‘Dynamic bonds’ reshape the rules of aromaticity and chirality

New discoveries in ‘dynamic bonds’ could reshape our fundamental understanding of key chemical concepts, including aromaticity and chirality. A team at the University of York in the UK has synthesised a polycyclic molecule whose aromaticity can be switched on and off, as well as a carbon cage where chiral carbon atoms interconvert without breaking bonds at the stereocentre. This ‘subverts our view of carbon-based molecules as fixed objects’, according to lead author Paul McGonigal. In the future, these new concepts could one day underpin ‘new applications for dynamic molecular materials’.

The researchers started by studying fluxional molecules.¹ In these species, different functional groups interchange positions but, depending on the velocity of the process and the timescales of the observations, they may appear identical. An example is the extremely fast interconversion between cyclohexane chair conformations. In an attempt to control and condition the interconversion rates of a range of fluxional molecules, researchers at York started overcrowding the structures with bulky and highly crowded systems. ‘We were lucky to observe both phenomena while exploring the effects of bond strain in fluxional molecules,’ explains McGonigal. Previously, the team had used this strategy to create unusual luminescence in strained structures, such as molecular rotors. Now, the results demonstrate dynamism is more common in organic molecules than previously thought.