Sequence Rules for Specification of Configuration

Drawings of sodium ammonium tartrate crystals taken from Pasteur s original sketches. One of the crystals is right-handed and one is left-handed.  

Louis Pasteur (1822-895) was bom at Dale, the son of leather tanners. After receiving his doctorate from the Ecole Nor-male Superieure at age 25, his landmark discovery of tartaric acid enantiomers was made only one year later. Pasteur is best known for his studies in bacteriology and for his discovery of vaccines for anthrax and rabies. 

we would describe Pasteur s work by saying that he had discovered the phenomenon of enantiomerism. The enantiomeric tartaric acid salts that Pasteur separated are physically identical in all respects except for their interaction with plane-polarized light. They have the same melting point, the same boiling point, the same solubilities, and the same spectroscopic properties. 

Although drawings provide a pictorial representation of stereochemistry, they are difficult to translate into words. Thus, a verbal method for indicating the three-dimensional arrangement of atoms, or configuration, at 

RULE 1 Look at the four atoms directly attached to the chirality center, and assign priorities in order of decreasing atomic number. The atom with highest atomic number is ranked first the atom with lowest atomic number is ranked fourth. 

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

The specification of the configuration of diastereomers is done by a direct extension of the sequence rule. Each chiral center is designated Rot Shy application of the sequence rule. The structures in Fig. 2.3 can serve as examples for study. 

For the specification of absolute configuration in other cases the sequence rule is now in general use, with its symbols JK, r, Jf, and P it is described in its simplest form in several recent textbooks and in detail in the original papers. ... 

Next, to ensure compatibility in process configuration several constraints must be satisfied. First, the inclusion conditions determine whether specific processes should be included in a configuration. Second, the precedence constraints that determine which processes are completed before the commencement of others must be clearly stipulated. These constraints, therefore, determine the sequence of processing, also known as process-flow. Finally, the execution-rules specify equipment needed. The process sequence together with the assignment of resources to process determine the estimated cycle time for completing the operation. 

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