The Crystal Structure of Dicyandiamide

Abstract

Several different structures have been proposed for the dimer of cyanamide but no absolutely conclusive evidence has ever been given for any one of them. In past years many people have preferred the cyanoguanidinel structure I. But even fairly recently arguments have been advanced in favor of the cyclic structure II. The closely related alternatives III and IV, which differ from I or II only in the disposition of hydrogens and double bonds, also have been proposed. I have made an X-ray examination of crystalline dicyandiamide for the purpose of resolving this long-standing controversy, with the results reported below.

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