The topology and the aromaticity of coumarins

Abstract

2H‐l‐benzopyran‐2‐one (coumarin), its isomers and derivatives are considered as aromatic or potentially aromatic chemical species and analyzed as such by use of standard and parameter‐varying graph‐theoretical procedures. Theoretical results are interpreted within the bounds set by existing chemical evidence.

Excited State Aromaticity and Antiaromaticity: Opportunities for Photophysical and Photochemical Rationalizations

“…Aihara also found stabilizing resonance energies for (4 n + 2)­π-electron annulenes with Möbius topology in their lowest excited states (e.g., Möbius benzene in the T 1 /S 1 states). Two years later Ilić, Sinković and Trinajstić reported topological resonance energies (TREs) for a large series of Hückel as well as Möbius annulenes in the ground states and lowest ππ* excited states . The same observation as that of Aihara was made, yet, it was also found that the TREs for large annulenes of both Hückel and Möbius topologies go to gradually smaller values (e.g., the TREs for CBD and [20]­annulene in their ππ* states are 0.304 and 0.080, respectively).…”

Response to Comment on Screening for PBT Chemicals among the “Existing” and “New” Chemicals of the EU

“…In organic chemistry, it is well-established knowledge that all of these rings are aromatic. Examples are cyanuric acid (both the enol and keto form), cytosine, coumarin (both rings), and pyrone and pyridone (see Figure ). In all these cases, the N and O atoms are sp2 hybridized and possess lone electron pairs in p orbitals that are available for delocalization.…”