Prostereoisomerism and Asymmetric Synthesis

26 This criterion should be applied to the conformation of highest symmetry. It does not apply to cases where the A and B nuclei are themselves symmetry equivalent, such as C1CH2CH2C1 or p-dichlorobenzene. 

Another, important, application of the use of isotopic labeling to decide which of two stereoheterotopic ligands is involved in a classical chemical reaction is in the work of J. Sicher and his school concerning the mechanism of onium ion elimination 110 . As the result of extensive studies, it was concluded (Fig. 53) that elimi- 

By far the most extensive applications of this technique, however — i.e. of ascertaining which of two stereoheterotopic ligands or faces is implicated in a given reaction — have been in enzyme chemistry and the next section will deal with this topic. 

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