Theoretical studies on the dehydration reaction of the allicin radical cation in the gas phase

Abstract

On the basis of density functional theory (DFT), an investigation has been conducted about the dehydration reaction mechanism of the allicin radical cation in the gas phase as well as that of the protonated allicin. According to DFT calculations, the former is easier to take place than the latter, which agrees with the experiments. In the allicin radical cation, the allylic hydrogen atom on C1′ (adjacent to the divalent sulfur atom) attacks oxygen to yield the intermediate M1, in which the radical addition then take place to form six-member-ring intermediates ( M5 or M5′). Finally, the hydrogen atom on C1 (adjacent to the S–O bond) attacks the hydroxyl group together with the dissociation of S–O bond to produce the dehydration product ( M7 or M7′). On the other hand, in the protonated allicin, although the allylic hydrogen atom on C1′ is prior to that on C1 to attack the hydroxyl group, the former reaction will not yield the intact dehydration product but several fragments.