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In most of the books, the reason of macrocyclic effect is given that It occurs due to preorganised structure of macro-cyclic ligand.  But a proper explanation of these two particular examples isn't given anywhere (even in the book from I've read it).

I've come up with the following explanation - 

Cyclam has just a proper size for bonding, therefore it is stable due to its Bond Enthalpy, But it's a big molecule so It should have more Degree of freedom. For a proper bonding, it has to be in some particular conformation out of many other conformations. So it is an entropically disfavored molecule.

But in case of Cyclen, Its ring is small so its bonding isn't that good as compared to cyclam but since it is a smaller molecule so there should be less no. of possible conformation, So statistically achieving that particular conformation isn't that hard for Cyclen. 

I don't know why? But it's not satisfying me, am I making some mistake (overlooking something important)? Or Is it correct?

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  • $\begingroup$ Have you find an answer? I am also having the same question. $\endgroup$
    – ado sar
    Nov 11, 2020 at 18:22

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