Topological Ring-Currents and Clar Sextets in Fully Benzenoid Hydrocarbons. II. Large Structures Containing More than...

Area of Science:

• Theoretical Chemistry
• Computational Chemistry
• Organic Chemistry

Background:

• Previous studies calculated π-electron ring currents in benzenoid hydrocarbons using the Hückel-London-Pople-McWeeny (HLPM) method.
• It was observed that in smaller systems (<17 rings), full rings had higher currents than benzene, while empty rings had lower currents.

Purpose of the Study:

• To extend the investigation of π-electron ring currents to larger fully benzenoid hydrocarbons (up to 43 rings).
• To determine if the distinction between ring current intensities in full and empty rings holds for larger molecular systems.

Main Methods:

• Utilized the quasi-graph-theoretical, parameter-free Hückel-London-Pople-McWeeny (HLPM) method for calculations.
• Applied the method to a selection of fully benzenoid hydrocarbons containing up to 43 rings.

Main Results:

• All full rings in all studied structures exhibited ring currents greater than benzene.
• In larger systems, some empty rings showed ring currents exceeding the benzene value.
• In the largest structures, empty ring currents surpassed those in half of the symmetrically nonequivalent full rings.

Conclusions:

• Despite findings in larger systems, all full rings maintained currents greater than adjacent empty rings, indicating diatropic circulation.
• Strong diamagnetic circulation was observed around the perimeters of all studied systems.
• Topological HLPM results align qualitatively with ab initio calculations by Steiner et al.