Detalle de: Reaction Modes of Carbonyl Oxide, Dioxirane, and Methylenebis(oxy) with Ethylene: A New Reaction Mechanism

The reaction modes of the three isomers, carbonyl oxide ( A ), dioxirane ( B ), and methylenebis(oxy) ( C ), with ethylene ( E ) were investigated by using CASPT2, CCSD(T), and B3LYP with a 6-311+G(2d,2p) basis set. Contrary to general expectations, A prefers to react with E via a [4+2] cycloaddition reaction (activation enthalpy Δ H # (298) = 1.0 kcal/mol) to yield 1,2-dioxolane ( MA2 ) (reaction enthalpy, −65.0 kcal/mol) rather than via an epoxidation reaction (Δ H # (298) = 11.3 kcal/mol) leading to oxirane and formaldehyde. Epoxidation by B is slower in view of an activation enthalpy of 13.7 kcal/mol; however, it should proceed stereochemically similar as in the case of A . Biradicals C and E can undergo a pseudo-[4+2] cycloaddition reaction (Δ H # (298) = 1.8 kcal/mol), which leads to 1,3-dioxolane ( MC2 ) in a strongly exothermic reaction (Δ H R (298) = −84.5 kcal/mol). The results obtained lead to a mechanistic reconsideration of epoxidation reactions observed in the course of the ozonolysis. They also provide a general basis for comparing reactions of 1,3-dipolar compounds and 1,3-biradicals with unsaturated compounds.