Schematic Representation of the Single TR

It is convenient to introduce the TR mechanism by giving a schematic representation of it as shown in Fig. 5. However, it should be emphasized that the actual TR phenomenon is different, and corresponds to certain motions of the atoms which will be described in detail in the next Section. 

On the other hand, the BPR process corresponds to a subclass of the class Ci, involving the alternating permutations (ae a e ). Any given 

It is self-evident that an overall 60° and the reverse overall 300° internal rotations of a pair of ligands relative to a trio accomplish exactly the same result. The actual TR-phenomenon that accomplishes the isomerization (1 4) (2 5) (1 2) in Fig. 5 corresponds to a clockwise 60° 

In an idealized situation in which the five ligands are equivalent and in which there is no intermolecular exchange of angular momentum, the actual TR-phenomenon that effects the isomerization (1 4) (2 5) - (1 2) of Fig. 5 corresponds to the clockwise 36° rotation of the pair vs. the counterclockwise 24° rotation of the trio with conservation of internal angular momentum. The conservation of intramolecular angular momentum is not a necessary condition for TR, but it should be pointed out that only TR and BPR, among all the formal mechanisms discussed above, possess this capability. In general, to describe the actual TR in the isomerization (1 4) (2 5) - (1 2) of Fig. 5 all that needs to be said is that there is a clockwise overall 60° internal rotation of the pair relative to the trio. 

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