The S_N2 mechanism (bimolecular nucleophilic substitution) involves rear-side attack of a nucleophile at a carbon atom, opposite to the leaving group being displaced. This one-step reactions proceed with inversion of stereocenters through a trigonal-bipyramidal penta-coordinated carbon atom. The animations show the degenerate S_N2 reaction of (R)-2-bromo-butane with bromide yielding (S)-2-bromo-butane (racemization).

Bromination of alkenes proceeds via the Ad_E2 mechanism (bimolecular electrophilic addition). First, cyclic bromonium ions are formed, which undergo ring opening through rear-side attack by bromide. The over-all process is a trans-addition of bromine. Starting from trans-2-butene, the (2R,3S)- and (2S,3R)-2,3-dibromo-butanes (erythro pair) are formed through initial front- and rear-side attack of the alkene, both compounds being identical, achiral meso-structures (homotopic carbon atoms in the bromonium ion). Contrary, the bromination of cis-2-butene yields the enantiomers (2R,3R)- and (2S,3S)-2,3-dibromo-butane (threo pair) as the racemate (enantiotopic carbon atoms in the bromonium ion). The animations display the stereochemical course of all reactions leading to any of the stereoisomeric products.

These animations display the calculated mechanism of the C-H-oxidation of methane through permanganate (the surfaces shown in these examples are not molecular orbitals, but simple test surfaces which I used for program development; if available, orbital data could have been used instead). Data provided by T. Strassner, TU München, Germany.

Lithiation of 5-methoxy- and 4-methoxy-1,2,3-triazine with lithium amide. The various models displayed differ by the mode with which the lithium cation is complexed in the transition states. Data provided by M. Urban, TU Darmstadt, Germany.

The animations display a proposed mechanism for the ion transport in perowskit type lattices. In this GaLaO₃ structure, the Lanthanum (green spheres), Gallium (yellow) and Oxygen (orange-red) ions migrate alternatingly from their original lattice positions to adjacent voids. In total, each cycle of four migration steps results in a configuration in which the voids are displaced by just one unit-cell, and the corresponding ions have moved in the opposite direction. Data provided by O. Schulz, TU Darmstadt, Germany.

The above scheme shows only the relevant atomic positions (La: shaded spheres, Ga: white, Oygen: black), the boxes correspond to lattice voids. Each cubic unit cell has dimensions 3.99 x 3.99 x 3.99 Å.

The animations below are simple examples of spinning structures like the solid-state geometry of a linked cyclodextrin derivative and a single molecule of pyrane.

In the center, the three-dimensional molecular electrostatic potenials for benzene and salicylic-acid are displayed for their rotating structures. The electrostatic potenials were rendered as transparent 3D contours with different color-scales (benzene: yellow for negative electrostatic potenials and blue for positive potenials; salicylic-acid: red-green-blue color scale for negative to positive potentials).

The rightmost animations display 'endless flights' through the three-dimensional lattices of inorganic structures such as diamond, graphite, and a zeolite (play these movies in loop-mode!).