Rotatory dispersion curves

The optical rotatory dispersion curves of steroidal ketones permit a distinction to be made between the conformations, and assignment of configuration is possible without resorting to chemical methods (see, e.g. ref. 36) which are often tedious. The axial halo ketone rule and, in the more general form, the octant rule summarize this principle and have revealed examples inconsistent with the theory of invariable axial attack in ketone bromination. 2-Methyl-3-ketones have been subjected to a particularly detailed analysis. There are a considerable number of examples where the products isolated from kinetically controlled brominations have the equatorial orientation. These results have been interpreted in terms of direct equatorial attack rather than initial formation of the axial boat form. 

The P configuration at C-6 is based on mechanistic considerations and analysis of optical rotatory dispersion curves. 

Since the optical purity of the starting materials and the molar rotations of the pure optically active products are unknown, it is not possible to assay any partial racemization. In most instances the molar rotation of the products is as large as or larger than the starting material. It is probable that no racemization took place in these reactions, but it is impossible to state this unequivocally without a knowledge of the relationship between the rotatory dispersion curves and visible spectra of the products and starting materials. 

A comparison of the rotatory dispersion curves of (+ )s46[Co-( — )-PDTA] and ( + )546[Co-( —)-CDTA] indicates that these ions have the same configuration around the cobalt ion (25). It follows then that (- cyclohexane-diamine has the configuration of Fig. 8. These procedures for fixing configurations will be utilized in subsequent sections for studying the properties of the conformations. 

Photomutarotation, in addition to inversion of the rotatory dispersion curves, is observed on exposure of ( —)-2-chloro-nitrosocamphane (LXXXIX) to intense light.114,187 On the other hand, isomerization of the normal iso-type without the inversion of the rotatory dispersion curves is involved in the case of 2-chloro-2-nitroso derivatives of pino-camphane (XC), carane (XCI), and p-menthane (XCII).116... 

Theoretical calculations of the rotatory dispersion curves for molecules require knowledge of the magnetic-dipole transition integral M between two states, tpi and tpz This integral is M = -i/3 x... 

Like other phenomena involving interactions between electromagnetic radiation and organic molecules, as in infrared, ultraviolet, and nmr spectroscopy, optical rotatory dispersion curves often are quite sensitive to small changes in structure. As an example, the rotatory dispersion curves for enantiomers of cis- and trcMr-lO-methyl-2-decalones, 16 and 17, are reproduced in Figure 19-7 ... 

Figure 19-7 Rotatory dispersion curves for c/s-10-methyi-2-decalone, 16, and trans-10-methyl-2-decalone, 17. (By permission from C. Djerassi, Optical Rotatory Dispersion, McGraw-Hill Book Co., New York, 1960.)...

This means that the molar extinction coefficients of the two enantiomers (e, and er) are unequal in circularly polarized light. These differences in absorption (e, and er) can be measured as a function of wavelength, and the curves obtained are called circular dichroism curves. They have positive or negative signs (Cotton effect) just as for optical rotatory dispersion curves. 

Many rotatory dispersion curves have been obtained for optically active ketones derived from steroids and triterpenes, which are monocyclic, bicyclic, and open-chain compounds. Enough data have been accumulated so that the various shapes and magnitudes of the curves are recognized as characteristic of particular structural features. A good illustration is provided by the rotatory... 

Rotatory dispersion curves often are helpful in establishing configurations thus the relative configurations of compounds 18 and 20a must be the same because, if they were not, the two curves would resemble mirror images of one another. Therefore, if the absolute configuration of 18 corresponds to the formula shown, then compound 20a has the configuration shown and not 20b. 

Dihydrobenzo[6]thiophene-2-carboxylic acid has been resolved212 the levorotatory enantiomer exhibits a plain negative rotatory dispersion curve which allows it to be assigned a D-configura-tion.218 The corresponding 3-carboxylic acid could not be resolved.212... 

T. Okuda, S. Harigaya, and A. Kayomoyo, Studies on optical rotatory dispersion of five-member sugar-lactones configuration and signal of an optical rotatory dispersion curve, Chem. Pharm. Bull. (Tokio), 12 (1964) 504-506. 

Figure 4. Optical rotatory dispersion curves as would be...

Karrer and Meyer25 showed that the rotatory dispersion curve of the copper salts of glucosaminic and chondrosaminic acids bore a close resemblance to those of the D-amino acids but differed considerably from those of the L-amino acids. Replacement of the amino group by a hydroxyl residue did not produce any change since both D-gluconic and D-galactonic acids resemble the D-amino acids in their rotatory dispersion.23... 

XLVII) showed complete identity by IR-spectra and by chromatography, while the rotatory dispersion curves of (+ )-XLVI and (— )-XLVI were mirror images of one another, demonstrating that the two compounds were enantiomeric at all four centers. Pyrifolidine is thus one of a small group of indole alkaloids which exist in both enantiomeric... 

Correlations have also been established between the rotatory dispersion curves of yohimbone (IX) and a tricyclic ketone (X) of known absolute configuration (4). The symmetry of the curves suggests a trans junction of rings D/E and the a-configuration at C-15. 

Baker trans rule or the Hudson isorotation rules have to be taken with care in view of some anomalies.11,38,39 Nuclear magnetic resonance spectra 38 and optical rotatory dispersion curves 38,40,41 have been recently applied to determine the configuration of pyrimidine nucleosides at the anomeric center. 

Palytoxin is a white, amorphous, hydroscopic solid that has not yet been crystallized. It is insoluble in nonpolar solvents such as chlorophorm, ether, and acetone sparingly soluble in methanol and ethanol and soluble in pyridine, dimethyl sulfoxide, and water. The partition coefficient for the distribution of palytoxin between 1-butanol and water is 0.21 at 25°C based on comparison of the absorbance at 263 nm for the two layers. In aqueous solutions, palytoxin foams on agitation, like a steroidal saponin, probably because of its amphipathic nature. The toxin shows no definite melting point and is resistant to heat but chars at 300°C. It is an optically active compound, having a specific rotation of -i-26° 2° in water. The optical rotatory dispersion curve of palytoxin exhibits a positive Cotton effect with [a]25o being -i-700° and [a]2,j being +600° (Moore and Scheuer 1971 Tan and Lau 2000). 

Raney nickel) of the potassium salt of D-xy/o-5-hexulosonic acid oxime produces a mixture of 5-amino-5-deoxy-L-idonic and -D-glu-conic acid in the ratio of 2 1, which is converted into the methyl ester hydrochloride. Upon treatment with alkali, spontaneous cyclization to the pair of 1,5-lactams occurs. 5-Amino-5-deoxy-L-idono-l,5-lactam and 5-amino-5-deoxy-D-glucono-l,5-lactam were separated by recrystallization. The optical rotatory dispersion curves of both compounds were discussed. A new type of lactam, namely, 2-enamino-N,N -bis[(p-methoxycarbonyl)phenyl]-4-(D-gaiacfo-penta-acetoxypentyl)-4-butanelactam was prepared by tbe reaction of 5,6,7,8,9-penta-0-acetyl-3,4-dideoxy-D-ga/ocfo-nonulos- rcns-3-en-l-onic acid with methyl p-aminobenzoate. 

Fig. 2.—Optical Rotatory Dispersion Curves for 5-Amino-5-deoxy-a-i>-xylopyranoses and Their Methyl Glycosides. [Concentrations, 1 mg./ml. in water (left diagram), and...

Reaction Mechanisms. Bailar (2 3) studied the formation of [Co (en) 2003]" from optically active m-[Co(en)2Cl2] and found that products of opposite configurations were obtained under different conditions. He proposed a Walden type inversion for the substitution process. The configurations of the original complex and the products were related using optical rotatory dispersion curves. Dwyer (19) studied these reactions in detail and concluded that the inversion occurs through a trans displacement process involving both Ag+ and OH ... 

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