E,Z Notation

Exercise 19-9 Designate the configuration at each asymmetric carbon in each of the following projection or stereo formulas by both the d,l and fl.S systems  

Exercise 19-10 Draw saw-horse and projection formulas for each of the following compounds, and designate whether the particular enantiomer is erythro, threo, cis, or trans  

The configuration about double bonds is undoubtedly best specified by the cis-trans notation when there is no ambiguity involved. Unfortunately, many compounds cannot be described adequately by the cis-trans system. Consider, for example, configurational isomers of l-fluoro-l-chloro-2-bromo-2-iodo- 

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  

An order of precedence is established for the two atoms or groups attached to each end of the double bond according to the sequence rules of Section 19-6. When these rules are applied to l-fluoro-l-chloro-2-bromo-2-iodoethene, the priority sequence is  

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Double bonds m the mam chain are signaled by the ending enow acid and their position IS designated by a numerical prefix Entries 6 and 7 are representative carboxylic acids that contain double bonds Double bond stereochemistry is specified by using either the cis-trans or the E-Z notation... 

Using E-Z notation (3E,5E,llE)-l,3,5,ll-Tridecatetraen-7,9-diyne The parent alkane of this hydrocarbon is tridecane. 

Syn isomer In the case of trisubstituted C=N compounds, i.e. XYC=NZ, if Z is the same as one of the substituents on the carbon, i.e. X or Y, then the syn isomer is the one that has the two identical substituents on the same side if they are on opposite sides, then it is the anti isomer. If all three substituents are different then the E/Z notation must be used. 

Trans A stereochemical term used to indicate that the two groups under consideration are attached one at each end of a double bond and are on opposite sides of the double bond, rather than on the same side as in the cis isomer. To characterise more fully a system in which there are more than two different groups, then the CIP rules need to be invoked, and the E/Z notation used instead. 

The (E) (Z) notation is adopted for the definition of the geometries of silylketene acetals as well as metal enolates. As a consequence, silylation of ( )-lithium ester etiolates leads to (Z)-silylketene acetals. 

E—Z notation for alkenes (Section 5.4) System for specifying double-bond configuration that is an alternative to cis—tons... 

Stereochemistry is systematically described by the E-Z notation. Here, the double bond between C-6 and C-7 in octenoic acid has the Z configuration the higher ranked substituents are on the same side. 

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