Understanding Aromaticity in [5]Helicene-Bridged Cyclophanes: A Comprehensive Study

Area of Science:

• Organic Chemistry
• Computational Chemistry
• Physical Chemistry

Background:

• Cyclophanes and helicenes are complex organic molecules with unique structural and electronic properties.
• Aromaticity is a key concept in chemistry, influencing molecular stability and reactivity.
• Understanding π-electron delocalization is crucial for predicting aromatic behavior.

Purpose of the Study:

• To investigate the aromaticity of doubly and triply [5]helicene-bridged cyclophanes.
• To assess the extent of π-electron delocalization in these molecules.
• To determine if these compounds exhibit global ring currents indicative of π aromaticity.

Main Methods:

• Computational calculations of magnetic response.
• Calculation of electronic aromaticity indices.
• Analysis of π-electron delocalization pathways.

Main Results:

• Molecules exhibit local ring currents in the presence of an external magnetic field.
• Ring currents are diatropic in the six-membered rings and helicene arms.
• Discontinuous π delocalization at C-C single bonds prevents interconnected ring currents.
• Electronic indices indicate reduced electron delocalization in helicene arms compared to benzene.
• Magnetic and electronic criteria yield differing aromaticity assessments for helicene arms.

Conclusions:

• The studied helicene-bridged cyclophanes are not globally aromatic.
• Disrupted π-electron delocalization is the primary reason for the lack of global aromaticity.
• Magnetic and electronic approaches provide complementary insights into molecular aromaticity.