Absolute configuration of chiral molecules

Techniques for determining the absolute configuration of chiral molecules were not developed until the 1950s and so it was not possible for Eischer and his contemporaries to relate the sign of rotation of any substance to its absolute configuration A system evolved based on the arbitrary assumption later shown to be correct that the enantiomers... 

Addadi, L., A Link Between Macroscopic Phenomena and Molecular Chirality, Crystals as Probes for the Direct Assignment of Absolute Configuration of Chiral Molecules, 16, 1. 

Crystals as Probes for the Direct Assignment of Absolute Configuration of Chiral Molecules... 

The use of a reference axial system, whether right- or left-handed, is completely analogous to the Cahn, Ingold, and Prelog convention (75-77) regarding the specification of the absolute configuration of chiral molecules R and S as depicted in Scheme 11 for molecules with large (L), medium (M), and small... 

This approach may also be applied to racemic bilayers built up from homo-chiral Langmuir-Blodgett monolayers. By measuring the two-dimensional diffraction pattern from such a bilayer it is possible to deduce the molecular chirality of each of the two monolayers in the order they were inserted to construct the bilayer. This approach can be extended to multilayers. Thus, in principle, we close the circle started in Section IV-G-1. It is possible to assign the absolute configuration of chiral molecules in centrosymmetric crystals provided that one can construct the crystal (in this case the multilayer) by adding homochiral layers one by one. 

The purpose of this review is two pronged. We have discussed the far-reaching manifestations of molecular chirality in crystals on the macroscopic scale, and have described the various direct methods for the assignment of absolute configuration of chiral molecules in solids. Our analysis has been confined to the solid state, because of the difficulties associated with the direct assignment of absolute configuration in the dispersed phase (12). 

A LINK BETWEEN MACROSCOPIC PHENOMENA AND MOLECULAR CHIRALITY CRYSTALS AS PROBES FOR THE DIRECT ASSIGNMENT OF ABSOLUTE CONFIGURATION OF CHIRAL MOLECULES... 

Secondly, we have labeled one of the substituted methanes 5-fluorochloro bromomethane and the other f -fluorochlorobromomethane. S (sinister, left) and R (rectus, right) are labels that are useful in designating the absolute configuration of chiral molecules in space. The rules for assigning S stereochemistry in one case and R stereochemistry in the other are somewhat complex but it doesn t matter, so never mind. The point is that we have a way of talking about the two possibilities. 

Stephens PJ, Devlin FJ, Pan J-J (2008) The determination of the absolute configurations of chiral molecules using vibrational circular dichroism (VCD) spectroscopy. Chirality 20 643-663... 

Stephens, R J. McCaim, D. M. Cheeseman, J. R. Frisch, M. J. Determination of absolute configurations of chiral molecules using ab initio time-dependent density functional theory calculations of optical rotation how reliable are absolute configurations obtained for molecules with small rotations , Chirality 2005,17, S52-S64. 

Absolute Configuration of Chiral Molecules of the Type CHDRR 10... 

ABSOLUTE CONFIGURATION OF CHIRAL MOLECULES OF THE TYPE CHDRR ... 

L. A link between macroscopic phenomena and molecular chirality crystals cis prohes for the direct assignment of absolute configuration of chiral molecules. Topics in Stereochemistry 16, 1-85 (1986). 

M., and Leiserowitz, L. Centrosymmetric crystals for the direct assignment of the absolute configuration of chiral molecules. Application to the a-amino acids by their effect on glycine crystals. J. Amer. Chem. Soc. 105, 6615-6621 (1983). 

Addadi, L., Berkovitch-Yellin, Z., Weissbuch, 1., Lahav, M., Leiserowitz, L., and Weinstein. S. The use of enantiopolar directions in centrosymmetric crystals for direct assignment of absolute configuration of chiral molecules application to the system serine/threonine. J. Amer. Chem. Soc. 104, 2075-2077 (1982). 

The mirror-image relationship of the CD spectra of enantiomers is the key to the determination of the absolute configuration of chiral molecules using CD spectroscopy. 

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