Raman dual circular polarization,

Backscattered dual circular polarization results on ephedrine and its stereoisomers are reported by Yu et al. (1993). All four stereoisomers examined show very similar Raman spectra, but their ROA spectra nicely show the sensitivity of ROA to the configurations and conformations of the molecules. As the features observed seem to be connected to the local stereochemistry, it seems to be possible that in the near future, with some more experimental data at hand, to deduce the absolute configuration of molecules of unknown stereochemistry directly from the ROA spectra. 

The two most important experimental setups for the measurement of ROA are backscat-tering (180°) incident circular polarization (ICP) ROA and backscattering in-phase dual circular polarization (DCPi) ROA. The ROA and parent Raman intensities written in terms of ROA and Raman invariants in the FFR limit are given by... 

Yu G-S, Freedman TB and Nafie LA (1995) Dual circular polarization Raman optical activity of related terpene molecules comparison of backscattering DCP[ and right-angle ICP spectra. Journal of Raman Spectroscopy 26 733-743. 

Yu G-S, Nafie LA. Isolation of preresonance and out-of-phase dual circular polarization Raman optical activity. Chem. Phys. Lett. 1994 222(4) 403 10. 

VCD instruments, based also on the principles depicted in Figure 13, are in comparison to the ECD instruments, relatively new products on the market. Thus, there have been further developments. Two of them should be mentioned, namely, the use of the Fourier transform technology and the use of a second PEM with and without a second polarizing element. This dual polarization modulation (DPM) method increases the quality of the VCD spectra. Also, the Raman spectrometers for ROA, with which the difference of scattered left and right circularly polarized Raman light is measured, have been developed to a standard that allows systematic chiroptical analyses, nowadays. 

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