INTRAMOLECULAR HYDROGEN-BONDING AND TAUTOMERISM IN SCHIFF-BASES - PART 1 - STRUCTURE OF 1,8-DI[N-2-OXYPHENYL-SALICYLIDENE]-3,6-DIOXAOCTANE

1,8-Di[N-2-oxyphenyl-salicylidene]-3,6-dioxaoctane (1) and -2-oxo-1-na phthylidenemethylamino]-3,6-dioxaoctane (2) are obtained from the reac tion of triethylene glycol bis(2-aminophenyl ether) with salicylaldehy de and 2-hydroxy-1-naphthaldehyde. Compounds (1) and (2) have been cha racterized by elemental analysis, IR, H-1-NMR and UV-visible technique s and the structure of compound (1) has been examined crystallographic ally. The UV-visible spectra of 2-hydroxy Schiff bases are studied in different solvents and acidic media. Compound (2) is in tautomeric equ ilibria (phenolimine, O-H...N reversible arrow keto-amine, O...H-N for ms) in polar and non-polar solvents. These tautomers are not observed in polar and non-polar solvents for (1) as supported by H-1-NMR and UV -visible data. The keto-amine form is observed in acidic solutions of chloroform and benzene, but it is not observed in solutions DMSO and E tOH for compounds (1) and (2). Compound (1) is in the form of phenol-i mine in solid state and a crystallographically centrosymmetric multide ntate Schiff base ligand, containing two imine nitrogen, two hydroxy a nd four etheric O atoms. There is a strong intramolecular [O-H...N = 1 .488(3)Angstrom] hydrogen bond. The C = N imine bond and C-N-C bond an gle are 1.270(3)Angstrom and 123.5(2)degrees. It crystallizes in the m onoclinic space group P2(1)/n with a = 6.301(1), b = 13.624(1), c = 16 .189(1)Angstrom, beta = 100.28(1)degrees, V = 1367.4(3)Angstrom(3), Z = 2 and D-x = 1.313 g cm(-3). (C) 1998 Elsevier Science B.V.