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MCD of Non-aromatic Cyclic π-Electron Systems. Part 6: Pentalenes and Heptalenes

Fleischhauer, Jörg ; Raabe, Gerhard ; Klingensmith, Kenneth A. ; Höweler, Udo ; Chatterjee, Prabir K. ; Hafner, Klaus ; Vogel, Emanuel ; Michl, Josef (2022):
MCD of Non-aromatic Cyclic π-Electron Systems. Part 6: Pentalenes and Heptalenes. (Publisher's Version)
In: International Journal of Quantum Chemistry, 102 (5), pp. 925-939. Wiley, DOI: 10.26083/tuprints-00022457,

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Item Type: Article
Origin: Secondary publication service
Status: Publisher's Version
Title: MCD of Non-aromatic Cyclic π-Electron Systems. Part 6: Pentalenes and Heptalenes
Language: English

The magnetic circular dichroism (MCD) spectra of several stable derivatives of pentalene (1) and heptalene (2) have been recorded. The lowest energy transition (from the ground to the S state in perimeter model nomenclature) is extremely weak in MCD and in absorption. The sign patterns of the B terms for the first three strong transitions—N₁, N₂, P₁—in the order of increasing energy, are −−+ for 1 and ++− for 2. These findings are in perfect agreement with numerical results obtained at the SACCI level and with expectations based on the perimeter model of Parts 1–4 of this series, both of which lead to the conclusion that the magnetic mixing of the S excited state with the ground state is dominant. This is an extremely rare situation for an organic molecule, in which B term signs are normally determined by the mutual magnetic mixing of excited states. It can be expected to occur in other conjugated systems derived from 4N-electron perimeters that have a low-energy first excitation, which is of intrashell nature in the perimeter model and therefore is magnetic-dipole allowed. In contrast, all low-energy transitions in the much more common systems derived from (4N + 2)-electron perimeters are of intershell nature and are magnetic-dipole forbidden.

Journal or Publication Title: International Journal of Quantum Chemistry
Volume of the journal: 102
Issue Number: 5
Place of Publication: Darmstadt
Publisher: Wiley
Uncontrolled Keywords: magnetic circular dichroism; pentalene; heptalene; perimeter model
Classification DDC: 500 Naturwissenschaften und Mathematik > 540 Chemie
Divisions: 07 Department of Chemistry > Organ Chemistry
Date Deposited: 28 Nov 2022 09:11
Last Modified: 28 Nov 2022 09:12
DOI: 10.26083/tuprints-00022457
Corresponding Links:
URN: urn:nbn:de:tuda-tuprints-224575
URI: https://tuprints.ulb.tu-darmstadt.de/id/eprint/22457
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