Theoretical Insights into the Reactivity of M2CAA with OH Radicals and the Fate of Resulting Alkoxy Intermediates

ABSTRACT A comprehensive theoretical investigation was conducted to elucidate the mechanism, kinetics, and thermochemistry of the gas‐phase reactions between methyl 2‐chloroacetoacetate (CH 3 C(O)CHClC(O)OCH 3 , M2CAA) and hydroxyl (OH) radicals using the M06‐2X functional. The most thermodynamically stable conformer of M2CAA was identified at ambient temperature. Three primary hydrogen abstraction pathways were characterized, each proceeding through the formation of a prereactive complex, indicating that the reactions follow an indirect hydrogen abstraction mechanism. Rate coefficients for these pathways were calculated for the first time over a temperature range of 250–450 K using Canonical Transition State Theory (CTST). Based on these kinetic results, the atmospheric lifetime of M2CAA was estimated to be approximately 5.34 h. Furthermore, the atmospheric fate and primary degradation pathways of the resulting alkoxy radicals CH 3 COCHClCOOCH 2 O • and CH 3 C(O)C(O • )ClC(O)OCH 3 were also explored in detail for the first time.