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Updated: May 9, 2026

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Published on: November 23, 2016
The zwitterionic structure of 2-hydroxy-4-[(2-hydroxybenzylidene)amino]benzoic acid
Anderson A B C Júnior1, Gustavo S G De Carvalho, Lippy F Marques
1Department of Chemistry, Federal University of Juiz de Fora, Juiz de Fora, Minas Gerais 36036-900, Brazil.
Abstract:
The title compound, C₁₄H₁₁NO₄, exists in the solid phase in the zwitterionic form, 2-{[(4-carboxy-3-hydroxyphenyl)iminiumyl]methyl}phenolate, with the H atom from the phenol group on the 2-hydroxybenzylidene ring transferred to the imine N atom, resulting in a strong intramolecular N-H∙∙∙O hydrogen bond between the iminium H atom and the phenolate O atom, forming a six-membered hydrogen-bonded ring. In addition, there is an intramolecular O-H∙∙∙O hydrogen bond between the carboxylic acid group and the adjacent hydroxy group of the other ring, and an intermolecular C-H∙∙∙O contact involving the phenol group and the C-H group adjacent to the imine bond, connecting the molecules into a two-dimensional network in the (103) plane. π-π stacking interactions result in a three-dimensional network. This study is important because it provides crystallographic evidence, supported by IR data, for the iminium zwitterionic form of Schiff bases.
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