Unraveling the\nAutoxidation Mechanisms of Limonene,\nα‑Pinene, and β‑Pinene: A Computational\nStudy with Reactivity Prediction Models

The hydrogen shift reactions of peroxy radicals derived\nfrom the\nȮH-initiated oxidation of three atmospherically important monoterpenes,\nlimonene, α-pinene, and β-pinene, have been studied. The\nBell–Evans–Polanyi relationship (BEPR), Marcus cross\nrelationship (MCR), and Robert–Steel relationship (RSR) are\nemployed to study the factors that contribute to the kinetics of the\nH-shift reactions. Our results show distinct kinetic behaviors based\non the size of the transition-state ring, the functional group present\nat the H atom abstraction site, and the type of carbon-centered radical\nformed. Except for the 1,5-H-shift reactions, the MCR successfully\npredicts the activation enthalpy with minimal mean absolute errors\nby dividing it into intrinsic and thermodynamic components. The RSR,\nwhich considers the bond dissociation energy, polarity effects, and\nstructure factor while calculating the activation enthalpy, exhibits\na good correlation (<i>R</i><sup>2</sup> = 0.97) with the\nactivation enthalpy calculated through electronic structure calculations.\nThe present study elucidates the factors contributing to the kinetics\nof the H-shift reactions, aiding in the development of reactivity\nprediction models.