Intermolecular Hydrogen Transfer in Isobutane Hydrate

Abstract

Electron spin resonance (ESR) spectra of butyl radicals induced with γ-ray irradiation in the simple isobutane (2-methylpropane) hydrate (prepared with deuterated water) were investigated. Isothermal annealing results of the γ-ray-irradiated isobutane hydrate reveal that the isobutyl radical in a large cage withdraws a hydrogen atom from the isobutane molecule through shared hexagonal-faces of adjacent large cages. During this “hydrogen picking” process, the isobutyl radical is apparently transformed into a <em>tert</em>-butyl radical, while the sum of isobutyl and <em>tert</em>-butyl radicals remains constant. The apparent transformation from isobutyl to <em>tert</em>-butyl radicals is an irreversible first-order reaction and the activation energy was estimated to be 35 ± 3 kJ/mol, which was in agreement with the activation energy (39 ± 5 kJ/mol) of hydrogen picking in the γ-ray-irradiated propane hydrate with deuterated water.

Keywords

• hydrogen abstraction
• clathrate hydrate
• radical
• electron spin resonance
• activation energy