Pseudoasymmetry: a final twist?
The original definition of "pseudoasymmetry" conveyed the apparent paradox that a tetrahedral center with four different groups did not result in overall chirality. However, there are problems in applying the concept to cyclic systems that do not contain chirotopic centers. Pseudoasymmetry appears most appropriate to acyclic systems with chirotopic carbon centers, e.g. the meso trihydroxyglutaric acids. Analogous cyclic cases, e.g. the isomeric 1,4-dimethylcyclobutanes, are best treated as diastereomers, and may indeed be described by an interesting extension of the like-unlike notation. Remarkably, in several tri- and tetramethylcyclohexanes, CIP descriptors cannot be applied even to chirotopic centers, which can only be described by the modified l-u notation.
Chandrasekhar
Sosale
S
Department of Chemistry, Middle East Technical University, 06531 Ankara, Turkey. sosale@orgchem.iisc.ernet.in
D003503:Cyclobutanes / Q000737:chemistry; D005977:Glutarates / Q000737:chemistry; D009930:Organic Chemicals / Q000737:chemistry*; D013237:Stereoisomerism; D009626:Terminology as Topic
D003503:Cyclobutanes; D005977:Glutarates; D009930:Organic Chemicals