Electronic delocalization in charged macrocycles is associated with global aromaticity.

Area of Science:

• Organic Chemistry
• Supramolecular Chemistry
• Physical Chemistry

Background:

• Cycloparaphenylenes and porphyrin nanorings can exhibit macrocyclic ring currents upon oxidation.
• These ring currents have been used to classify molecules as aromatic or antiaromatic.
• The interpretation of ring currents for aromaticity assignment has been debated due to the lack of consistent correlation with electronic delocalization.

Purpose of the Study:

• To investigate the relationship between macrocyclic ring currents and electronic delocalization in oxidized cycloparaphenylenes and porphyrin nanorings.
• To provide a clearer criterion for assigning aromaticity or antiaromaticity in these macrocyclic systems.

Main Methods:

• Computational chemistry methods were employed to analyze the electronic structure of the molecules.
• Magnetic field effects and electron delocalization were studied in oxidized cycloparaphenylenes and porphyrin nanorings.

Main Results:

• The emergence of macrocyclic ring currents was found to be directly correlated with increased electronic delocalization.
• This correlation holds true for both cycloparaphenylenes and porphyrin nanorings.
• The study provides quantitative evidence linking observable ring currents to fundamental aromaticity criteria.

Conclusions:

• Macrocyclic ring currents in oxidized cycloparaphenylenes and porphyrin nanorings are reliable indicators of cyclic electronic delocalization.
• The findings support the assignment of these molecules as (anti)aromatic based on experimental and computational evidence.
• This work clarifies the controversial aspect of aromaticity assignment in macrocyclic systems.