DFT computational study of the epoxidation of olefins with dioxiranes

transition structures (TSs) of the reactions of dioxirane and dimethyldioxirane with ethylene, propene, cis-2-butene and trans-2-butene were located with the B3LYP/6-31G* method. The TSs of the reactions of ethylene and cis-2-butene exhibit a symmetrical spiro butterfly structure with synchronous formation of the two new C-O bonds and with substantial alignment of rr bond axis with the breaking O-O bond. In the case of propene and trans-2-butene a slight asynchrony in C--O bond formation was predicted by calculations. Theoretical activation free enthalpies (gas phase) reproduce the experimental (acetone solution) higher reactivity of cis with respect to trans disubstituted alkenes which in turn are correctly predicted more reactive than monosubstituted alkenes. Also the calculated absolute activation free enthalpies, after correction for electrostatic solvation effects by single point SCRF calculation (Tomasi model), were found to be in reasonable accord with experimental data. (C) 1998 Elsevier Science Ltd. All rights reserved.