Investigation of the Gas-Phase Reaction of Nopinone with OH Radicals: Experimental and Theoretical Study

Abstract

Monoterpenes are the most essential reactive biogenic volatile organic compounds. Their removal from the atmosphere leads to the formation of oxygenated compounds, such as nopinone (C9H14O), one of the most important first-generation β-pinene oxidation products that play a pivotal role in environmental and biological applications. In this study, experimental and theoretical rate coefficients were determined for the gas-phase reaction of nopinone with hydroxyl radicals (OH). The absolute rate coefficient was measured for the first time using a cryogenically cooled cell along with the pulsed laser photolysis–laser-induced fluorescence technique at 298 K and 7 Torr. The hydrogen abstraction pathways were found by using electronic structure calculations to determine the most favourable H-abstraction position. Pathway 5 (bridgehead position) was more favourable, with a small barrier height of −1.23 kcal/mol. The rate coefficients were calculated based on the canonical variational transition state theory with the small-curvature tunnelling method (CVT/SCT) as a function of temperature. The average experimental rate coefficient (1.74 × 10−11 cm3 molecule−1 s−1) was in good agreement with the theoretical value (2.2 × 10−11 cm3 molecule−1 s−1). Conclusively, the results of this study pave the way to understand the atmospheric chemistry of nopinone with OH radicals.

Mechanistic and kinetic study of limona ketone oxidation initiated by hydroxyl radical: impact of indoor air pollution

“…The kinetics for the H-atom abstraction sites were calculated at the M06-2X/6-311+G(d,p) level of theory for all the H-abstraction sites using the CVT/SCT method. Several previously reported theoretical studies 8,28,42,43 of atmospheric reactions showed that the M06-2X method gives more reliable kinetic results comparable with experimental studies. Therefore, herein, we have used the M06-2X method to calculate the rate coefficients.…”

“…The reaction energies obtained using the M06-2X, ωB97X-D, MP2 and CCSD(T) levels of theory are similar. As is well known from previous studies 8,22,27–29 M06-2X predicts accurate thermochemistry; herein, the discussions are based on the M06-2X method. The initial reaction of LK started from the reactant (R) to form the pre-reactive complex (RC) with an intermolecular hydrogen bond O25–H26⋯O10 in the form of a barrierless reaction.…”

“…Recent studies have investigated model emissions of VOCs, and clearly indicate that these kinds of terpenes are highly likely to play a role in the climate changes at the global scale and have provided possible feedback regarding greenhouse gas formation and CO 2 emissions. 8,9…”

“…Recent studies have investigated model emissions of VOCs, and clearly indicate that these kinds of terpenes are highly likely to play a role in the climate changes at the global scale and have provided possible feedback regarding greenhouse gas formation and CO 2 emissions. 8,9 Limonene (C 10 H 16 ), which is found in the essential oils of citrus fruits like oranges and limes, is one of the most abundant monoterpenes emitted in the atmosphere. It is widely used in various products, including cleaning agents, perfumes and even flavoring agents for food and beverages.…”

Mechanism and kinetics of atmospheric degradation of menthol initiated by hydroxyl radical

“…The majority of studies show that DFT is the most accurate and cost effective method for predicting thermodynamic and kinetic properties. 18,20,21 Due to the high computational cost, G3B3 22 calculation is performed only for the most favourable initial reaction. Each local minimum is confirmed with positive frequency whereas the transition state structures are identified solely with one imaginary frequency.…”