Computational Study of the Dissociation Reactions of Secondary Ozonide

Abstract

This contribution presents a comprehensive computational study on the reactions of secondary ozonide (SOZ) with ammonia and water molecules. The mechanisms were studied in both a vacuum and the aqueous medium. All the molecular geometries were optimized using the B3LYP functional in conjunction with several basis sets. M06-2X, APFD, and ωB97XD functionals with the full basis set were also used. In addition, single-point energy calculations were performed with the G4MP2 and G3MP2 methods. Five different mechanistic pathways were studied for the reaction of SOZ with ammonia and water molecules. The most plausible mechanism for the reaction of SOZ with ammonia yields HC(O)OH, NH3, and HCHO as products, with ammonia herein acting as a mediator. This pathway is exothermic and exergonic, with an overall barrier height of only 157 kJ mol−1 using the G3MP2 method. All the reaction pathways between SOZ and water molecules are endothermic and endergonic reactions. The most likely reaction pathway for the reaction of SOZ with water involves a water dimer, in which the second water molecule acts as a mediator, with an overall barrier height of only 135 kJ mol−1 using the G3MP2 method. Solvent effects were found to incur a significant reduction in activation energies. When the second H2O molecule acts as a mediator in the reaction of SOZ with water, the barrier height of the rate-determining step state decreases significantly.

An Experimental and Master Equation Investigation of Kinetics of the CH2OO + RCN Reactions (R = H, CH3, C2H5) and Their Atmospheric Relevance

“…For secondary ozonides, the barrier energies of the bimolecular reactions with NH 3 , H 2 O, and (H 2 O) 2 are high enough to effectively rule these reactions out. 53 It may appear that finally OH radical reaction with the stabilized dioxazole is the main degradation mechanism. Peeters et al’s SAR suggests the rate coefficient k OH = 8.5 × 10 –11 cm 3 molecule –1 s –1 for an alkyl-substituted cyclopentene, 54 which is a sum of rate coefficients for both carbons partaking in the C=C bond.…”

“…However, we can make some (very) rough estimates by assuming that the stabilized dioxazole has a similar bimolecular reactivity to secondary ozonides. For secondary ozonides, the barrier energies of the bimolecular reactions with NH 3 , H 2 O, and (H 2 O) 2 are high enough to effectively rule these reactions out . It may appear that finally OH radical reaction with the stabilized dioxazole is the main degradation mechanism.…”

Stability of Terpenoid-Derived Secondary Ozonides in Aqueous Organic Media

“… 12 Theoretical calculations have predicted that the reactions between C 2 SOZ and water molecules leading to the production of 2HCHO + H 2 O 2 are endothermic and endergonic. 13 Therefore, the fate of SOZs in the atmosphere should depend on their reaction with OH radicals or their uptake into atmospheric condensed phases such as aerosol particles, fogs, and cloud droplets. The latter process is expected to occur especially for large, functionalized, and hence low-volatility terpenoid-derived SOZs.…”

“…For example, the SOZ derived from propene ozonolysis undergoes unimolecular decomposition with a rate coefficient ( k ) of approximately 4 × 10 –8 s –1 at 295 K in the gas phase . Theoretical calculations have predicted that the reactions between C 2 SOZ and water molecules leading to the production of 2HCHO + H 2 O 2 are endothermic and endergonic . Therefore, the fate of SOZs in the atmosphere should depend on their reaction with OH radicals or their uptake into atmospheric condensed phases such as aerosol particles, fogs, and cloud droplets.…”

Computational Insights in DNA Methylation: Catalytic and Mechanistic Elucidations

“…On one side, it is well recognized that the occurrence of 5mC is mutagenic and can cause base mispairing G-T by the deamination of 5mC to thymine [5]. The deamination reactions of nucleic acid bases and related compounds have been extensively studied, the results of which are of great value in proposing the mechanisms investigated in this work [6][7][8][9][10][11][12][13]. On the other side, however, 3mC lesion affects the stability of single-strand (ss) and double-strand (ds) DNA [3].…”