Aromatic rings rupture and their bonding becomes dynamic under strain Now in Nature Chemistry → Congrats team Chemistry at York #MolMatYork and Durham Chemistry, Promeet Saha Abhijit Mallick | PhD Aisha N. Bismillah 🍉 Andrew Turley Alyssa Avestro, PhD Video Dr Anna Tanczos

Aromaticity can be a powerful stabilising force. Pitting strain against aromaticity has given rise to many remarkable molecules (just a few shown below) We asked: What happens when the amount of strain in the system approaches or exceeds the aromatic stabilisation energy?

The aromatic ring we use is tropylium. Like benzene, it has 6π electrons. But, because of its larger size, it has slightly more conformational flexibility and roughly half of the aromatic stabilisation energy

Our calculations predicted that twisting the ring could favour a bicyclic (Dewar) structure

So we set out to make topyliums with incrementally more steric crowding around their periphery, combining rotor-like arrangements of Ph rings and π-extension of the tropylium. (see for some of our recent work on making these rotor-like systems)

Moderate overcrowding causes twisting, but the aromatic ring remains intact @PromeetSaha made this compound which has a 45° twist from the tip of the tropylium to the base of the naphthalene

But ramping up the strain further leads to a Dewar tropylium @Abhijit61891253 identified this rearrangement product by X-ray diffraction

NMR spectroscopy shows signals of the Dewar tropylium undergoing exchange and adding hydride traps some of the aromatic isomer So, surprisingly, the Dewar structure is in equilibrium with the aromatic isomer. Strain turns on a dynamic aromatic-to-nonaromatic equilibrium!

@NatureChemistry @ChemistryatYork @DurhamChemistry @PromeetSaha @Abhijit61891253 @ANBismillah @_AndrewTurley @ajavestro @SciCommStudios Incredible work and love the animation 😍 @PromeetSaha @mcgonigalgroup

@NatureChemistry @ChemistryatYork @DurhamChemistry @PromeetSaha @Abhijit61891253 @ANBismillah @_AndrewTurley @ajavestro @SciCommStudios Impressive! So much to learn here! Congrats Paul! and the team!

@NatureChemistry @ChemistryatYork @DurhamChemistry @PromeetSaha @Abhijit61891253 @ANBismillah @_AndrewTurley @ajavestro @SciCommStudios Very interesting work! congratulations Paul and the team!