Absolute configuration of chelate ring

Figure 2-6. The two enantiomeric forms of the chelate ring present in complexes of 1,2-diaminoet-hane. The labels 8 and X describe the absolute configuration of the chelate ring.

It was recognized quite early that the chelate rings of these ligands could not adopt a planar structure16,17K The more stable gauche conformation may present X or 5 helicity so that substituents fixed on the carbon chain can adopt two non-equivalent positions. If the absolute configuration of such a ligand is determined, as for example in R(—)propylenediamine, one of the two conformations becomes more stable. On... 

This result corresponds to the conformational analysis which predicts 24 as the most stable one. As already mentioned, it is possible to fix the absolute configuration of a given isomer by a suitable choice of substituents. A selection between different geometrical isomers — e.g. on the base of chelate ring size — seems to be less easy. It... 

Figure 1-18 Different ways of viewing the puckering of ethyl-enediamine chelate rings. The ab-S solute configurations A and S are defined. [Reproduced by permission from C. J. Hawkins, Absolute Configurations of Metal Complexes, Wiley, New York, 1971.]...

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