Proton transfer equilibrium in the intramolecular hydrogen bridge in sterically hindered Schiff bases

Six Schiff bases (4-chloro-2-(1-ethyliniino-ethyl)-5-methyl-phenol (1), 2,4-dichloro-6-(1-ethylamino-ethylidene)-cyclohexa-2,4-dienone (II), 4-chloro-2-nitro-6-(1-ethylamino-ethylidene)-cyclohexa-2,4-dienone (III), 2-nitro-4-methyl-6-(l-ethylamino-ethylidene)-cyclohexa-2,4-dienone (IV), 2-(1-phenylimino-iso-propyl)-phenol (V) and 4-chloro-2-(1-phenyliminoethyl)-5-methyl-phenol (VI)) were synthesised with replacement of the H atom in the C-C(H)=N group by either methyl, or phenyl substituent. The data were collected at 293 K temperature. Additionally in order to study the temperature influence on proton transfer two crystal structures were obtained at 100 K temperature. The influence of different substitution in phenol ring on the position of hydrogen in hydrogen bridge was discussed. (C) 2002 Elsevier Science B.V. All rights reserved.