemical behavior.
• The dissociation of carbon-carbon double bonds is a fundamental process in organic chemistry with implications in various reactions.

Purpose of the Study:

• To elucidate the reaction pathway for the carbon-carbon double bond rupture in tetrafluoroethylene (C2F4).
• To investigate the electronic structure changes and bonding evolution during the dissociation process.
• To characterize the transition from excited to ground states of the resulting difluorocarbene (CF2) fragments.

Main Methods:

• Ab initio calculations using CASSCF(8,8)+NEVPT2 and CCSD(T) methods with aug-cc-pVTZ basis sets.
• Density functional theory (DFT) employing M06-L and M06-2X functionals with aug-cc-pVTZ basis sets.
• Analysis of bonding using Energy Decomposition Analysis-Natural Orbitals for Chemical Valence (EDA-NOCV).

Main Results:

• The C-C bond dissociation in C2F4 proceeds nonlinearly without an activation barrier.
• The process yields difluorocarbene (CF2) fragments in the 1A1 ground state.
• Bonding analysis shows a transition from electron-sharing (3B1 excited state) to dative bonding (1A1 ground state) as C-C distance increases.

Conclusions:

• The dissociation of C2F4 is a barrierless process leading to ground-state CF2 fragments.
• The electronic structure of CF2 undergoes a significant transformation during bond elongation.
• The nature of the C-C interaction evolves from sharing to dative bonding, reflecting the change in fragment electronic states.