Reaction ofOHradical and ozone with methyl salicylate – aDFTstudy

Abstract

A theoretical study on the reaction mechanism of methyl salicylate (MeSA), a green leaf volatile organic compound with OH radical and ozone, has been carried out using density functional theory methods using B3LYP, M06-2X and MPW1K functionals with 6-311++G(d,p) basis set. The atmospheric degradation pathways of MeSA with OH radical are studied under two different pathways, viz. H-atom abstraction and electrophilic addition of OH radical. The hydrogen abstraction from -OH group is found to be the dominant reaction channel with small barrier height. Likewise, the electrophilic addition of OH radicals at the para position of MeSA is found to be favourable rather than the ortho and meta positions because of the small barrier height. However, the reaction of MeSA with respect to the addition of O 3 is initiated only through the cycloaddition to the C¼C bond, resulting in primary ozonide. The Arrhenius plot for most of the addition reaction shows positive temperature dependence, while for the abstraction reaction, it exhibits negative temperature dependence over the temperature range of 278-350 K. The calculated theoretical rate constants are in good agreement with available experimental data. Overall, the addition of both OH radical and ozone possesses ability to degrade MeSA, but slower when compared with the Cl radical.

First Experimental and Theoretical Kinetic Study of the Reaction of 4‐Hydroxy‐4‐methyl 2‐pentanone as a Function of Temperature

“…As shown in Table , this reaction channel is exothermic and exergonic with = –11.21 kcal mol –1 and = –13.85 kcal mol –1 at the B3LYP level of theory. From the earlier studies , it is well observed that early transition state exhibits exothermic nature of the reaction. Pathway 2: H‐atom abstraction from theCH 3 group in α position with respect to the carbonyl group . The H‐atom abstraction from the –CH 3 group in α position with respect to the carbonyl group proceeds through transition state TS2 to form a product complex (PC2).…”

“…As shown in Table III, this reaction channel is exothermic and exergonic with r H o 298 = -11.21 kcal mol -1 and r G o 298 = -13.85 kcal mol -1 at the B3LYP level of theory. From the earlier studies [37,38], it is well observed that early transition state exhibits exothermic nature of the reaction. 898Å.…”

Atmospheric Oxidation Reactions of Methyl Salicylate as Green Leaf Volatiles by OH Radical: Theoretical Kinetics and Mechanism

“…However, the 3 (C3) and 6 (C6) positions have individual VdW structure, shown as VdW2 and VdW4, respectively. Although Priya et al [20] . investigated the oxidation reaction of MeSa by OH radical previously at several levels of theory and reported the different barrier height for each level, but they did not report the formation of VdW complexes for the different positions of MeSa ring during the oxidation reaction.…”

“…As far as we know, the only theoretical study of the reaction of MeSa with atmospheric oxidants of OH and O 3 in the gas phase was performed by Priya et al [20] . who reported the para position as the most probable position with largest branching ratio due to its shallow potential.…”

A Theoretical Investigation of Gas Phase OH-Initiated Acenaphthylene Degradation Reaction

“…M06-2X/aug-cc-pVTZ level of theory was chosen for the stationary point geometry optimization and frequency calculations, which is believed that the extra exchange-correlation functional included for accurate thermochemical and kinetical calculations especially [24]. This method has been identified by a couple of relevant gas phase radical oxidation reactions [25] [26]. Furthermore, the intrinsic reaction coordinates (IRC) approach calculations were carried out at the same level in order to verify the designed transition structures connecting to the expected energy minima.…”