Do Anti‐Bredt Natural Products Exist? Olefin Strain Energy as a Predictor of Isolability

Bredt’s rule holds a special place in the realm of physical organic chemistry, but its application to natural products chemistry—the field in which the rule was originally formulated—is not well defined. Herein, the use of olefin strain (OS) energy as a readily calculated predictor of the stability of natural products containing a bridgehead alkene is introduced. Schleyer first used OS energies to classify parent bridgehead alkenes into “isolable”, “observable”, and “unstable” classes. OS calculations on natural products, using contemporary forcefield methods, unequivocally predict all structurally verified bridgehead alkene natural products to be “isolable”. Thus, when one assigns the structure of a putative bridgehead alkene natural product, an OS in the “observable” or “unstable” ranges is a red flag for error.     

Die Welt wird flacher. Beitrag der Chemie zum flachen Fernseher

Shorter switching times, a higher resolution, larger – and ever more widely used: that is a quick summary of the success story of LC displays. The secret behind it: liquid crystalline chemicals which are high‐tech materials with highly advantageous properties which allow for low‐weight and flat LCDs exhibiting a low power consumption. LCDs have made modern communication mobile and visible. For many years Merck has been the market and technology leader in the area of liquid crystals, of their mixtures and applications.     

Reversing the Handedness of Self‐Assembled Porous Molecular Networks through the Number of Identical Chiral Centres

Scanning tunnelling microscope observations at the 1‐phenyloctane/graphite interface reveal how chiral structural information at the molecular level is transferred and expressed structurally at the 2D supramolecular level for a porous system. The chirality of self‐assembled molecular networks formed by chiral dehydrobenzo[12]annulene (cDBA) derivatives having three chiral chains and three achiral chains, alternatingly, is compared with those of cDBAs having six chiral chains reported previously. While for all cDBAs homochiral surfaces are formed, their handedness is not simply a reflection of the absolute configuration of the stereogenic centres. Both the number of stereogenic centres as well as the length of the achiral chains determine the supramolecular handedness, providing a deep insight into the supramolecular chirality induction mechanisms at play. Moreover, these cDBAs act to induce chirality in porous networks formed by achiral DBAs.