Stereotopic Relationships of Groups in Molecules

Many of the ideas espoused in this and the next section are due to the work of Mislow 

Homotopic Groups Not distinguishable under any conditions, chiral or achiral. To have homotopic groups, a molecule must have a finite axis of rotation. Thus the only molecules which cannot have homotopic groups are those whose point groups are Ci, CS) Q, and CCXJV. 

Enantiotopic Groups The same in all scalar properties, distinguishable only under chiral conditions. 

Constitutionally Heterotopic and Diastereotopic Groups Differ in all scalar properties and are distinguishable under any conditions, chiral or achiral. Asymmetric molecules cannot contain homotopic or enantiotopic groups, only diastereotopic or constitutionally heterotopic groups. 

Groups may be compared by internal comparison (groups in the same molecule) or by external comparison (groups in different molecules). 

Many of the ideas espoused in this and the next section are due to the work of Mislow [29]. For an alternative discussion of the concepts introduced in this section, see reference 30. The reader is also directed to excellent texts by Juaristi [31] and by Eliel and Wilen [32], 

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