Double Hydrogen-Atom Exchange Reactions of HX (X = F, Cl, Br, I) with HO₂

Abstract

A novel double hydrogen atom exchange process, HX + H'O → H'X + HO for the halogen series X = F, Cl, Br, and I, is identified using theoretical methods. These concerted reactions are mediated through a stabilized five-membered planar ring transition state structure. The transition state barrier for the double exchange process is found to be significantly lower than that for the abstraction reaction of a single hydrogen atom. Density functional theory employing the M11 exchange functional is used to compute parameters of the potential energy surface and the rate coefficients are obtained using transition state theory with small curvature tunneling. For low temperatures, the exchange reaction proceeds at a rate several orders of magnitude faster than the abstraction channel, which is also calculated. The exchange process may be observed using isotope scrambling reactions; such reactions may contribute to observed isotope abundances in the atmosphere. The rate coefficients for the isotopically labeled reactions are computed. It is found that the trends in reactivity within the series of halogen reactions can be quantitatively understood using the degree of electron delocalization at the transition state. The barriers are found to fall as the electronegativity of the halogen atom decreases.

Weak Interactions in Interstellar Chemistry: How Do Open Shell Molecules Interact with Closed Shell Molecules?

“…The hydroperoxyl radical ( 2 A″ ground state) is a relatively newly detected species in the ISM, although it is an important and well-studied molecule on the atmosphere of Earth. There have also been some previous studies on the weak interactions of the peroxy radical with H 2 O, H 2 S, HCl, and HF (our results concur with these studies, vide infra ). − This molecule can indulge in weak interactions via any of the three atoms (H, O, and O) that it possesses and, therefore, presents a variety of possibilities. Its net spin density is shared between the two oxygens, with about 0.3 being the spin density on central oxygen and 0.7 being borne by terminal oxygen.…”

Reactions of Criegee Intermediates are Enhanced by Hydrogen‐Atom Relay Through Molecular Design

“…Examples include: (i) gas‐phase hydrolysis of HFCO is catalyzed by H 2 SO 4 ; (ii) decomposition of CF 3 OH is catalyzed by formic acid; (iii) SO 3 hydration is catalyzed by oxalic acid; (iv) SO 3 +NH 3 reaction is catalyzed by NH 3 , etc. Furthermore, double H‐atom exchange reactions of HO 2 +HX (X=F, Cl, Br, I) have also been predicted computationally …”

Kinetic Study of Gas-Phase Reactions of Pyruvic Acid with HO2

“…In previous works it had been discovered that HO 2 can catalyze intramolecular H atom transfer reactions through a concerted double H atom transfer mechanism. For reactions as simple as DX + HO 2 → HX + DO 2 (X = F, Cl, Br, I) , the process is operative. Karton studied the HO 2 catalyzed tautomerization of vinyl alcohol that operates via a similar mechanism.…”