The mechanism and kinetic aspects of the retro-ene reaction of the Allyl n-propyl sulfide and its deuterated derivative were studied using four different types of density functional theory methods with eight different levels of the basis sets. The activation energies were determined at 550.65 K. As a consequence of our calculations, a transition state is concluded that consists of a polar six-center cyclic structure. We found that the combination B3PW91/6-311CCG** produces activation energy values closer to the experimental ones, but the simpler combination B3LYP/6-31G* produces excellent values too in less time. Our calculations show that the activation parameters obtained from the B3 methods are better than those obtained using the BLYP method. The mechanistic studies on the reaction show that the reaction proceeds through an asynchronous concerted mechanism. Theoretical calculations indicate that the reaction displays a kinetic isotope effect of 2.86 at 550.65 K.

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