2015. 56, 5 UDC 541.6:541.67 INTRAMOLECULAR-PROTON TRANSFER, EXPERIMENTAL AND THEORETICAL CHARACTERIZATION OF 3,3-DIHYDROXY-4,4-[4,4-DIPHENYLMETHANEBIS (NITRILOMETHYLIDYNE)]-BIS-PHENOL H. Eshtiagh-Hosseini1, S.A. Beyramabadi2, M. Mirzaei1, A. Morsali2, M.A. Naseri3, H. Chegini2, M. Elahi2 3Department of Chemistry, Faculty of Science, Birjand University, Birjand, Iran Received January, 13, 2014 1Department of Chemistry, Ferdowsi University of Mashhad, Mashhad, Iran 2Department of Chemistry, Mashhad branch, Islamic Azad University, Mashhad, Iran E-mail: beiramabadi6285@mshdiau.ac.ir Revised — July, 11, 2014 A newly synthesized Schiff base 3,3-dihydroxy-4,4-[4,4-diphenylmethanebis(nitrilomethylidyne)]-bis-phenol is characterized experimentally. <...> Also, the geometry optimization for the tautomers, tautomerism and assignment of the IR bands and NMR chemical shifts of the Schiff base were performed using the DFT method. <...> Geometries of four possible tautomers are fully optimized. <...> None of them has a planar structure, but each of the benzene rings is in a separate plane. <...> In the most stable tautomer L1, the phenolic protons are engaged in the intramolecular-hydrogen bond with the azomethine nitrogen atoms. <...> Tautomerization of L1 can occur in two different pathways which are computationally studied using DFT and the Atoms In Molecules (AIM) analysis. <...> Both pathways have the same barrier energy. <...> In continuation of our previous works on the chemistry of Schiff bases [12—18 ], herein we report the synthesis, experimental and theoretical investigation of a new Schiff-base (3,3-dihydroxy4,4-[4,4-diphenylmethanebis(nitrilomethylidyne)]-bis-phenol), which is named as L. By comparing the theoretical and experimental results, the validity of the optimized structures has been evaluated. <...> Elemental analysis (C, H, N) was performed on a Heraeus CHN-O-Rapid elemental analyzer. <...> A solution of 1.32 g (6.66 mmol) of 4-(4aminobenzyl)benzenamine and 1.88 g (13.61 mmol) of dihydroxybenzaldehyde in toluene (150 ml) was refluxed under vigorous stirring with a Dean-Stark for 3 h. <...> COMPUTATIONAL DETAILS All calculations have been performed using density functional theory with the B3LYP functional [ 19 ] as implemented in the Gaussian 03 program package [ 20 ]. <...> The optimized geometries were confirmed to have no imaginary frequency of the Hessian, which <...>