Nomenclature substituents, arrangement

The a-carbon of all amino acids, with the exception of glycine, has four different substituent groups and is therefore an asymmetric carbon atom. Such an atom can exist in two different spatial arrangements which are mirror images of each other. These structural forms of molecules are known as stereoisomers and the common notation of D and L forms is used, a nomenclature that refers to their absolute spatial configuration when compared with that of glyceraldehyde (Figure 10.4). 

The stereochemistry of the cycloadducts in intramolecular Diels-Alder reactions depends upon the different geometry of the possible transition states 37—40 whose nomenclature can be explained as follows The orientation with the chain connecting the diene and dienophile lying under or above the diene is called endo. The opposite means exo. E and Z mark the geometry of the diene double bond which is connected with the chain. Syn and anti describe the arrangement of the hydrogen atoms (or substituents) at the prestereogenic centers which are involved in the C-C bond formation.12... 

The fundamental principles of CAS nomenclature and the systematic CA Index Names will be briefly explained using two examples. Index Names are primarily arranged under the heading of the fiinctional parent compound, followed by the substituents in alphabetical order, the name modification to the parent compound and, finally, the stereo chemical descriptor, when necessary. The parent compound, characterized by its functional group, of the substance... 

To differentiate two enantiomers, we need a system of nomenclature that indicates the arrangement or configuration of the four groups about the chiral center. Such a system was developed by three chemists, R. S. Cahn, C. Ingold, and V. Prelog. The first step is to rank the four substituents in order of decreasing priority. The rules for assigning priorities will be described shortly. 

The E, Z system is a system of nomenclature used to describe the arrangement of substituent groups bond to the C atoms of a carbon-carbon double bond. 

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