Experimental and theoretical study of monosubstituted guanidines by vibrational spectroscopy Part 1.—Structure of cyanoguanidine

We have recorded and analysed IR absorption and Raman spectra of cyanoguanidine C 2 N 4 H 4 (CG) in different physical states (crystalline, solutions and composition with porous glasses). Co-existence of two different structural CG species: cyanoimine I and cyanoamine II with conjugated and isolated multiple bonds, respectively, is shown. The ratio of structure I to structure II can be varied using a porous glass technique. Density functional calculations (B-LYP/6-31G*) of the optimal structure and vibrational frequencies of CG confirm that cyanoimine and cyanoamine co-exist. We suggest that the X-ray diffraction data showing equivalent C–N and CN bond lengths in the guanidine fragment is a consequence of superposition of both tautomers that are present simultaneously in CG samples.