Sequence Rule system

Sequence rule (Section 7 6) Foundation of the Cahn-Ingold-Prelog system It is a procedure for ranking substituents on the basis of atomic number... 

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). 

The compound is named as a disubstituted deoxy sugar. Configuration is determined by regarding the substituent having priority according to the Sequence Rule ([13], Section E), as equivalent to OH. Any potential ambiguity should be dealt with by the alternative use of the R,S system to specify the modified stereocentre. 

The system that has replaced the dl system is the Cahn-Ingold Prelog system, in which the four groups on an asymmetric carbon are ranked according to a set of sequence rules. For our purposes, we confine ourselves to only a few of these rules, which are sufficient to deal with the vast majority of chiral compounds. 

R. S. Cahn (England), C. K. Ingold (England), and V. Prelog (Switzerland) devised the (R-S) system (Sequence rule) for designating the configuration of chiral carbon atoms. 

Similar systems in which a higher level of suhstitution exists may be treated analogously if the erythro or threo designation is employed to denote the relative placements of those two substituents, one for each backbone carbon atom, which rank highest according to the Sequence Rule. Thus, the following hypothetical examples would be designated as indicated ... 

Within the CIP system these general criteria are expressed as five Sequence Rules. These are... 

In the areas of coordination and metalorganic compounds the CIP system was adopted in part (Sequence Rules), but a variety of special conventions mainly concerning constitution and descriptor assignment rules for stereogenic centers with more than four ligands have emerged. An excellent review is available1, and here only those types of compounds relevant to this volume are discussed. 

However, for the reason already outlined (see Section 1,1.8.) some chemists do not like this system and try to avoid it. As the descriptors are based on the CIP sequence rules, which in turn are based on atomic material properties, i.e., the atomic and mass number, the system cannot in general express genetic relationships within a collection of related compounds and throughout the complete range of reactants undergoing a given reaction. Unfortunately, reconciliation of the conflicting demands is impossible. 

Cahn, R. S. An introduction to the sequence rule. A system for the specification of absolute configuration. J. chem. Education 41, 116... 

A system that is easy to use and which is based on the sequence rules already described for the R,S system works as follows ... 

In most chemical processes reactors are sequenced by systems that separate the desired products out of their outlet reactor streams and recycle the unconverted reactants back to the reactor system. Despite the fact that process synthesis has been developed into a very active research area, very few systematic procedures have been proposed for the synthesis of reactor/separator/recycle systems. The proposed evolutionary approaches are always based upon a large number of heuristic rules to eliminate the wide variety of choices. Many of these heuristics are actually extensions of results obtained by separately studying the synthesis problem of reactor networks or separator systems, and therefore the potential trade-offs resulting from the coupling of the reactors with the separators have not been investigated. 

Sequence Rules for Geometric Isomers and Chiral Compounds. Although cis and trans designations have been used for many years, this approach becomes useless in complex systems. To eliminate confusion when each carbon of a double bond or a chiral center is... 

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