Dichroism inversion

The infrared absorption bands of syndiotactic PVC are classified into three groups from their dichroic properties. When the film is fully stretched, most of the bands show dichroism as shown in Fig. 1 (draw ratio 7). When the film is only partly stretched, some of the bands show the dichroism different from that observed for the fully stretched film. Fig. 1 (draw ratio 2.5) gives the result. This dichroism inversion is observed for four bands [J]. 

Thus the absorption bands are classified into three groups. The bands at 1426,1333, 1102 and 638 cm belong to group 1, which shows the perpendicular dichroism only. The bands at 1354, 1254, 957 and 603 cm belong to group 2, which shows the dichroism inversion. The bands at 1379, 1229 and 833 cm belongs to group 3, which shows the parallel dichroism for the fully stretched... 

The IR dichroism inversion is detected only for some absorption bands of the same chemical origin (NH or CO groups). This effect was extensively studied in [35] for a great number of block copolymers. Our data prove an analogous pattern of the IR dichroism inversion. 

Azetidine, 7V-bromo-, 7, 240 Azetidine, AT-r-butyl- N NMR, 7, 11 Azetidine, AT-t-butyl-3-chloro-transannular nucleophilic attack, 7, 25 Azetidine, 3-chloro-isomerization, 7, 42 Azetidine, AT-chloro-, 7, 240 dehydrohalogenation, 7, 275 Azetidine, 7V-chloro-2-methyl-inversion, 7, 7 Azetidine, 3-halo-synthesis, 7, 246 Azetidine, AT-halo-synthesis, 7, 246 Azetidine, AT-hydroxy-synthesis, 7, 271 Azetidine, 2-imino-stability, 7, 256 Azetidine, 2-methoxy-synthesis, 7, 246 Azetidine, 2-methyl-circular dichroism, 7, 239 optical rotatory dispersion, 7, 239 Azetidine, AT-nitroso-deoxygenation, 7, 241 oxidation, 7, 240 synthesis, 7, 246 Azetidine, thioacyl-ring expansion, 7, 241 Azetidine-4-carboxylic acid, 2-oxo-oxidative decarboxylation, 7, 251 Azetidine-2-carboxylic acids absolute configuration, 7, 239 azetidin-2-ones from, 7, 263 synthesis, 7, 246... 

The -position of the cyclopropane ring was established by the observed negative circular dichroism curve (Ae — 2.03 in dioxane at 298 m/i) and consideration of the inverse octant rule for cyclopropyl ketones. ... 

The two images may be subtracted to create a difference image that reveals the dichroism directly. The 3D distribution recovered upon inversion, D r, 9), is thus... 

Optical activity in metal complexes may also arise either if one of the ligands bound to the metal in the first co-ordination sphere is itself optically active or if the complex as a whole lacks a centre of inversion and a plane of symmetry. Thus all octahedral cts-complexes of the tris-or bis-chelate type have two isomeric forms related by a mirror plane, the d- and /-forms. These species have circular dichroism spectra of identical intensities but opposite in sign. The bands in the circular dichroism spectrum are, of course, modified if ligand exchange occurs but they are also exceedingly sensitive to the environment beyond the first co-ordination sphere. This effect has been used to obtain association constants for ion-pair formation. There also exists the possibility that, if such compounds display anti-tumour activity, only one of the mirror isomers will be effective. 

The transition from B-DNA to Z-IMA was first observed in solution by the near inversion of the circular dichroism of... 

In spectroscopy the Kramer s Kronig relations are often used. For example the optical rotatory dispersion (ORD) is related to the circular dichroism (CD) through such a pair of transforms.36 Workers in the area usually measure the (CD) and determine the (ORD) through Kramer s Kronig inversion of the (CD). 

Wortmann-Saleh D, Grimme S, Engels B, Miiller D, Vogtle F (1995) A study of the N-inversion barrier and the circular dichroism spectra of l-thia-10-aza[2.2]metacyclophane. J Chem Soc Perkin Trans 2 1185-1189... 

Before discussing the remarkable kinetic inertia of these ternary species it is useful to present the main characteristic of the CuT4-poly-glutamate binary system. The binary complex is chiral and kinetically labile. This is shown by (1) the presence of an induced band in the Soret region of the circular dichroism (CD) spectra (inset of Fig. 3, curve a) and (2) the inversion (in about 10 min) of the same... 

FIGURE 3.15 UV-vis absorption spectra of PMMA films containing (A) diarylethene and (B) spiropyran before (I) and after (2,3) linearly polarized UV irradiation.The probe light was also linearly polarized, and spectra were obtained for both parallel, Abs//, and perpendicular Abs., orientations. The insets in (A) are e>q anded views of both the UV and the visible absorptions of the diarylethene chromophore. identical spectra were obtained for both Abs// and Abs before UV irradiation. For both the diarylethene and spiropyran chromophores, inasmuch as the orientational hole burning and orientational redistribution processes occur with Abs > AbS// within the irradiation wavelength band, note the inversion of the sign of the dichroism between the UV and visible bands of the spectra. After reference 29, redrawn by permission. 

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