The hydrogen bonds in three tautomeric forms of trans-N,N-bis-(R-salicylidene)- 1,2-cyclohexanediamine (R = H, 5-NO2, 4,6-di-OCH3 and 3,5-di-Cl) have been studied by DFT calculations and topology of density charge function according to Bader’s AIM theory. Comparison of the CP values at the H…N and H…O bond critical points (BCP) for the compounds studied has revealed the effect of substituents on the hydrogen bonds strengths in the two chelate rings of trans-N,N-bis-(R-salicylidene)-1,2-cyclohexanediamines.
Results of UV-visible spectroscopic studies on thermodynamic parameters of the intramolecular proton transfer equilibrium in N-(R-salicylidene)-alkylamines in solution are presented. The estimated DeltaHPT values in CH2Cl2 solution are within the range –5.2 to –13.9 kJ/mol. DeltaSPT values are negative: from –28 to –48 J/molK. The obtained results demonstrate the influence of the acidity of the phenolic group as well as charge delocalization on the position of the proton transfer equilibrium.
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