Stereochemical descriptor

All introductory organic chemistry texts provide a detailed presentation of the various rules for assigning descriptors to stereocenters. Here we provide a brief review of the terminology to remind the student of the basics. 

Multiple bonds are treated as multiple ligands that is, C=0 is treated as a C that is singly bonded to two oxygens with one oxygen bound to a C. For example, the priorities shown below for the substituted alkene are obtained, giving an E-stereochemistry. 

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The S in S adenosylmethio nine indicates that the adenosyl group is bonded to sulfur It does not stand for the Cahn-Ingold-Prelog stereochemical descriptor... 

As mentioned in the introduction, the first empirical correlation between the absolute configuration of dopants and the handedness of induced cholesterics was proposed in 1975.20 The first attempt to find a general correlation was a few years later Krabbe et al.58 related the sense of the cholesteric to a stereochemical descriptor of the dopant based on the effective volume of the substituents and listed many compounds following this rule. However, exceptions were described at that time,59 and, furthermore, this approach neglects the role of the structure of the nematic solvent in determining the sense of the cholesteric. It is well known that chiral compounds may induce cholesterics of opposite handedness in different nematics.60,61... 

Alternative names are shown in some cases this should emphasize that there is often no unique correct name. Sometimes, it can be advantageous to bend the rules a little so as to provide a neat name rather than a fully systematic one. Typically, this might mean adopting a lower priority functional group as the suffix name. It is important to view nomenclature as a means of conveying an acceptable unambiguous stmc-ture rather than a rather meaningless scholastic exercise. Other examples will occur in subsequent chapters, and specialized aspects, e.g. heterocyclic nomenclature, will be treated in more detail at the appropriate time (see Chapter 11). Stereochemical descriptors are omitted here, but will be discussed under stereochemistry (see Sections 3.4.2 and 3.4.3). 

More complex devices have been developed that are capable of dealing with all cases. The reader is referred to the Nomenclature of Inorganic Chemistry, Chapter 10. The use of stereochemical descriptors in organic names and formulae is dealt with in Chapter 3, Section 3.8 (p. 21). 

The use of stereochemical descriptors in both names and formulae is dealt with in Chapter 3, Section 3.8 (p. 21). 

There are three conceivable rotamers for each diastereomer with different relative orientations of the substituents at the atoms C-l and C-2 (for assigning the stereochemical descriptors the fragment L1-C1-C2-L2 is taken as the longest zig-zag chain)368. The experimental NMR parameters, e.g., 3/h,h> are weighted average values ... 

For assigning the stereochemical descriptors the fragment L1—C1 —C2 —L2 is taken as the longest zig-zag chain. 

A Ba of stereochemical descriptors and structural prefixes nay be found in Table 1-6.)... 

Figure 5 Stereochemical descriptors for (a) chiral tetrahedral compounds, and (b) square-planar complexes...

Figure 6 Stereochemical descriptors for some important types of octahedral complexes...

Since the priority of ligands in stereochemical descriptors is indicated by numbers each ligand has also been given... 

The chiral identity of a molecule is included in the nomenclature of inorganic compounds, and today s comprehensive system is based upon suggestions made in 1990 in IUPAC s Recommendations on Nomenclature of Inorganic Chemistry [84], and ACS s Inorganic Chemical Nomenclature [90]. The basis for the usage of stereochemical descriptors was laid by Brown [91,92], from which three types of chiral descriptor conventions were developed (i) Steering-wheel-convention [93], (ii) Skew-lines convention [94] and (iii) Oriented-skew-lines convention [95]. 

Fig. 12. The four diastereoisomeric 1 1 adducts which can be formed on reaction of the bisdiene 37 with the syn-bisdienophile 38. The stereoelectronic control in operation during the reaction is such that only the syn/endo-H isomer 40 has been detected [21, 38, 110, 112]. The remote stereochemical descriptors, syn and anti, refer to the relative configurations of the endoxide bridges across each newly-formed cyclohexene ring. The close stereochemical descriptors, exo-H and endo-H, refer to the relative configuration adopted by the hydrogen atoms at the ring junctions associated with the newly created chiral centers...

Use plus and minus signs enclosed in parentheses as stereochemical descriptors. 

These symbols are often combined with coordination numbers and position designations for stereochemical descriptors (e.g., OC-6-11 ). 

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