Structural and Energetics Studies of Tri- and Tetra-tert-butylmethane

Abstract

Applying the G3 and G3(MP2) models and using both the isodesmic and atomization schemes, the heats of formation (ΔHf) at 0 and 298 K are calculated for mono-tert-butylmethane (2,2-dimethylpropane or neopentane, abbreviated as mono-TBM), di-tert-butylmethane (di-TBM), tri-tert-butylmethane (tri-TBM), and tetra-tert-butylmethane (tetra-TBM). Upon examining the results, it is found that all of the calculated ΔHf298 values are well within ±10 kJ mol-1 of the available experimental data for the first three compounds. Hence, for tetra-TBM, a compound that has not yet been synthesized, the G3(MP2) results reported in this work should be reliable estimates. Moreover, we have found that the atomization scheme is slightly more suitable for the study of the smaller molecules, while the isodesmic scheme is more suitable for the larger molecules. Structurally, it is found that the equilibrium structures of mono-TBM, di-TBM, tri-TBM, and tetra-TBM have Td, C2, C1, and T symmetry, respectively. The energy-minimized structure of each TBM molecule is determined and all structural parameters are generally in good agreement with the available experimental data. Furthermore, it is found that the innermost C−C bond lengths increase along the series mono-TBM < di-TBM < tri-TBM < tetra-TBM, a trend that is expected from steric consideration.