Rotatory dispersion Pfeiffer

Since Werner s pioneering work on optical activity in complex inorganic compounds there have been many important developments in the field. One of the more interesting of these is known as the Pfeiffer effect which is a change in the optical rotation of a solution of an optically active substance e,g, ammonium d-a-bromo-camphor-T-sulfonate) upon the addition of solutions of racemic mixtures of certain coordination compounds (e,g, D,L-[Zn o-phen)z](NOz)2, where o-phen = ortho-phenan-throline). Not all combinations of complexes, optically active environments and solvents show the effect, however, and this work attempts to apply optical rotatory dispersion techniques to the problem, as well as to determine whether solvents other than water may be used without quenching the effect. Further, the question of whether systems containing metal ions, ligands, and optically active environments other than those already used will show the effect has been studied also,... 

In this work the authors have attempted to expand the scope of the Pfeiffer effect to other systems and solvents and to determine unambiguously the source of the effect. To this end they applied optical rotatory dispersion techniques as a tool in their study. 

Because the Pfeiffer effect is exhibited by tris(l,10-phenanthroline)-nickel(II) ion and d-a-bromocamphor-7r-sulfonate and, because the complex has an absorption band in the visible region, this system was studied using optical rotatory dispersion techniques. The study revealed that the optical rotatory dispersion curves showing Pfeiffer rotation vs. wavelength were very similar to that of the resolved complex (Figures 3 and... 

Figure 3. Comparison of the optical rotatory dispersion and the Pfeiffer rotation of [Ni o-phen)Jp ...

Figure 1 shows the Pfeiffer Effect for the racemic complex [Cr(C20/j,) 3] " in the presence of d-cinchoninium chloride, and this figure also provides strong support for the equilibrium displacement mechanism described above. It should be noticed that the optical rotatory dispersion (ORD) of the complex in the Pfeiffer Effect (Figure 1) is essentially the same as that of the pure enantiomer resolved by conventional means, and it shows a marked Cotton Effect. Since the environment substance itself shows only a plain or normal optical rotatory dispersion in the visible region, the ORD in the Pfeiffer experiment must be due to an excess of one enantiomer of the complex over the other - which is what is postulated to occur in the equilibrium displacement mechanism. 

Figure 1. (A) Optical rotatory dispersion of (- -)D-[Cr(C2Oi)3]3 in water at 23°C (B) Pfeiffer rotatory dispersion of d,l-7Cr( C2Oij373" in water at 23°C with d-cinchoninium chloride.

It is also important to note that the Pfeiffer Rotatory Dispersion and the Pfeiffer Circular Dichroism of a given complex enantiomer (e.g.,... 

Stan s some one hundred articles dealt with the synthesis, structure, stereochemistry, and biological properties of coordination compounds, including the anticancer activity of platinum complexes optical rotatory dispersion circular dichroism the Pfeiffer Effect in metal complexes inorganic nomenclature and the application of computer techniques to chemical and information problems. A prominent educator, he edited three books on inorganic and coordination chemistry. 

OPTICAL ROTATORY DISPERSION, CIRCULAR DICHROISM, AND THE PFEIFFER EFFECT IN COORDINATION COMPOUNDS... 

During the past decade there has been a considerable resurgence of interest in the optical rotatory dispersion and circular dichroism of coordination compounds. In addition, there also has been a considerable renewal of interest in the Pfeiffer effect during this same period of time. This coincidental renewal of interest in these fields is most fortunate, because it is possible to apply optical rotatory dispersion and circular dichroism techniques to the study of the Pfeiffer effect with fruitful results vide infra). 

If the Dwyer and Gyarfas proposal for the existence of an equilibrium between optically labile enantiomers exists, and if this equilibrium is displaced in the presence of an optically active environment, then a study of the optical rotatory dispersion and circular dichroism in the visible region of a Pfeiffer-active colored complex (in the presence of a colorless, optically active environment) should yield ORD and CD curves which are similar to those obtained for the pure, resolved enantiomers of these complexes. That this is actually the case is shown in Figs. 9 and 10, which give the... 

Fig. 15. Drude plots of cinchonine (C), cinchonine with [Zn(phen)3] and the resulting Pfeiffer rotation (P). Rotatory dispersion data for C and CZ taken from Fig. 14.

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