EXPERIMENTAL AND THEORETICAL-STUDY OF MONOSUBSTITUTED GUANIDINES BY VIBRATIONAL SPECTROSCOPY .1. STRUCTURE OF CYANOGUANIDINE

We have recorded and analysed IR absorption and Raman spectra of cyano guanidine C2N4H4 (CG) in different physical states (crystalline, solut ions and composition with porous glasses). Go-existence of two differe nt structural CG species: cyanoimine I and cyanoamine II with conjugat ed and isolated multiple bonds, respectively, is shown. The ratio of s tructure I to structure II can be varied using a porous glass techniqu e. Density functional calculations (B-LYP/6-31G) of the optimal struc ture and vibrational frequencies of CG confirm that cyanoimine and cya noamine co-exist. We suggest that the X-ray diffraction data showing e quivalent G-N and C=N bond lengths in the guanidine fragment is a cons equence of superposition of both tautomers that are present simultaneo usly in CG samples.