Kinetic and mechanistic study of H radical capture reaction in inhibition chemistry of CF(3)CF(2)N = CFCF(3).

CONTEXT: This work delves into inhibition chemistry of CFCFN=CFCF triggered by H radical. Analyses of electrostatic potential on the van der Waals surface reveal that the -N=CF- double bond has two reactive sites for H addition, particularly at the C atom with low-energy antibonding orbitals, and both N and F atoms present strong electron-rich characters, as identified by global and local minima of negative electrostatic potential, respectively. Energetics and kinetics demonstrate that the reactants of CFCFN=CFCF + H prefer to undergo entrance additions rather than abstractions and substitutions. The addition to Mb1 dominates at low temperatures, the addition to Mb2 and the dissociation of Mb1 to Pb12 CFCFN=CHF + CF show fierce competition in leading role at moderate temperature zone, and then the dissociation of Mb2 to Pb16 CFC = NH + CF controls the overall mechanism at elevated temperatures. These four exothermic reactions release heat, which may enhance combustion, while two β-C-C scissions greatly contribute to inhibition by releasing CF and CF moieties. METHOD: High-level quantum chemical methods and transition-state theory-based kinetic simulations were employed in this study. The electrostatic potential on the van der Waals surface of CFCFN=CFCF was analyzed at the M06-2X/Def-TZVP level. Potential energy surfaces were characterized at the CCSD(T)/6-311+ +G(d,p) level based on B3LYP/6-311+ +G(d,p) optimized geometries. Kinetics and branching ratios for entrance additions and major consumption dissociations were predicted by solving RRKM/master-equations within 300-3000 K and 0.01-100 atm.