ORD and CD spectra

Considerably less is known about the chemistry of palladium and platinum 1,1-dithio complexes. Of late, there has been only one report that dealt with the synthesis of a large number of palladium dithiocar-bamates 392). Twenty-five yellow palladium dithiocarbamate complexes were obtained by reaction of PdCla with NaR2dtc in methanol solution. Several other reports have appeared in which a few dithiocarbamate complexes of palladium were synthesized. Thus, the novel [Pd (OH)2dtc 2], which is soluble in water, was isolated 393). The synthesis of optically active palladium(II) complexes of AT-alkyl-a-phen-ethyldithiocarbamates, similar to (XXIV), via the reaction between the optically active amine, CS2, and PdCl2, has been described. From ORD and CD spectra, it has been established that the vicinal contribution of a remote, asymmetric carbon center could give rise to optical activity of the d—d transitions of palladium 394). Carbon disulfide has been shown to insert into the Pt-F bond of [PtF(PPh3)3]HF2, and X-ray studies indicated the structure (XXIX). 

Feringa and Wynbeig (195) have prepared two chiral twisted ethylenes, cis-and fra/w-l,I 2,2 3,3 -hexahydiobiphenanthrylidene (133 and 134). They could be resolved (133 only partly) by HPLC on alumina impregnated with TAPA fa-(2,4,5.7-tetranitrofluorenylideneaminooxy)propionic acid] (196), and UV, ORD, and CD spectra are reported. A slow cis-trans isomerization is mentioned but... 

Detailed discussions of ORD and CD spectra of chiral sulfur compounds may be found in the reviews of Laur (7) and Ziffer (231). 

The validity of the octant rule is supported largely and convincingly by ORD and CD spectra from numerous examples where the dissymmetric perturbers (the groups perturbing the carbonyl chromophore in a nonsymmetric way), such as the methyl group of... 

The structure of brunsvigine (583) has been established by the X-ray analysis of the corresponding 0,0 -di-p-bromobenzoate (7a). Furthermore, the H-NMR spectra of brunsvigine together with several of its derivatives have been completely assigned, and the ORD and CD spectra of these compounds have been measured. The structure of 583 was related to other 5,1 lb-methanomorphanthri-dine alkaloids by methylation and other chemical transformations including a series of Hoffmann degradations (7b). 

The absolute configuration of piperidine Lythrum alkaloids was established by analysis of ORD and CD spectra of biphenyl compounds. 

Haga et al. (1983) have measured the ORD and CD spectra of as2-casein in Ca2+-free phosphate buffer, pH 7.2, and estimated the content of a helix to be about four times as large as in aSi-casein, which they attribute to the lower proline content of the more phosphorylated protein. There are marked differences in the primary and predicted secondary structures of aS2-type caseins from different species. One notable constant feature, however, is a predicted a helix... 

Rigorously, ORD and CD spectra are related through the Kronig-Kramers theorem, a well-known general relationship between refraction and absorption, i.e. nL - nR is determined by eL - % for A from zero to infinity [128], (The analogous relationship between refraction and reflection applies to cholesteric liquid crystals.) Hence, in order to maximize ORD in the transparent region, Cotton effects, associated with exciton coupling (both intramolecular and intermolecular), have... 

Several reports on ORD and CD spectra for (-)-morphine have been published/406 410 When no carbonyl group is present in ring C, 4,5-epoxymor-phinans exhibit a negative Cotton effect at about 280 nm, and a positive one around 254 nm associated with the aromatic chromophore/407 ... 

Related compounds with a B/C trans junction have ORD and CD spectra similar to their B/C cis isomers, reflecting the configuration at C-13 rather than at C-14. 

Circular dichroism is usually observed only in the vicinity of an absorption band, a positive Cotton effect showing a positive peak at the absorption maximum and a negative effect showing a negative peak. This simple spectrum makes CD more selective and easier to interpret than ORD. With improvements in instrumentation, it has become the method of choice for studying chiral complexes. Both ORD and CD spectra are shown in Figure 9-20. 

Fig. 27. ORD and CD spectra of ( )-(—> cyclooctene 55 (in cyclohexane). Octant projection along the Z axis background octant signs in brackets ...

The absolute configuration of other heterohelicenes has been correlated by comparison of their ORD and CD spectra (-l-)-heterohelicenes generally have P screw sense. 

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