Nonstereogenic atom

P. Beak, Determinations of Transition-State Geometries by the Endocyclic Restriction Test Mechanism of Substitution at Nonstereogenic Atoms, Acc. Chem. Res. 1992, 25, 215-222 P. Beak, Mechanisms of Reactions at Nonstereogenic Heteroatoms Evaluation of Reaction Geometries by the Endocyclic Restriction Test, PureAppl. Chem. 1993, 65, 611-615. 

This molecule, the most symmetrical of the three, is achiral. The central carbon atom is completely nonstereogenic. Both planes are planes of symmetry and the hydrogens are homotopic. They are chemically and magnetically equivalent. 

Mislow and Siegel gave as an example the set of isomers of 2,3,4-trihydroxyglutaric acid, 107-110. Neither 107 nor 108 is chiral because both are meso structures. In both structures, C3 has been labeled "undoubtedly an asymmetric carbon atom." ° According to Mislow and Siegel, however, C3 is stereogenic and achirotopic in 107 and 108. On the other hand, C3 is nonstereogenic and chirotopic in compounds 109 and 110. 

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