OO bond homolysis in hydrogen peroxide

Area of Science:

• Physical Chemistry
• Quantum Chemistry
• Computational Chemistry

Background:

• Hydrogen peroxide (H2O2) decomposition is crucial in various chemical and biological processes.
• Understanding the O-O bond homolysis mechanism is key to controlling H2O2 reactivity.

Purpose of the Study:

• To investigate the O-O bond homolysis in hydrogen peroxide using multiple high-level theoretical methods.
• To analyze the influence of basis set size on the calculated reaction energetics.
• To elucidate the role of hydrogen-bonded radical pair complexes in the homolysis pathway.

Main Methods:

• Hybrid Density Functional Theory (DFT) methods (B3LYP, M06-2X).
• Double-hybrid DFT (B2-PLYP).
• Coupled-cluster theory (CCSD(T)).
• Multiconfigurational methods (CASPT2).
• Systematic analysis of basis set effects.

Main Results:

• All employed theoretical methods indicate that O-O bond homolysis proceeds via hydrogen-bonded radical pair complexes.
• Reaction barriers for the collapse of these radical pairs back to H2O2 are negligible.
• The potential energy surface for the reaction is exceptionally flat.
• Hydrogen bonding energies within the radical pair complex are substantial, exceeding 10 kJ/mol across all methods.

Conclusions:

• The theoretical investigation provides a detailed mechanistic insight into H2O2 homolysis.
• Hydrogen-bonded radical pair complexes play a significant role, despite low reaction barriers.
• The findings highlight the importance of accurate theoretical modeling for understanding peroxide chemistry.