Stereoisomers claims

In the desulfurization of 3-substituted thiophenes several stereoisomers may be formed in certain cases. Both meso and racemic compounds have been obtained from the desulfurization of 3,4-diaryl-substituted thiophenes. It is claimed, however, that only meso, -diphenyladipic acid is obtained upon desulfurization of 3,4-di-phenyl-2,5-thiophenedicarboxylic acid and only di-isoleucin from 3-thienylglycine. The formation of small amounts of dimeric products in the desulfurization has been discussed with reference to the mechanism of this reaction. ... 

The mammalian olfactory system possesses enormous discriminatory power. It is claimed that humans can perceive many thousands of different odorous molecules, termed odorants. Even slight alterations in the structure of an odorant can lead to profound changes in perceived odor quality. One commonly cited example is carvone, whose L- and D-stereoisomers are perceived as spearmint and caraway, respectively. However, more subtle molecular alterations can also generate striking changes in perception. 

The claimed lack of ambiguity does not preclude a physical overlap between elements. If one chooses to regard as stereoisomers the three nonsuperposable staggered forms resulting from the torsion of a carbon-carbon bond with six different ligands, we have three separate elements of stereoisomerism, two centers and one line. This is the minimum number required to account for the existence of the 12 stereoisomers. 

Complexation with racemic 2,3-di(4-aminophenyl)butane (L) gave Ag(L)3N03, which was claimed to be six-coordinate with the silver bound to the six donor atoms. By comparison, the meso stereoisomer gave only a 1 1 complex AgN03. 

Preparation of the two stereoisomers of perhydro-9b-boraphenalene was originally reported by Koster and Rotermund,6 and the present procedure (part A) is largely based on the procedure described by these authors. However, the original stereochemical assignment was incorrect and has been reversed.3 7 Furthermore, these authors did not use the thermal treatment described above, which appears essential to achieve isomerization of other constitutional isomers into perhydro-9b-boraphe-nalene.3 The original procedure for isomerization of the cis,trans isomer to the all cis isomer has been satisfactory. Contrary to the claim made by these authors,6 however, this isomerization does not lead quantitatively to the all cis isomer, but reaches an equilibrium, which consists of the all cis and cis,trans isomers in the ratio of 88 12 this ratio was also confirmed by reverse isomerization of the pure all cis isomer.5... 

To achieve this goal, (—)-carvone was transformed into the dimethylhydrazone, and the unsaturated hydrazone was deprotonated by EDA (Scheme 37). Due to complexation of the lithium ion with nitrogen, 3,3-dimethoxypropyl bromide was used to alkylate the a-position (202). A 3 2 mixture of the two possible stereoisomers 332 and 333 was obtained. The authors claimed that the ketone was... 

A method of quantitatively determining mole fractions of stereoisomers by IR differential absorbance measurements has been described by Gendreau and Griffiths (1976). Absorbance spectra of the pure isomers at a certain concentration are subtracted from the absorbance spectrum of the mixture at the same concentration. The method is claimed to be accurate even if the analytical bands of the isomers have different absorption coefficients or half-widths. 

Compounds 144 containing a 2,3-epoxy and 2,3-epithiocyclohexyl substituents were synthesized and claimed as herbicidal compounds <1992US5169426, 1985EP0172502>. Although they potentially possess multiple stereoisomers, which presumably display different potency, the stereochemical details were not provided. 

A word of caution should be added with respect to Chemical Abstracts, as far as chirality assignments of homoannular substituted ferrocene derivatives are concerned. Until the 8th collective index, only (-f) and (—) are found as chirality indicators. For quite a long time, no descriptors were given at all, only the remark stereoisomer , followed by the registry number, which does not allow identification of a compound easily. This fact is in sharp contrast to the claims of Chemical Abstracts Service authors that they would consequently use Schlogl s central descriptors [20, 21]. Since volume 114, the (R, S ) nomenclature for ferrocene derivatives begins to appear, but its application is not very consequent, at least at the time where the book was written, and it is advisible to examine the orginal article rather than trust Chemical Abstract s descriptors. 

CsHzzNOf 176.278 Present in Amanita muscaria. Mp 129-131° dec. (as tetrachloroaurate). [a]u +20.5 (tetrachloroaurate). Stereochem. of the nat. prod, could not be eonfinned. It was claimed to have the erythro-conSig.. but props, do not coincide with those of the well-characterised synthetic stereoisomers later obt. 

A route to ketofuranosides by way of enol ether derivatives and their epoxidation is illustrated in Scheme 2, but the procedure affords Z and E alkenes and stereoisomers following the opening of their products of epoxidation. The authors, nevertheless, claim moderate to good yields, good stereoselectivities and separable products and rationalise the... 

Ultraviolet and Infrared Spectra.—The effect of conjugation in the excited state of some silicon-substituted thiophens has been discussed. The u.v. and i.r. characteristic absorption spectra of some pairs of cis- and rra/75-isomers of 2 - and 3 -substituted 2-styrylthiophens have been determined. It is claimed that the spectra of the stereoisomers are sufficiently different to assign the configuration. The i.r. and Raman spectra of 4-chloro-, 4-bromo-, 4-iodo-, and 4-cyano-2-fluoro-thiophens have been studied in the region 500—540 cm . The fundamental frequencies have been assigned, and normal co-ordinate calculations have been performed. The force constants were adjusted to reproduce accurately the fundamental frequencies. Thermodynamic functions and mean amplitudes of vibration for these molecules were also calculated. Thiophen-2-aldehyde and 19 related aldehydes have been studied under high resolution in the i.r. C=0 region. 

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