Rapid Hydrogen Shift Reactions in Acyl Peroxy Radicals

Area of Science:

• Atmospheric Chemistry
• Computational Chemistry
• Chemical Kinetics

Background:

• Acyl peroxy and hydroperoxy acyl peroxy radicals are key intermediates in atmospheric oxidation processes.
• Understanding their reaction pathways is crucial for accurate atmospheric modeling.

Purpose of the Study:

• To investigate the hydrogen shift (H-shift) reactions in acyl peroxy and hydroperoxy acyl peroxy radicals using quantum mechanical calculations.
• To determine the kinetics and equilibrium of H-shift reactions involving hydroperoxy groups (OOH).

Main Methods:

• High-level quantum mechanical calculations (CCSD(T)-F12a/cc-pVDZ-F12//M06-2X/aug-cc-pVTZ) were employed.
• Transition state theory with Eckart quantum tunnelling correction was used to estimate reaction rate constants.

Main Results:

• 1,X-OOH H-shift reactions in hydroperoxy acyl peroxy radicals are rapid ( > 10^3 s^-1) and reversible, favoring peroxy peroxoic acid formation.
• These H-shift reactions are significantly faster than reactions with NO and HO2 under typical atmospheric conditions.
• Fast H-shift reactions were also observed in pentane acyl peroxy radicals (C5-AOO).

Conclusions:

• The rapid 1,X-OOH H-shift reactions must be incorporated into atmospheric models for accurate oxidation of hydroperoxy acyl peroxy radicals.
• These findings highlight the importance of H-shift reactions in atmospheric chemistry and the potential formation of large acyl peroxy nitrate molecules.