Rotational strengths comparison

Figure 2.18 Comparison of B3PW91 /TZ2P rotational strengths for R- and S-12 to the experimental rotational strengths of (+)-/2.

This is evident in a comparison of the expression for the magnitudes of optical activity, the rotator strength J ,, which is for an electronic transition 0 — fc,... 

Figure 6 Comparison of B3LYP/cc-pVDZ and experimental rotational strengths for (+)-R-1. Rotational strengths are in 1CT44 esu2 cm2.

Figure 12 Comparison of calculated rotational strengths for S-2 to experimental rotational...

The comparison of the computed rotational strength or the corresponding CD spectra with experimentally determined CD spectra. 

Optical Rotation.—The c.d. spectrum of (—)-/raw-l,2-di-4-pyridyloxiran (26) has been determined and rotation strengths have been compared with calculated values. The configuration of (—)-(26) was shown as by comparison with (-f)-R-/rfl 5-stilbene oxide. 

IR, Raman, and VCD spectroscopy all excite the same vibrational fundamentals. The respective vibrational spectra are different because the mechanism by which light is absorbed is different in each case, the amount of absorption depending on changes in the dipole moment, the polarizability and the rotational strength, respectively. AH these quantities are amenable to computation, and modern ab initio theory can reliably predict the frequencies of a molecule s vibrational fundamentals as well as the intensity of the signal in IR, Raman, and VCD spectra. The latter in particular are greatly assisted by electronic structure calculations comparison of experimental and theoretical VCD spectra enable absolute molecular conformations to be determined. 

Figure 2 Comparison of calculated and experimental rotational strengths for (1R, 4R)-(+)-camphor. R values are in 10- esu cm. The straight line has a slope +1.

We turn now to the VCD spectrum. Each VCD band corresponds to an absorption band. The assignment of the experimental absorption spectrum can thus be transferred directly to the experimental VCD spectrum. Comparison of predicted and experimental VCD intensities, fundamental by fundamental, can then be carried out. As seen in Figure 1, the agreement is qualitatively excellent. Quantitative comparison of calculated and experimental rotational strengths, the latter obtained by Lorentzian analysis of the experimental VCD spectrum, is shown in Figure 2. 

Figure 9.4 Strength comparison of film samples obtained with extruder screw rotation of 60rpm (notation as in Table 9.1).

Figure 9.8 Mechanical strength comparison of film specimens (screw rotational speed SOrpm, notation as in Table 9.2).

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