Similarity in Dissymmetry Factor Spectra: A Quantitative Measure of Comparison between Experimental and Predicted Vibrational Circular Dichroism

To quantitatively determine the agreement between experimental and calculated vibrational circular dichroism (VCD) spectra, a new approach, based on the similarity of dissymmetry factor spectra has been developed and implemented. This method, which places emphasis on robust regions both in the experimental and in the calculated spectra, has been tested with six chiral compounds of known absolute configurations, namely, (R)-(+)-3-chloro-1-butyne, (3R)-(+)-methylcyclopentanone, (3R)-(+)-methylcyclohexanone, (1S)-(-)-alpha-pinene, (1R)-(+)-camphor, and (S)-(+)-epichlorohydrin. The criterion of maximum overlap among experimental and calculated dissymmetry factor spectra is shown to have definite advantages over those using maximum overlap among VCD or absorption spectra individually. The new method provides a better assessment of the comparison between experimental observations and quantum chemical VCD predictions and improves the confidence in the assignment of absolute configurations.