Aromaticity of the doubly charged [8]circulenes

Area of Science:

• Computational Chemistry
• Organic Chemistry
• Aromaticity Studies

Background:

• Tetraphenylenes, also known as [8]circulenes, are macrocyclic compounds whose aromatic character is of significant interest.
• Understanding current pathways is crucial for determining the electronic properties and aromaticity of these systems.

Purpose of the Study:

• To investigate the magnetically induced current densities and pathways in a series of fully annelated dicationic and dianionic tetraphenylenes ([8]circulenes).
• To assess the aromatic character of neutral and charged [8]circulenes using advanced computational methods.

Main Methods:

• Employed the Gauge Including Magnetically Induced Current (GIMIC) method to calculate current density susceptibilities.
• Analyzed calculated current density susceptibilities to deduce aromatic character and current pathways.

Main Results:

• Neutral [8]circulenes display two concentric pathways: an antiaromatic (paratropic) inner core and an aromatic (diatropic) outer rim, resulting in overall nonaromaticity.
• Dianionic [8]circulenes and certain dicationic species (e.g., those with CH-, SiH-) are aromatic, sustaining net diatropic ring currents.
• Other dicationic [8]circulenes (e.g., with O-, NH-) are strongly antiaromatic.
• GIMIC calculations provide more accurate aromaticity information than local indices like NICS and NMR chemical shifts.

Conclusions:

• The aromatic character of [8]circulenes is highly dependent on their charge state and substituents.
• The GIMIC method is a reliable tool for accurately characterizing the aromaticity of complex organic molecules.
• This study offers a deeper understanding of electronic delocalization in [8]circulenes.