WHY DIELS-ALDER REACTIONS ARE NON-CONCERTED PROCESSES

Two exhaustive topological analyses using the Electron Localisation Function (ELF) along the non-polar Diels-Alder reactions of 1,3-butadiene [J. Phys. Chem. A 107, 6014 (2003)] and cyclopentadiene [Org. Biomol. Chem. 8, 5495, (2010)] with ethylene established that the bonding changes along these reactions are non-concerted. Herein, the ELF bonding changes along the intramolecular Diels-Alder reaction of 1-(hex-5-enyl) cyclohexa-1,3-diene is analysed. The geometrical restrictions imposed by the tether break the synchronicity in the single bond formation in this non-polar reaction. The present ELF topological analysis along this intramolecular Diels-Alder reaction supports the earlier findings that established the non-concerted nature of Diels-Alder reactions.