R-configuration

The diagram shows the method applied to butan-2-ol, for which the laevorotatory ( —) isomer is known to have the (R)-configuration. 

As outlined m Table 7 1 (+) 2 butanol has the S configuration Its mirror image IS (—) 2 butanol which has the R configuration... 

This compound therefore has the R configuration It is (/ ) (+) 2 methyl 1 butanol... 

To verify that the Fischer jjrojection has the R configuration at its chirality center rotate the three dimensional representation so that the lowest ranked atom (H) points away from you Be careful to maintain the proper stereochemical relationships during the operation... 

Make a molecular model corresponding to the stereochem istry of the Fischer projection of 2 phenyl 2 butanol shown in the equation and verify that it has the R configuration... 

Chemical Properties. Because of its chiral center, malic acid is optically active. In 1896, when tartaric acid was first reduced to malic acid, the levorotatory enantiomer, S(—), was confirmed as having the spatial configuration (1) (5,6). The other enantiomer (2) has the R configuration. A detailed discussion of configuration assignment by the sequence rule or the R and S system is available (7). 

Each reaction in the sequence shown is reported to proceed with retention of configuration, yet the starting material has the R configuration and the product has the S configuration. Reconcile this apparent contradiction. 

D-Amino acid oxidase will oxidase only serine having the R configuration at C-2. Glycolate oxidase will remove only the prv-R hydrogen of glycolic acid Does the product (0=CHC02H) contain tritium Explain your reasoning. 

In Problem 4.25 you were asked to draw the preferred conformation of menthol on the basis of the information that menthol is the most stable stereoisomer of 2-isopropyl-5-methylcyclo-hexanol. We can now completely describe (—)-menthol structurally by noting that it has the R configuration at the hydroxyl-substituted carbon. 

Recendy, Darzens reaction was investigated for its synthetic applicability to the condensation of substituted cyclohexanes and optically active a-chloroesters (derived from (-)-phenylmenthol). In this report, it was found that reaction between chloroester 44 and cyclohexanone 43 provided an 84% yield with 78 22 selectivity for the axial glycidic ester 45 over equatorial glycidic ester 46 both having the R configuration at the epoxide stereocenter. 

One further point needs to be mentioned—the matter of absolute configuration. How do we know that our assignments of R,S configuration are correct in an absolute, rather than a relative, sense Since we can t see the molecules themselves, how do we know that the R configuration belongs to the dextrorotatory enantiomer of lactic acid This difficult question was finally solved in 1951, when J. M. Bijvoet of the University of Utrecht reported an X-ray spectroscopic method for determining the absolute spatial arrangement of atoms in a molecule. Based on his results, we can say with certainty that the R,S conventions are correct. 

In (a), you would be located in front of the page toward the top right of the molecule, and you would see group 2 to your left, group 3 to your right, and group 1 below you. This corresponds to an R configuration. 

Problem 26.2 Of the 19 l amino acids, 18 have the 5 configuration at the a carbon. Cysteine is the only i. amino acid that has an R configuration. Explain-... 

Cysteine is the only amino acid that has I. stereochemistry but an R configuration. Make up a structure for another i amino acid of your own creation that also has an R configuration. 

The stereoisomer of CHFCIBr shown in Figure A8.1 has the R configuration, whereas that of alanine has the S configuration. 

Addition of metalated, enantiomerically pure a-sulfinyl dimethylhydrazones (e.g., 9) to racemic a-chiral aldehydes 10 proceeds with good to excellent diastereo- and enantioselectivi-ty12. Diastereomeric ratios increase with increasing steric demand of the acetaldehyde substituent R1 compared to the methyl group, and each diastereomer is obtained with high enantiomeric excess. In the aldol-lype addition to 2-phenylpropanal, one of the four possible stereoisomers is formed selectively. The relative (syn) and absolute (R.R) configuration is in accord with Cram s and related rules as well as H-NMR data of closely related compounds. 

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