Lopsided Benzene Sets A New Polarity Record

Chemists have made a new set of hexasubstituted benzenes in which electron-withdrawing cyano groups on one side of the ring and electron-donating amino groups on the other combine to pull and push the molecule’s electron density in the same direction. These compounds are remarkable for being the most polar neutral molecules now known to exist (Angew. Chem. Int. Ed. 2016, DOI: 10.1002/anie.201508249). Organic molecules with large dipole moments are desirable for their ability to enhance the efficiency of polymer films in electronic devices such as lasers, microchips for smart cards, and solar cells. Multisubstituted benzenes have long been synthetic targets, but chemists have been limited in their ability to prepare them using standard electrophilic substitutions. A research team led by Klaus Müllen of the Max Planck Institute for Polymer Research has now devised a new synthesis of hexasubstituted benzenes and dialkyldihydrobenzimidazoles via a new dibromo intermediate they prepared. The most polar molecule, 5,6-diaminobenzene-1,2,3,4-tetracarbonitrile, has a dipole moment of 14.1 debye, which is better than many ionic compounds such as sodium chloride (9 debye) and the aliphatic molecule record-holder hexafluorocyclohexane (6.2 debye), yet is still much less than that achieved by photosynthetic supramolecular assemblies (100 to 150 debye).