The Isomerization of Methoxy Radical: Intramolecular Hydrogen Atom Transfer Mediated through Acid Catalysis

Abstract

The catalytic ability of water, formic acid, and sulfuric acid to facilitate the isomerization of the CH(3)O radical to CH(2)OH has been studied. It is shown that the activation energies for isomerization are 30.2, 25.7, 4.2, and 2.3 kcal mol(-1), respectively, when the reaction is carried out in isolation and with water, formic acid, or sulfuric acid as a catalyst. The formation of a doubly hydrogen bonded transition state is central to lowering the activation energy and facilitating the intramolecular hydrogen atom transfer that is required for isomerization. The changes in the rate constant for the CH(3)O-to-CH(2)OH isomerization with acid catalysis have also been calculated at 298 K. The largest enhancement in the rate, by over 12 orders of magnitude, is with sulfuric acid. The results of the present study demonstrate the feasibility of acid catalysis of a gas-phase radical isomerization reaction that would otherwise be forbidden.

Intramolecular addition of oxyradicals to benzene rings: A DFT study

“…Intramolecular hydrogen abstraction, while thermodynamically favourable, is hindered by a significant barrier of the order of 19 kcal mol -1 . The (electronic) barrier for the 1,2-hydrogen shift is calculated to be even higher than this, which is in-line with very recent results on the 1,2-hydrogen shift of the methoxy radical 25 . The barriers for addition of the oxy-radical to the ortho-and ipso-positions of the β-phenyl ring are calculated to be significantly smaller, with values of around 10-11 kcal mol -1 for 1a.…”

Formic Acid Catalyzed Gas‐Phase Reaction of H2O with SO3 and the Reverse Reaction: A Theoretical Study

“…Although some recent reports [28][29][30][31][32][33][34][35][36][37] have demonstrated that water or acid can greatly reduce the activation barrier for various reactions, this is the first study on formic acid catalyzed hydration of SO 3 in the gas phase. Our results also confirm that this process is competitive with the reaction of SO 3 with the water dimer responsible for the formation of sulfuric acid and provide deeper insight into dissociation of the ground state of sulfuric acid, previously considered to be forbidden.…”

Das Methylsulfonyloxyl‐Radikal, CH3SO3

“…Insbesondere das schwefelzentrierte Radikal CH 3 OSO 2 kann leicht in SO 2 und das atmosphärisch bedeutende CH 3 O-Radikal zerfallen. [22] Abbildung 3. Berechnete Potentialenergie-Hyperfläche für die Isomerisierung von CH 3 SO 3 auf CCSD(T)/6-311 ++G(2df,2pd)-und CBS-QB3-Niveau( in Klammern).…”