Conformational Analysis in Solution of a Chiral BisoxazolineMolecule: Vibrational Circular Dichroism Spectroscopy and DensityFunctional Theory Study

Abstract

The conformations of the chiral bisoxazoline: 2,2 -methylenebis[3a,8a-dihydro-8H-indeno[1,2-d]oxazole] (also named IndaBOX), have been studied. Density functional theory (DFT) calculations identify four inequivalent stable conformations. Two, I and II have, C 2 symmetry; two, III and IV, have C 1 symmetry. The electronic energies of I-IV are ordered: I < II < III < IV. The span in energy is <1.0 kcal/mole. Vibrational unpolarised absorption and circular dichroism spectra have been predicted for the four conformations using DFT. Comparison of population-weighted spectra to experimental spectra of CHCl 3 and CDCl 3 solutions in mid-IR region strongly supports the DFT predictions of the number, structures, and relative energies of the conformations of IndaBOX. This shows that DFT predicts spectra with a high degree of reliability. We will undoubtedly illustrate the advantage added by vibrational circular dichroism spectroscopy in conformational analysis and in the absolute configuration determination.

Determination of Absolute Configuration and Conformation of a Cyclic Dipeptide by NMR and Chiral Spectroscopic Methods

“…It is rather sensitive to the mutual orientation of distinct groups in the molecule, thus providing valuable three-dimensional structural information for determination of the absolute configuration. VCD and ROA have been widely applied to determine the ACs of chiral structures of small molecules, ,− as well as to structural studies of proteins, ,, viruses, , and drugs. , The two techniques have also been successfully used for the determination of the ACs of chiral molecules with multiple stereocenters, ,,− although cases have been reported in which, e.g., VCD has failed to resolve the configuration of all stereocenters …”