The homotropenylium cation: a system with a pinched π ring current

Area of Science:

• Organic Chemistry
• Computational Chemistry
• Quantum Chemistry

Background:

• The homotropenylium cation is central to understanding homoaromaticity.
• Investigating the electronic structure and aromaticity of non-classical carbocations is crucial.

Purpose of the Study:

• To determine the aromatic character of the homotropenylium cation.
• To analyze the electronic current flow in relation to its unique bridged structure.

Main Methods:

• Constrained geometry optimizations of the homotropenylium cation.
• Ab initio calculation and plotting of current-density maps using the ipsocentric approach.
• Decomposition of localized orbital contributions to analyze ring current.

Main Results:

• A global diatropic ring current was identified passing through the CH2-bridge gap.
• A transition from pπ-pπ overlap to pσ-pσ overlap was observed within the bridge.
• A distinctive pinched current topology was revealed, indicative of global current flow.

Conclusions:

• The homotropenylium cation displays a global diatropic ring current.
• This magnetic criterion confirms the aromaticity of the homotropenylium cation.
• The study provides insights into the nature of homoaromaticity and electronic current distribution in bridged systems.