The effects of self-aggregation on the vibrational circular dichroism and optical rotation measurements of glycidol

Abstract

The noncovalent interactions between glycidol molecules in the CDCl₃ solvent have been studied by means of vibrational absorption (VA), vibrational circular dichroism (VCD), optical rotation (OR) spectroscopy and density functional theory (DFT) calculations. The concentration dependence of the VA and VCD spectra and OR measurements at five excitation wavelengths, i.e. 589, 578, 546, 436 and 365 nm, has been reported. To model the effects of self-aggregation of glycidol on the measurements, the energetic and conformational properties of the glycidol monomer, dimer and trimer were evaluated and the corresponding VA, VCD and OR spectra were simulated. The results show that at 0.2 M or lower concentrations the self-aggregation of glycidol is negligible since the simulated VA and VCD spectra, with the contribution from only the monomeric glycidol conformers, reproduce well the features in the experimental spectra. At 3.5 M, the binary conformers dominate, while at the intermediate concentration of 1.1 M, both the monomeric and binary conformers are important. The comparison of the experimental and theoretical OR values supports the above conclusions. This work shows the potential of using multiple chiroptical spectroscopic methods in combination with theoretical calculations to probe the self-aggregation process of chiral molecules in solution. Such studies can in turn help to achieve reliably absolute configuration determinations in the cases when chiral molecules self-aggregate profusely.