| Abstract
| - The strain energies (SE) for dioxirane (DO) dimethyldioxirane (DMDO) and related dioxiranes havebeen examined by several methods using high-level computational schemes (G2, G2(MP2), CBS-Q). A series of calculated O−O, C−O, and O−H bond dissociation energies (G2) point to specialproblems associated with classical homodesmotic reactions involving peroxides. The relative SEsof DO, DMDO, methyl(trifluoromethyl)dioxirane (TFDO), and difluorodioxirane (DFDO) have beenestimated by combination of the dioxirane with cyclopropane to form the corresponding 1,3-dioxacyclohexane. The relative SE predicted for DMDO (2) is 7 kcal/mol lower than that of DO,while the SE of 1,1-difluorodioxirane (4) is 8 kcal/mol higher. The most reactive dioxirane, methyl(trifluoromethyl)dioxirane (3), has an estimated SE just 1 kcal/mol greater than that of DO but 8kcal/mol greater than that of DMDO. Six independent methods support the proposed SE for DO of18 kcal/mol. The SE of the parent dioxirane (DO) has been estimated relative to six-memberedring reference compounds by dimerization of dioxirane and or its combination with cyclopropane.The relative SE of cyclic hydrocarbons, ethers and peroxides have been predicted by the insertion/extrusion of −CH2− and −O− fragments into their respective lower and next higher homologues.The moderated SE of DMDO (≈11 kcal/mol) has also been estimated on the basis of group equivalentreactions. The unusual thermodynamic stability of DMDO is largely a consequence of combinedgeminal dimethyl and dioxa substitution effects and its associated strong C−H bonds and C−CH3bonds. The data clearly demonstrate that the reference compounds used to estimate the SE forhighly substituted small ring cyclic compounds should reflect their molecular architecture havingthe same substitutents on carbon.
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