Alternating behavior in furan-acetylene macrocycles reveals the size-dependency of Hückel’s rule in neutral molecules

Yuval Rahav, Shinaj K. Rajagopal, Or Dishi, Benny Bogoslavsky, Ori Gidron*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review


Aromaticity can be assigned by Hückel’s rule, which predicts that planar rings with delocalized (4n + 2) π-electrons are aromatic, whereas those with 4n π-electrons are antiaromatic. However, for neutral rings, the maximal value of “n” to which Hückel’s rule applies remains unknown. Large macrocycles exhibiting global ring current can serve as models for addressing this question, but the global ring current are often overshadowed in these molecules by the local ring current of the constituent units. Here, we present a series of furan-acetylene macrocycles, ranging from the pentamer to octamer, whose neutral states display alternating contributions from global aromatic and antiaromatic ring currents. We find that the odd-membered macrocycles display global aromatic characteristics, whereas the even-membered macrocycles display contributions from globally antiaromatic ring current. These factors are expressed electronically (oxidation potentials), optically (emission spectra), and magnetically (chemical shifts), and DFT calculations predict global ring current alternations up to 54 π-electrons.

Original languageAmerican English
Article number100
JournalCommunications Chemistry
Issue number1
StatePublished - Dec 2023

Bibliographical note

Funding Information:
This research was supported by the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation program (Grant Agreement No. 850836, ERC Starting Grant “PolyHelix”). This research was supported by The Israel Science Foundation – FIRST Program (grant No. 1453/19).

Publisher Copyright:
© 2023, The Author(s).


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