Structure of epsilon-Caprolactam

A molecule of epsilon-caprolactam. Take a good look at this molecule and ask yourself whether the conformations are what you would expect them to be. Basically, the form of the 7-ring is that expected for cycloheptane and all the C-C-C-C units are gauche. Most bonds, except for one, are largely staggered. But, yes, the amide linkage is very strange! Usually amides like to be such that the NHCO atoms are in the same plane. In epsilon-caprolactam, the ring strain seems to prevent that best amide conformation from being realized. Even if the effect is overdone by the particular Molecular Modeling Program employed here, the effect also can be seen in more accurate structures.


Figure. A molecular model of epsilon-caprolactam.