Tautomerism in Alicyclic Lactams 2-Pyrrolidinone

Here we explore a long but fruitful isodesmic approach that leads to a possible way of estimating iCj for 8, the five-membered ring equivalent to 5. 

The equilibria are written throughout so as to replace a six- by a five-membered ring. It will be seen that, in all cases, the effect is to replace a decrease in stability with an increase. The overall result is remarkably similar in all three cases, with AlogiC 1.16 0.07. The most obvious factor at work is that, while C=C with its 

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