Biomedical subjects

Thomas Heine

Publications and source records attributed to Thomas Heine.

23 records · Page 2Linked to original sources

PubMed2004

Antiaromaticity in bare deltahedral silicon clusters satisfying Wade's and Hirsch's rules: an apparent correlation of antiaromaticity with high symmetry.

Entirely unlike the aromatic closo BnHn2- borane dianions, isoelectronic Si62- and Si122- are antiaromatic. Their Oh and Ih symmetries are responsible, as the other deltahedral silicon dianion clusters do not exhibit this behavior. These high symmetries prevent mixing among the degenerate lone pair and skeletal orbitals, leading to paratropic behavior.

Journal Article↗

PubMed2004

13C NMR fingerprint characterizes long time-scale structure of Sc3N@C80 endohedral fullerene.

(13)C NMR chemical shifts of Sc(3)N@C(80) were computed using quantum Born-Oppenheimer molecular dynamics simulations, followed by DFT-NMR calculations on a large series of snapshots. Whereas calculations of the C(3) static gas-phase optimized structure fail to reproduce the two-line experimental spectrum, long-time molecular dynamics simulations quantitatively reproduce the experiment.

Journal Article↗

PubMed2003

Do all-metal antiaromatic clusters exist?

As shown by detailed nucleus-independent chemical shift (NICS) analyses of the contributions of each molecular orbital, the very recently reported gas-phase all-metal Al4Li3- anion and its relatives (Kuznetsov, A.E.; Birch, K.A.; Boldyrev, A.I.; Li, X.; Zhai, A.I.; Wang, L.S. Science 2003, 300, 622) are aromatic rather than antiaromatic. The paratropic (antiaromatic) four-pi-electron contribution is overcome by the predominating diatropic effects of sigma aromaticity. However, true antiaromatic all-metal clusters, such as Sn62- (Schiemenz, B.; Huttner, G. Angew. Chem., Int. Ed. Engl. 1993, 32, 297), do exist.

Journal Article↗

PubMed2003

The change of aromaticity along a Diels-Alder reaction path.

[reaction: see text] Quinodimethanes are highly reactive toward dienophiles since Diels-Alder cycloaddition results in an aromatic product. Density functional-based (13)C, (1)H NMR, NICS, and MO-NICS calculations indicate that the increase of aromatic character of the developing benzenoid ring along the reaction path is especially pronounced after the transition state is reached, even though the number of pi orbitals decreases. The forming aliphatic ring exhibits large ring current effects during the reaction.

Journal Article↗

PubMed2003

Sigma-antiaromaticity in cyclobutane, cubane, and other molecules with saturated four-membered rings.

Dissected nucleus-independent chemical shift (NICS) analyses of cycloalkanes and cage hydrocarbons reveal contrasting ring current effects, diatropic in three- and five-membered and paratropic in four-membered ring systems. The large shielding effects of the C-C bonds of the archetypal sigma-aromatic, cyclopropane, are magnified in tetrahedrane and related structures. The remarkable deshielding effect of the cyclobutane C-C(sigma) bonds is general: cubane and cages with four-membered rings are strongly deshielding (i.e., sigma-antiaromatic).[structure--see text]

Journal Article↗