Stereoisomers, generation

NouJ79 Nourse, J. G. The configuration symmetry group and its application to stereoisomer generation, specification and enumeration. J. Am. Chem. Soc. lOl (1979) 1210-1216. ObeW67 Oberschelp, W. Kombinatorische Anzahlbestimmungen in Relationen. Math. Ann. 174 (1967) 53-58. 

The number of stereoisomers generated by a pentacoordinate center varies with... 

The diastereoisomers can be separated by GC on a nonchiral column because they have different retention times. However, the mass spectra of diastereoisomers are identical. As an example, in Figure 4.1.2 are shown four peaks that have identical mass spectra and are stereoisomers generated from the pyrolysis of poly(vinyI ethyl ether). Four diastereoisomers correspond to eight stereoisomers and consequently to a set of compounds with three chiral centers. 

The meso-(25, 35, 1R, 8R)-tetramethyl derivative (2) of S4 symmetry discussed in Figure 2 is one of seven possible stereoisomers generated by desymme-trization of the original symmetry inherent in the parent spiro [4.4] nonane framework, as shown by the projection formula in Figure 8. 

System for Elucidation of Structures of Organic Compounds (Esesoc) - Algorithm on Stereoisomer Generation. 

M. Contreras, J. Alvarez, D. Guajardo, and R. Rozas. Algorithm for exhaustive and nonredun-dant organic stereoisomer generation./. Chem. inf Model., 46 2288-2298, 2006. 

M. Razinger, K. Balasubramanian, M. Perdih, and M. Munk. Stereoisomer generation in computer-enhanced structure elucidation./. Chem. Inf Comput. Sci., 33 812-825,1993. 

Figure 3.1 Assignment of positions in pillar[5]- and pillar[6]arenes. Stereoisomers generated by rotation of constituent units are not included.

Although a compound of unknown structure is not fully characterized until both its constitution and absolute configuration are known, as currently practiced, the initial output of structure generation is the set of compatible constitutional isomers. Stereoisomer generation and assignment of configuration follow at a later stage. 

Initially, all stereocenters and their type (true or para) are identified. Each of the n stereocenters is then assumed to be a true stereocenter different from every other stereocenter. Since a stereocenter can only have one of two configurations (e.g., R or S), a compound with n different stereocenters will lead to a set of 2" different parity combinations, i.e, stereoisomers, the configuration of each of which can be expressed as a stereoparity (binary) vector of n elements. If the compound actually possesses n different stereocenters, stereoisomer generation is complete. If, on the other hand, the presence of topologically equivalent true stereocenters and/or para stereocenters has been identified, the number of stereoisomers will be less than 2". In operational terms, that means that redundancies exist in the set of 2" stereoparity vectors. The objective in this approach is to identify and remove those redundancies. The automorphism group of such a compound is the key to revealing equivalence among the stereoparity vectors. 

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