Related Experiment Videos
The four-electron diamagnetic ring current of porphycene
Erich Steiner1, Patrick W Fowler
1School of Chemistry, University of Exeter, Stocker Road, Exeter, UK EX4 4QD.
Organic & Biomolecular Chemistry
|August 21, 2003
Summary
Porphycene exhibits a unique pi ring current, driven by electrons in its HOMO levels. This electronic behavior explains observed NMR chemical shifts in this porphin isomer.
Area of Science:
- Quantum chemistry
- Organic chemistry
- Spectroscopy
Background:
- Porphycene is a structural isomer of porphin.
- Porphyrins are vital in biological systems.
- Understanding porphyricene's electronic properties is key to its potential applications.
Purpose of the Study:
- To investigate the electronic structure and aromaticity of porphyricene.
- To elucidate the origin of the pi ring current in porphyricene.
- To correlate calculated electronic properties with experimental NMR data.
Main Methods:
- Ab initio calculations using DFT B3LYP functional for geometry optimization.
- Calculation of current density maps with the ipsocentric coupled-Hartree-Fock CTOCD-DZ method.
- Determination of NMR shieldings using the CTOCD-PZ2 variant within the 6-31G** basis set.
Main Results:
- Porphycene displays a global diatropic pi ring current with bifurcation across its pyrrole units.
- The observed current is attributed to four electrons in near-degenerate HOMO levels.
- Calculated NMR shieldings align with experimental observations, including proton and nitrogen chemical shifts.
Conclusions:
- The electronic structure of porphyricene supports its aromatic character.
- The study provides a theoretical basis for interpreting porphyricene's spectroscopic properties.
- Porphycene's unique electronic features offer potential for novel chemical and biochemical applications.