Multinuclear magnetic resonance and theoretical calculations in the study of structure and tautomerism of some 2-amino-N'-(aryl)-benzamidines.
1H, 13C and 15N NMR spectra of eight 2-amino-N'-(aryl)-benzamidines and of the parent compound were recorded, and unequivocal chemical shift assignments through the use of COSY, 1H-J resolved, HETCOR and COLOC sequences were performed. 1H and 13C chemical shifts for the nuclei of the benzamidine aromatic ring were not affected by the substituents present at N'-phenyl group, while the substituent effects in the chemical shifts of the same nuclei of N'-phenyl ring were very similar to the ones reported for the corresponding monosubstituted benzenes, indicating that there is no interaction between the two aromatic rings. 15N NMR spectra (DEPT sequence) show just two hydrogenated nitrogen atoms, which confirm that the amino form is the most stable tautomer, but the observation of a sharp signal and two broad signals (15N decoupled spectra), and the corresponding broad signal for the =C-NH(2) protons (in the 1H spectra), indicates the occurrence of tautomerism between the amino and imino forms, observable for some of the studied benzamidines. Theoretical calculations lead to the conclusion that these compounds occur mostly as the amino tautomer with Z configuration, which is stabilized by hydrogen bonding.
Suwinski
J
J
Institute of Organic Chemistry and Technology, The Silesian Technical University, Gliwice 44-100, Poland.
Szczepankiewicz
W
W
Basso
E A
EA
Tormena
C F
CF
Freitas
M P
MP
Rittner
R
R
D001550:Benzamidines / Q000737:chemistry*; D002151:Calorimetry; D009682:Magnetic Resonance Spectroscopy / Q000379:methods; D008962:Models, Theoretical; D008968:Molecular Conformation
D001550:Benzamidines