Local stereochemistry

Backscattered dual circular polarization results on ephedrine and its stereoisomers are reported by Yu et al. (1993). All four stereoisomers examined show very similar Raman spectra, but their ROA spectra nicely show the sensitivity of ROA to the configurations and conformations of the molecules. As the features observed seem to be connected to the local stereochemistry, it seems to be possible that in the near future, with some more experimental data at hand, to deduce the absolute configuration of molecules of unknown stereochemistry directly from the ROA spectra. 

Wen et al. (1993) showed the ROA spectra of 15 monosaccharides in aqueous solution. They found three main regions of interest, were ROA spectra should provide insights into local stereochemistry. The first is the region of 750 to 950 cm reflecting anomeric configuration, the second at 950 to 1200 cm gives information about ring structure and... 

Indicator variables taking into account, for instance, position occupancy, bond presence and/or local stereochemistry. 

The majority of the work on the fundamental processes of photodegradatlon of acrylic polymers has been carried out by Grassle and co-workers (5-7). For radiation with wavelength X > 300.0 nm photodegradatlon is initiated by absorption of a photon by the carbonyl group of the ester side chains. Subsequent fragmentation depends on local stereochemistry and temperature. The principal modes of fragmentation are described by the Norrish I and Norrish II processes ( ). 

Randall et al. s functional group survey (83) included a number of transition metal carbonyl complexes (Table XL). The authors showed that SCO depended on the local stereochemistry of the metal atom, for example, compare octahedral-(CO)sCrC(OMe)(Me) CO-ciy 217. 6 ppm CO-trans 223.6 ppm with pyramidal-(CO)3(aC5Hs)WMe CO-cis 239.2 ppm CO-trans 217.8 ppm. An additional factor influencing the carbonyl resonance was found to be the steric and electronic requirements of the other ligands in the complex. 

The term describes the substitution pattern and the local stereochemistry. R leads to... 

Through ligand-field theoretical results and new knowledge about local stereochemistry around central atoms, these accomplishments have led to the use of atomic electron configurations as one of the most important classificatory tools in inorganic chemistry. This is the key point of this paper together widi its further illustration of how qualitative results, based upon atomic electron configurations, can be quantified. 

Again, data for c/s-heterovinylene sets were first correlated with the extended Hammett equation by Charton and Charton (73). There are three sets of data extant in the literature, all for oximes. The sets studied are set forth in Table XXVII (sets 274 through 27-6). Results of the correlations and values of pj are reported in Tables XXVIII and XIX, respectively. Of the three sets studied, two did not give significant correlation. The stereochemistry of the antt-acetyl ketoximes is discussed by Charton and Charton (73). It would seem that the localized effect is predominant in the case of the c/s-heterovinylene sets. 

The chelate effect in proteins is also important, since the three-dimensional (3-D) structure of the protein can impose particular coordination geometry on the metal ion. This determines the ligands available for coordination, their stereochemistry and the local environment, through local hydrophobicity/hydrophilicity, hydrogen bonding by nearby residues with bound and non-bound residues in the metal ion s coordination sphere, etc. A good example is illustrated by the Zn2+-binding site of Cu/Zn superoxide dismutase, which has an affinity for Zn2+, such that the non-metallated protein can extract Zn2+ from solution into the site and can displace Cu2+ from the Zn2+ site when the di-Cu2+ protein is treated with excess Zn2+. 

In part (a) D-amino acids are underlined a broken line indicates either that the stereochemistry of the amino acid has not been determined or that a specific amino acid occurs both in the D- and the L-form, but a localization of the the two enantiomers has not been effected. In part (b) D-amino acids are indicated only when data are available Irom the literature... 

This tree is common in the Chapare region of Bolivia, and is locally used for the treatment of leishmaniasis (214). Although, janetine (235) was isolated from Nature in its optically active form [aJo +8 (c 0.95, EtOH), the absolute stereochemistry is not known (214). In 1958, Schmutz and Hunziker reported the isolation of 3,4-dihydroellipticine (M-alkaloid D) (236) from A. ulei (207). Three years later, the same authors reported the isolation of the same alkaloid, 3,4-dihydroellipticine (236) along with 3,4-dihydroolivacine (237) as an inseparable mixture... 

The exact local magnetic field acting on a given nucleus is dependent on its electronic environment, i.e., the kind and number of the surrounding atoms determine its chemical shift (<5), and stereochemistry plays an important role22. <5 Values in this section are referenced to commonly agreed standards tetramethylsilane for 2H and 13C, ammonia for 15N, water for l70, and 85% aqueous phosphoric acid for 31P. 

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