Showing papers on "Dodecahedrane published in 2010"
TL;DR: It is shown that first-principle calculations using a van der Waals density functional (vdW-DF) permit the determination of molecular crystal structure within density functional theory (DFT) and consequences for methods such as DFT-D are analyzed and DFT's transferability over the full range of separations is questioned.
Abstract: In this paper, we show that first-principle calculations using a van der Waals density functional (vdW-DF) [M. Dion, H. Rydberg, E. Schroumlder, D. C. Langreth, and B. I. Lundqvist, Phys. Rev. Lett. 92, 246401 (2004)] permit the determination of molecular crystal structure within density functional theory (DFT). We study the crystal structures of hexamine and the platonic hydrocarbons (cubane and dodecahedrane). The calculated lattice parameters and cohesion energy agree well with experiments. Further, we examine the asymptotic accounts of the van der Waals forces by comparing full vdW-DF with asymptotic atom-based pair potentials extracted from vdW-DF. The character of the binding differs in the two cases, with vdW-DF giving a significant enhancement at intermediate and relevant binding separations. We analyze consequences of this result for methods such as DFT-D and question DFT-D's transferability over the full range of separations.
28 citations
TL;DR: In this paper, first-principle calculations using a van der Waals density functional (vdW-DF), [Phys. Rev. Lett. $\mathbf{92}$, 246401 (2004)] permits determination of molecular crystal structure.
Abstract: In this paper, we show that first-principle calculations using a van der Waals density functional (vdW-DF), [Phys. Rev. Lett. $\mathbf{92}$, 246401 (2004)] permits determination of molecular crystal structure. We study the crystal structures of hexamine and the platonic hydrocarbons (cubane and dodecahedrane). The calculated lattice parameters and cohesion energy agree well with experiments. Further, we examine the asymptotic accounts of the van der Waals forces by comparing full vdW-DF with asymptotic atom-based pair potentials extracted from vdW-DF. The character of the binding differ in the two cases, with vdW-DF giving a significant enhancement at intermediate and relevant binding separations. We analyze consequences of this result for methods such as DFT-D, and question DFT-D's transferability over the full range of separations.
25 citations
TL;DR: In this article, through space NMR shieldings of dodecahedrane C20H20, of the isomeric hydrocarbons C 20H12, the ions C20 H122+ and C20 h122−, of fluxional fullerene C20 and of its dication C202+ have been calculated employing the NICS concept on basis of MP2/6-31G∗ geometries and visualized as iso-chemical-shielding/deshielding surfaces (ICSSs).
Abstract: The through space NMR shieldings (TSNMRS) of dodecahedrane C20H20, of the isomeric hydrocarbons C20H12, of the ions C20H122+ and C20H122−, of the fluxional fullerene C20 and of its dication C202+ have been ab initio calculated employing the NICS concept on basis of MP2/6-31G∗ geometries and visualized as iso-chemical-shielding/deshielding surfaces (ICSSs). TSNMRS values were employed to study the exohedral magnetic properties of the compounds studied. Hereby, the curved π-conjugation in the compounds studied could be quantified.
11 citations
TL;DR: Two variants of the "SN 2 route" from pagodanes (A, B) to functionalized dodecahedranes (D, F, E) and particularly dodECAhedradienes (E) offer considerable improvements in the number of operations and yields (e.g., for diester F from 55-65 to 70-75 to 85-91%) as discussed by the authors.
Abstract: Two variants of the "SN 2 route" from pagodanes (A, B) to functionalized dodecahedranes (D, F) and particularly dodecahedradienes (E) offer considerable improvements in the number of operations (from nine to five to three) and yields (e.g., for diester F from 55-65 to 70-75 to 85-91%). Key steps are the regio- and stereospecific introduction of four to six bromine substituents into dimethyl pagodane-4-syn,9-syn-dicarboxylate (1 b) and a highly complex (thirteen bond-breaking/bond-forming events in four participating structures). yet very convenient (one-pot operation) and extremely efficient (nearly quantitative) transformation of secopagodane to bissecododecahedradiene with complete stereocontrol in transannular CH2 functionalizations. The prohibitively low kinetic acidity of "caged" hydrogens has so far only been overcome with the recently reported P2 F reagent (Schwesinger). Further improvement of the overall economy of the pagodane → dodecahedrane scheme has been achieved by efficiently channeling a byproduct of the pagodane synthesis (ca. 10%) back into the SN 2 track.