Modelling reaction kinetics of distonic radical ions: a systematic investigation of phenyl-type radical addition to unsaturated hydrocarbons

Abstract

Gas phase ion−molecule reactions are central to chemical processes across many environments. A feature of many of these reactions is an inverse relationship between temperature and reaction rate arising from...

Gas-Phase Phenyl Radical + O2 Reacts via a Submerged Transition State

“…Hindered rotors are treated consistently across the Gorin model of the outer transition state, the PRC, the inner transition state, and the covalent phenylperoxyl complex, in which the internal degree of freedom of the OO rotation is predominantly conserved. Alternative treatments of this internal motion will therefore have little impact . However, the subsequent reactions of the phenylperoxyl complex will be sensitive to this treatment since the internal OO rotor and its associated entropy are significantly changed.…”

“…This method was detailed in a previous publication. 36 Briefly, a restricted Gorin model was used to model the barrierless entrance channel to the van der Waals complex, and the collision rate for phenyl + O 2 was calculated using long-range transition state theory. 37 Vibrations of the hypothetical transition state were modeled using a Morse potential to determine the moments of inertia for the restricted internal rotations.…”

“…Alternative treatments of this internal motion will therefore have little impact. 36 However, the subsequent reactions of the phenylperoxyl complex will be sensitive to this treatment since the internal OO rotor and its associated entropy are significantly changed. Predicted second-order rate coefficients for each reaction were determined by multiplying the collisional capture rate by the fraction of reactions that remain kinetically trapped in the covalent adduct product well.…”

Protonation Isomer Specific Ion–Molecule Radical Reactions

“…In the case of protonation, the site of protonation on a molecule influences photofragmentation distributions, photoisomerization rates, excited-state lifetimes, and spectroscopic profiles. − For radical ions, through-space charge effects have been shown to alter the reactivity of gas-phase reactions by several orders of magnitude. − Additionally, deprotonation can have unexpected consequences on radical reactivity. For example, HOMO-SOMO inversion for deprotonated anion radical ions drastically affects the stability of the radical site. , Techniques have been developed to generate radical ions with specific OEFs; − however, there is still much to discover about how OEFs influence the reactivity of radicals.…”

“…For ion–molecule distonic radical reactions, it is previously observed for 18 different reactions that the energy of the prereactive complex (PRC) has no correlation with the rate of the reaction. , Instead it is the stability of a long-range PRC transition state that primarily controls the reaction rate. This transition state energy has been used to predict the reactivity of similar distonic radicals, although this parameter is sensitive and requires careful calculation and benchmarking.…”