Khodabakhsh Niknam

All 66 conformers of guanylurea were optimized and frequency calculations were performed at M06-2X/6-311 G(d,p) level of theory. Theses conformers were categorized into five tautomers, and the most stable conformer of each tautomer were found. Geometrical paramaters indicated that these tautomers have almost planar structure. Complete stepwise tautomerism were studied through both intramolecular proton transfer routs and internal rotations. Results indicated that the proton transfer routs involving four-membered heterocyclic structures were ratedetermining steps. Also, intramolecular proton movement having six-membered transition state structures had very low energy barrier comparable to the transition states of internal rotation routs. Differentiation of studied tautomers could easily be done through their FT-IR spectra in the range of 3200 to 3900 cm-1 by comparing absorption bands and intensity of peaks. Solventimplicit effects on the stability of tautomers were also studied through re-optimization and frequency calculation in four solvents. Water, DMSO, acetone and toluene had stabilization effect on all considered tautomers, but the order of stabilization effect was as follows: water > DMSO > acetone > toluene