Aromaticity

The concept of 'Aromaticity' dates back to 1855, when chemist August Hofmann used the word to describe a set of benzene-like compounds that feature phenyl groups. As the name suggests, one common characteristic is that they often have distinctive odoursplugin-autotooltip__plain plugin-autotooltip_bigOdorousness of chemical compounds

"In studies of vision and audition, stimuli can be chosen to span the visible or audible spectrum; in olfaction, the axes and boundaries defining the analogous odorous space are unknown. As a result, the population of olfactory space is likewise unknown, and anecdotal estimates of 10,000 odorants have endured.".

Over time, it was realised - through x-ray diffraction tests - that the structure of benzene took the form of a ring of six atoms (see Benzene structureplugin-autotooltip__plain plugin-autotooltip_bigBenzene structure

The benzene molecule is composed of 6 carbon atoms joined in a ring with 1 hydrogen atom attached to each. Because it contains only carbon and hydrogen atoms, benzene is classed as a hydrocarbon.

Although the compound has been very extensively studied since its first isolation in 1825, its molecular dynamics - especially at temperatures below 77K when it becomes a solid - are extremely complex and the underlying atomic mechanics are for the most part still obscure.). Later, atomic theory gave (partial) detail to the possibilities of the electron-sharing which held the ring together.

In the last few decades however, theorists have realised that the 'aromaticity' concept is far more complicated than was initially thought.

To the extent that it could now be said that discussions about the entire field are currently in crisis - some experts have even called the concept 'non-existent' [source below].

Numerous computational tools for aromaticity analysis have been introduced and novel classes of molecules that exhibit aromatic (or antiaromatic) features have been explored experimentally. Hence, the aromaticity concept is broader and possibly fuzzier than ever.

Source : Chem. Sci., 2023, 14, 5542-5544

Some research groups are now suggesting that the concept can only be understood by calling on quantum superpostionplugin-autotooltip__plain plugin-autotooltip_bigQuantum entanglement

Quantun Entanglement was first predicted by Albert Einstein, Boris Podolsky, and Nathan Rosen in 1935.

It has now been (unequivocally) experimentally demonstrated with photons, neutrinos, electrons, and even molecules and crystals :

In 2019, it was announced that 'superposition' had been achieved in an organic compound with more than 2,000 atoms. (ref. ideas. The details of which, however, are yet to be agreed upon.

While both aromaticity and its counterpart, antiaromaticity, are associated with the delocalization of electrons between nonorthogonal atomic orbitals, they lack a universally accepted and comprehensive definition.

Source :arXiv:2307.00672