Circular dichroism vibrational

Molecular chirality is most often observed experimentally through its optical activity, which is the elfect on polarized light. The spectroscopic techniques for measuring optical activity are optical rotary dispersion (ORD), circular di-chroism (CD), and vibrational circular dichroism (VCD). 

UNFOLDED PEPTIDES AND PROTEINS STUDIED WITH INFRARED ABSORPTION AND VIBRATIONAL CIRCULAR DICHROISM SPECTRA... 

Danya Yang and Arvi Rauk, The A Priori Calculation of Vibrational Circular Dichroism Intensities. 

In addition to a review of the recent developments in the preparation of chiral amino compounds, developments concerning the interpretation of their ORD and CD in the visible and ultraviolet spectral regions will be reviewed, together with the emerging impact of vibrational (infrared) optical activity (VOA) observations, including vibrational circular dichroism (VCD) and Raman optical activity (ROA) measurements23, on important stereochemical problems concerning chiral amino compounds. 

FIGURE 13. Vibrational circular dichroism and transmission spectra of (/ )-(+)- and (S)-(—)-N,N-dimethyl-or-phenylethylamine [(R)-(+)- and (S)-(—)-153] in carbon tetrachloride. Reprinted with permission from Reference 140. Copyright (1976) American Chemical Society... 

FIGURE 14. Theoretically simulated and experimental vibrational circular dichroism (VCD) and infrared (IR) spectra of (2S,3S)-2,3-dimethylaziridine [(2S,3S)-159] carbon tetrachloride in the region 700-1600 cm-1. Reproduced from Reference 149 by permission of the National Research Council of Canada... 

Over the past decade two forms of vibrational optical activity have become established. One is called vibrational circular dichroism (VCD), the extension of electronic circular dichroism into the infrared vibrational region of the spec-tram. The first measurements of VCD were reported by George Holzwarth and co-workers at the University of Chicago in 1973 for crystals (3) and 1974 for neat liquids (4). In VCD one measures the small difference in the absorption of a sample for left versus right circularly polarized incident infrared radiation. The early stages of the development of VCD have been reviewed from several perspectives (5-8). 

Vibrational circular dichroism arises from the interference of the electric dipole transition moment (p joi and the magnetic dipole transition moment (m )io and is proportional to the rotational strength, / ,o, where... 

Stephens, P. J. Claik R. Vibrational Circular Dichroism The Experimental Viewpoint, In Optical Activity and Chiral Discrimination Mason S. F., Ed. Reidel Dordrecht, 1979, pp. 263-287. 

For our purpose, it is convenient to classify the measurements according to the format of the data produced. Sensors provide scalar valued quantities of the bulk fluid i. e. density p(t), refractive index n(t), viscosity dielectric constant e(t) and speed of sound Vj(t). Spectrometers provide vector valued quantities of the bulk fluid. Good examples include absorption spectra A t) associated with (1) far-, mid- and near-infrared FIR, MIR, NIR, (2) ultraviolet and visible UV-VIS, (3) nuclear magnetic resonance NMR, (4) electron paramagnetic resonance EPR, (5) vibrational circular dichroism VCD and (6) electronic circular dichroism ECD. Vector valued quantities are also obtained from fluorescence I t) and the Raman effect /(t). Some spectrometers produce matrix valued quantities M(t) of the bulk fluid. Here 2D-NMR spectra, 2D-EPR and 2D-flourescence spectra are noteworthy. A schematic representation of a very general experimental configuration is shown in Figure 4.1 where r is the recycle time for the system. 

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