British scientists synthesized a record-high aromatic ring 162 with paired electrons of porphyrin 12 parts connected alkyne bridges. A study proving the feasibility of the rule hückel limiting law were for large molecules, published in the journal Nature Chemistry.
Aromatic molecules such as benzene, have a conjugated system of electrons located on the orbitals toroidal shape above and below the plane of the ring. The aromaticity of the molecule can be defined as the ability to cause the ring current under the action of external magnetic field. According to the hückel rule, if in the cyclic conjugation are [4n + 2] electrons in an external magnetic field the current in the ring will occur to weaken the influence of the field on the Central part of the aromatic molecules. If the number of multiples of four electrons, a molecule called antiaromatic, and in an external magnetic field increases its influence on the inner part of the ring. Rule reliably predicts the behavior of small molecules, which pair up to 22 electrons, but it is unclear whether there is a limit of aromaticity on the ring size, does this rule for larger macrocycles.
Michael Reckhaus (Michel Rickhaus) with colleagues from Oxford University have synthesized and tested the aromaticity of the porphyrin rings of links connected by alkyl bridges with up to 162 paired electrons. Chemists have used molecular spacers to maintain the annular shape of the molecule, like the spokes in a Bicycle wheel. Then, oxidizing the molecule to the desired number of electrons in the structure, the authors tested method spectroscopy nuclear magnetic resonance (NMR) implementation of rule of hückel limiting law were.