Theoretical study on the comparative fate of the 1-butoxy and β-hydroxy-1-butoxy radicals

Theoretical high level ab initio BAC-MP4 and DFT calculations followed by a kinetic RRKM analysis have been performed in this work for the study of unimolecular reactions of the 1-butoxy and β-hydroxy-1-butoxy radicals. We have shown that the substitution of H by OH on the carbon in the β position of the 1-butoxy radical (leading to the β-hydroxy-1-butoxy radical) results in an important lowering of the decomposition barrier and a slight increase of the isomerisation barrier. Coupled to the rate constant calculations, this study suggests that, contrary to the fate of the 1-butoxy radical, the thermal decomposition is the major pathway for the β-hydroxy-1-butoxy radical. We have also shown that, under atmospheric conditions (760 Torr and 298 K), both isomerisation and decomposition processes are still in the fall-off range for the hydroxy radical. These behaviors have been interpreted in terms of electronic structures and intramolecular hydrogen bonding. This is the first theoretical study of the β-hydroxy-1-butoxy radical unimolecular reactions. As there are no experimental measurements on the β-hydroxy-1-butoxy radical rate constants, this theoretical study is the first to predict kinetic parameters for the decomposition and isomerisation reactions of this compound.