The structure, stability, and functionality of chemicals like drugs and plastics heavily rely on the chemical bonding within aromatic molecules.

Aromatic bonding is such a strong stabilizing factor that we tend to conceive of it as “a constant presence.” 

Yet, new research indicates that it may be “surprisingly dynamic.”

In a bid to challenge existing notions of chemical bonds, researchers from Durham University and the University of York have pushed molecules to their limits by twisting them beyond breaking point.

Specifically, they investigated the extent to which an aromatic ring’s chemical bonding can be twisted before its aromatic bonding ultimately gives way.

They accomplished this by creating dense aromatic rings. Instead of benzene, they chose tropylium, which has a ring of seven carbon atoms with shared electrons.

Because each of these carbon atoms may be functionalized, and the ring has seven attachment sites rather of benzene’s six, the researchers were able to jam more groups around the aromatic ring’s edge, putting additional pressure on it.

Researchers discovered that mild degrees of overcrowding caused the ring to twist without destroying its aromatic bonds.

By adding increasingly bigger groups around the ring’s edge, they further twisted the ring, causing the aromatic bonding to finally dissolve.

The seven carbon atoms are no longer surrounded by electrons, so the ring pinches in the middle to make two smaller flat rings.

Interestingly, the researchers discovered a balancing point at which the ring alternates between aromatic structure and two smaller rings. The pinched structure dominates the molecule’s lifecycle in this research, with just 10% of its time spent in the wider aromatic ring.

The findings of this work have been published in Nature Chemistry.

Commenting on the study’s outcomes, Dr. Paul McGonigal from the University of York stated: “In these overcrowded molecules, strain and aromatic bonding are delicately balanced. The structure, properties, and potential applications of a material are ultimately determined by this balance.

“The precise control over the twisting of our molecules is unprecedented.”

They “were not only able to twist an aromatic molecule up to the maximum amount of strain it can tolerate, but also to discover what happens when we push beyond that limit.”

The team hopes “this investigation is a step towards us being able to more routinely turn aromatic bonding ‘off’ and ‘on’ in a controlled manner.”

“The reversible pinching and reopening of an aromatic ring are truly remarkable,” remarks project lead investigator Promeet Saha.

“Aromatic bonding is such a powerful stabilising force that we usually think of it being a constant presence. However, our findings demonstrate that it can be surprisingly dynamic.”

Source: 10.1038/s41557-023-01149-6

Image Credit: Getty