AN EXPERIMENTAL COMPARISON OF VIBRATIONAL CIRCULAR-DICHROISM AND RAMAN OPTICAL-ACTIVITY WITH 1-AMINO-2-PROPANOL AND 2-AMINO-1-PROPANOL AS MODEL COMPOUNDS

Mid-IR vibrational circular dichroism (VCD) and the corresponding Rama n optical activity (ROA) spectra of 1-amino-2-propanol and 2-amino-1-p ropanol in neat solution are compared to yield insight into the domina nt structural sensitivity of each technique. The ROA spectra for these isomeric compounds are quite similar while their VCD spectra are subs tantially different. The contrast between the results with these two t echniques can be empirically interpreted to imply that VCD is more sen sitive to the overall chirality of a molecule, conformation plus confi guration, while ROA is more dependent on the nature of the local envir onment, or the configuration, of the functional groups. This observati on would correlate with VCD having a significant dipolar coupling cont ribution that is highly dependent on conformation. This distinction be tween VCD and ROA sensitivities would be expected to be most appropria te for high dipole strength transitions in conformationally unconstrai ned, open-chain molecules. These observations directly reflect the con trast between current applications of VCD and ROA to biomolecular conf ormational analyses.