An example of anthropomorphic metaphor in exaplining science:
"Electron counting suggests COT [cyclooctatetraene] should be antiaromatic, but it escapes this fate by puckering up out of the plane, so that its π-orbitals no longer overlap and it becomes non-aromatic instead. Cyclobutadiene, too small to repeat the trick, sheds its antiaromaticity by instantly dimerising…
For Haley's aromatic-fused, TIPS-protected indacene-based molecules, the enhanced conductivity imparted by the narrow Homo-Lumo energy gap is only one aspect of its interesting electronic properties. 'These molecules want to escape the destabilising feature of antiaromaticity, so they readily accept electrons – like pentacene – but more unusually they also readily give up electrons,' Haley says. Accepting or donating electrons allows the molecule to escape its 4nπ-electron status – and enables the molecule to act either as a p-type or an n-type semiconductor. 'We've made molecules that behave as the active layer in an organic field effect transistor, so we now know this idea works,' Haley says…
In a light-driven reaction, the molecule becomes antiaromatic, then twists to escape the antiaromaticity – which favours the unusual cyclisation. 'By inducing transient antiaromaticity, we achieved this missing cycloaromatisation reaction,' Alabugin says…
In the team's second example, they accessed antiaromaticity by converting a polycyclic aromatic into a dianion in two steps. 'When we add the second negative charge by reducing one of the benzene rings, it adds as far as possible from the first negative charge,' Alabugin says. 'The molecule became anti-aromatic, but in a very localised way, directed by the location of the pre-existing negative charge.' The molecule escapes antiaromaticity at that hotspot by undergoing cyclisation, producing a molecule that is like a piece of graphene 10 rings in size – but where one of the cycles is a five-membered ring. 'By localising the antiaromaticity we could embed a five membered cycle into graphene, which would be something that's otherwise difficult to do,' Alabugin says….
Molecules that have formal antiaromatic character in the ground state – but remain stable because they escape antiaromaticity's effects by, for example, bending out of plane like cyclooctatetraene does – could be ideal starting points for developing singlet fission materials, Ottosson says."
Chemistry World
Dr Igor Alabugin, Department of Chemistry & Biochemistry, Florida State University; Dr Henrik Ottosson, Department of Chemistry, Uppsala University in Sweden; Prof. Michael Haley, Richard M. & Patricia H. Noyes Professor, Dept. of Chemistry and Biochemistry, University of Oregon, reported in:
Mitchell Crow, J. (2024). Illuminating antiaromaticity. Chemistry World, 21(5), 42-47. https://www.chemistryworld.com/features/illuminating-antiaromaticity/4019362.article
[Please be aware that a word may have different nuances, or even a different meaning, according to context.]« Back to Index
