Sequence rule,

Groups attached to the chiral centre are given an order of priority according to the sequence rules. For an enantiomeric carbon compound the group of lowest priority is... 

Absolute Stereochemistry Absolute stereochemical assignment of each stereocenter (R vs S) Cahn-Ingold-Prelog Convention (sequence rules)... 

With the lowest ranked group (hydrogen) directed away from us we see that the order of decreasing sequence rule precedence is clockwise The absolute configuration is R... 

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... 

When the sequence rules permit alternatives, preference for lower-numbered locants and for inclusion in the principal chain is allotted as follows in the order stated Z over E groups and cis over trans cyclic groups. If a choice is still not attained, then the lower-numbered locant for such a preferred... 

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). 

Diastereomers include all stereoisomers that are not related as an object and its mirror image. Consider the four structures in Fig. 2.3. These structures represent fee four stereoisomers of 2,3,4-trihydroxybutanal. The configurations of C-2 and C-3 are indicated. Each stereogenic center is designated J or 5 by application of the sequence rule. Each of the four structures is stereoisomeric wife respect to any of fee others. The 2R R and 25,35 isomers are enantiomeric, as are fee 2R, iS and 25,3J pair. The 21 ,35 isomer is diastereomeric wife fee 25,35 and 2R,3R isomers because they are stereoisomers but not enantiomers. Any given structure can have only one enantiomer. All other stereoisomers of feat molecule are diastereomeric. The relative configuration of diastereomeric molecules is fiequently specified using fee terms syn and anti. The molecules are represented as extended chains. Diastereomers wife substituents on the same side of the extended chain are syn stereoisomers, whereas those wife substituents on opposite sides are anti stereoisomers. 

Scheme 2.8. Stereoisomeric Alkenes and Related Molecules with the Double-Bond Geometry Named According to the Sequence Rule...

The enzyme-catalyzed interconversion of acetaldehyde and ethanol serves to illustrate a second important feature of prochiral relationships, that ofprochiral faces. Addition of a fourth ligand, different from the three already present, to the carbonyl carbon of acetaldehyde will produce a chiral molecule. The original molecule presents to the approaching reagent two faces which bear a mirror-image relationship to one another and are therefore enantiotopic. The two faces may be classified as re (from rectus) or si (from sinister), according to the sequence rule. If the substituents viewed from a particular face appear clockwise in order of decreasing priority, then that face is re if coimter-clockwise, then si. The re and si faces of acetaldehyde are shown below. 

Using the sequence rule, specify the configuration at each stereogenic center in the following molecules ... 

Assign configurations, using the sequence rule, to each chiral center of the stereo-isomeric isocitric acids and alloisocitric acids ... 

Despite being notoriously difficult to analyze formally, the behavior of general CA rules is nonetheless often amenable to an almost complete mathematical characterization. In this section we look at a simple method that exploits the properties of certain implicit deterministic structures of elementary one-dimensional rules to help determine the existence of periodic temporal sequences, rule inverses and homogeneous states. Additional details appear in [jen86a] and[jen86b]. 

Called the Cnlm-Ingolrf-Prelog rules after the chemists who proposed them, the sequence rules are as follows ... 

Taking all the sequence rules into account, we can assign the configurations shown in the following examples. Work through each one to convince yourself that the assignments are correct. 

The left-hand carbon has -H and -CH3 substituents, of which -CH3 receives higher priority by sequence rule 1. The right-hand carbon has -CH(CH3)2 and -CH2OH substituents, which are equivalent by rule 1. By rule 2, however, -CH2OH receives higher priority than The substituent -CHbOH has an oxygen as... 

Rank the following sets of substituents in order of priority according to the Cahn-Ingold-Prelog sequence rules ... 

Look at (-)-laclic acid in Figure 9.8 for an example of how to assign configuration. Sequence rule 1 says that —OH has priority 1 and -H has priority 4, but it doesn t allow us to distinguish between -CH3 ancl -CCbH because... 

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