Chelate ring conformational equilibria

There are practically no quantitative measurements concerning the equilibrium la lb. Dwyer and coworkers studied the correlation between chelate ring conformation and complex configuration in a series of ethylenediaminepropylenediamin-cobalt(III) complexes. From the results, they conclude that the methyl group of propylenediamine is always in an equatorial position25,26). 

Over the past twenty years the conformations and steric effects in chelate ring systems have been examined in considerable detail. Structural studies along with equilibrium measurements, some kinetic studies and conformational analyses have given us a better insight into the steric interactions within the chelates and between the chelates (1). For five membered chelates such as coordinated 1,2 diaminopropane... 

Evidence very recently presented by O Farrell ei ah [3J indicates that the preferred conformation (XIII) of 2 hydroxy-5,6,7,8-tetra-hydro- 1-acetonaphthone is that which is unfavourable for chelation. However, this is not necessarily inconsistent with our views. Certainly XIII is in equilibrium with that conformation (XIV) which is favourable for chelation. Our argument merely postulates that chelation in a conformation like XIV is favoured by the bulk of the methylene group in the alicyclic ring. 

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