Chiral molecules relative configurations

In Section 7.5, the term relative configuration was used to describe the stereochemical relationship between a single chirality center in one molecule to a chirality center in a different molecule. Relative configuration is also used to describe the way multiple chirality centers within the same molecule are related. The two erythro stereoisomers of 2,3-dihydroxybutanoic acid possess the same relative configuration. The relationship of one chirality center to the other is the same in both, but different from that in the threo stereoisomer. 

Erythro and three describe the relative configuration (Section 7 5) of two chirality centers within a single molecule... 

As shown for the aldotetroses an aldose belongs to the d or the l series accord mg to the configuration of the chirality center farthest removed from the aldehyde func tion Individual names such as erythrose and threose specify the particular arrangement of chirality centers within the molecule relative to each other Optical activities cannot be determined directly from the d and l prefixes As if furns ouf bofh d eryfhrose and D fhreose are levorofafory buf d glyceraldehyde is dexfrorofafory... 

The two stereoisomeric furanose forms of D-erythrose ae naned a-D-erythro-furanose and p-D-erythrofuranose. The prefixes a and p describe the relative configuration of the anorneric cabon. The configuration of the anorneric cabon is cornpaed with that of the highest numbered chirality center in the molecule—the one that determines whether the cabohydrate is d or l. Chemists use a simplified, informal version of the lUPAC rules for assigning a and p that holds for ca bohydrates up to and including hexoses. 

Erythro (Section 7.11) Term applied to the relative configuration of two chirality centers within a molecule. The erythro stereoisomer has like substituents on the same side of a Fischer projection. 

Before 1951 only relative configuration of chiral molecules were known. 

It must not be forgotten that the concept of pure substance, referred to earlier, is very rigorous and must take into account, not just the constitution and relative configuration of a molecule, but also the absolute configuration of each chiral center that may present. For example, again in relation to quinine (i), quinidine (2) is also known and the only difference between the two molecules is the disposition in space of the groups bonded to C(8). Nevertheless 2 is a different molecule and shows no antimalarial activity. In addition, only one enantiomer of quinine (1), the laevorotatory, corresponds to the natural compound and manifests the specific physiological properties associated with this substance. 

These chiral building blocks are incorporated into the target molecules in such a way that the configuration at the stereo centers remains unchanged. Since the relative configuration of newly produced centers of chirality can be controlled, virtually any enantiomerically pure product can be built around the chiral starting molecule. In the case of pheromones, chirality has a similar influence on their biological activity while one enantiomer attracts the insect species, the other may act as a repellent. ... 

In considering the retrosynthetic analysis of juvabione, two factors draw special attention to the bond between C-4 and C-7. First, this bond establishes the stereochemistry of the molecule. The C-4 and C-7 carbons are both chiral, and their relative configuration determines which diastereomeric structure will be obtained. In a stereocontrolled synthesis, it is necessary to establish the desired stereochemistry at C-4 and C-7. The C(4)—C(7) bond also connects the side chain to the cyclohexene ring. Because a cyclohexane derivative would make a logical candidate for one key intermediate, the C(4)—C(7) bond is a potential bond disconnection. 

When there are several chiral carbons in a molecule, the configuration at one center usually is related directly or indirectly to glyceraldehyde, and the configurations at the other centers are determined relative to the first. Thus in the aldehyde form of the important sugar, (+)-glucose, there are four chiral centers, and so there are 24 = 16 possible stereoisomers. The projection formula of the isomer that corresponds to the aldehyde form of natural glucose... 

In response to this nomenclature dilemma, the Cahn-Ingold-Prelog (IUPAC, International Union of Pure and Applied Chemistry) system of nomenclature was developed and is now the standard mediod to specify the relative configuration of chiral centers in molecules. Each chiral center will have two possible mirror-image configurations, which are designated as eidter R or S. 

Indicate the chiral centers in die following molecules and give the relative configuration (R,S) of each ... 

RDCs are commonly used for the structure elucidation of proteins and nucleic acids nowadays. Only recently the approach was transferred back to also obtain structural information of small- to medium-sized organic molecules. The central application in this case is the determination of relative configurations of distant chiral and prochiral centres, and also conformational studies of biologically active molecules, for example the enantiomeric differentiation of small molecules in chiral alignment media can be achieved. 

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