Solving the Puzzling Absolute Configuration Determination of a Flexible Molecule by Vibrational and Electronic Circular Dichroism Spectroscopies and DFT Calculations: The Case Study of a Chiral 2,2_-Dinitro-2,2_-biaziridine

摘要

The absolute configuration of a recently synthesized racemateof 2,2-dinitro-2,2-biaziridine (2a), a possible catalystfor asymmetric synthesis, has been determined by vibrationalcircular dichroism (VCD) spectroscopy in the mid-IR regionand DFT calculations. Electronic circular dichroism (ECD)spectra have been obtained and Time-Dependent DFT (TDDFT)calculations have been performed and found to be inagreement with the conclusions from VCD and DFT. A detailedconformational analysis, for approximately 300 geometries,has been carried out, allowing us to find evidence forthe most populated conformers chiefly contributing to VCDand ECD spectra. The proposed absolute configuration andprevalent conformers are in correspondence with an equalconfiguration of the nitrogen atoms of the two aziridine rings.