Vibrational Circular Dichroism Detects Symmetry Breaking due to Conformational Mobility in C-2-Symmetry Chiral Molecules and Provides Further Insight into Inter-Chromophoric Interactions

Year: 2020

Authors: Mazzeo G., Abbate S., Boiadjiev SE., Lightner DA., Longhi G.,

Autors Affiliation: Univ Brescia, Dipartimento Med Mol & Traslaz, Viale Europa 11, I-25123 Brescia, Italy; CNR, Ist Nazl Ott INO, Res Unit Brescia, Via Branze 45, I-25123 Brescia, Italy; Reg Hlth Inspectorate, 7 Prince Al Battenberg I Str, Pleven 5800, Bulgaria; Univ Nevada, Chem Dept, Reno, NV 89557 USA.

Abstract: Bicyclo[3.3.1]nonane-2,6-dione (1) and bicyclo[3.3.1]nona-3,7-diene-2,6-dione (2) have been examined by vibrational circular dichroism (VCD), which, as for most C-2-symmetric systems, exhibits strong VCD signals. In the case of 2, VCD signals are stronger and sharper with several bisignate doublets; for 1, signals are less intense and broader. The VCD and IR spectra are excellently predicted by DFT calculations: only one conformer is present for 2, while for 1, three main conformers, related through concerted skeleton torsional motions are present (two of them being interchanged by C-2-rotation). The VCD spectrum shows specific features for the different conformers, such that correct population factors are crucial for reproducing experimental data. Also, the TD-DFT prediction of ECD (electronic circular dichroism) spectra is good. By comparing the spectroscopic signature of the two molecules (both VCD and ECD) and by careful analysis of the theoretical results, the role of the C=C double bond in compound (2) is evidenced. The double bond contributes toward enhancing the CD response both electronically and vibrationally.

Journal/Review: Symmetry-Basel

Volume: 12 (11)      Pages from: 1752-1  to: 1752-13

More Information: Funding was provided by the Italian Ministry of Education, University and Research (MIUR) through the PRIN program (PRIN 2017, project “Physico-chemical Heuristic Approaches: Nanoscale Theory of Molecular Spectroscopy” (PHANTOMS), prot. 2017A4XRCA). We also thank Sebastian Cusumano for help with acquiring the VCD spectra.
KeyWords: vibrational circular dichroism (VCD); electronic circular dichroism (ECD); density functional theory calculations (DFT); bicyclic diones; C-2-symmetry
DOI: 10.3390/sym12111752

Citations: 2
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