Abstract
AbstractGas phase (298.15 K, 1 atm) enthalpies of formation (Δ~f~H°~(g)~), enthalpies of disproportionation to two corresponding acetylene molecules (Δ~rxn~H°~(g),Td→acet~), and enthalpies of isomerization from a tetrahedrane geometry to a 1,3-cyclobutadiene structure (Δ~isom~H°~(g),Td→CBD~) were calculated for the mono- through tetra-substituted hydro, fluoro, chloro, bromo, methyl, ethynyl, and cyano carbon tetrahedrane derivatives at the G4MP2 and G4 levels of theory. All derivatives have endothermic Δ~f~H°~(g)~ indicative of the cage strain in these systems. In all cases, Δ~rxn~H°~(g),Td→acet~ and Δ~isom~H°~(g),Td→CBD~ are predicted to be substantially exothermic. High quality linear regression fits within a homologous series were obtained between the number of substituents and the G4MP2/G4 estimated Δ~f~H°~(g)~. Via calculations on lower homolog members, this strategy was employed to allow extrapolated G4 and/or G4MP2 Δ~f~H°~(g)~ (as well as some Δ~rxn~H°~(g),Td→acet~ and Δ~isom~H°~(g),Td→CBD~) to be obtained for the mono- through tetra-substituted t-butyl, trifluoromethyl, and trimethylsilyl carbon tetrahedrane derivatives.
Highlights
Tetrahedrane (Figure 1) has long captured the imagination of theoreticians and experimentalists [1]
In concert, synthetic chemists are illustrating that the successful isolation of many tetrahedrane derivatives are likely within practical reach. 40 Our initial theoretical efforts focused on the mono- through tetra-substituted hydro, 41 fluoro, chloro, bromo, methyl, ethynyl, and cyano carbon tetrahedrane derivatives
A substantial number of prior theoretical works have estimated the ΔfH°(g) of the parent tetrahedrane at various levels of theory. This literature is summarized in our previous work [22], and our G4MP2/G4 ΔfH°(g) estimates for this compound are in excellent agreement with other high level calculations. 96 Tetrahedranes may disproportionate to two acetylenes, or may isomerize to a corresponding 1,397 cyclobutadiene
Summary
Tetrahedrane (Figure 1) has long captured the imagination of theoreticians and experimentalists [1]. 13 Abstract 14 15 Gas phase (298.15 K, 1 atm) enthalpies of formation (ΔfH°(g)), enthalpies of disproportionation to two corresponding acetylene molecules (ΔrxnH°(g),Td→acet), and enthalpies of isomerization from a tetrahedrane geometry to a 1,3-cyclobutadiene structure (ΔisomH°(g),Td→CBD) were calculated for the mono- through tetra-substituted hydro, fluoro, chloro, bromo, methyl, ethynyl, and cyano carbon tetrahedrane derivatives at the G4MP2 and G4 levels of theory.
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