specific features of intramolecular proton transfer reaction in schiff bases分子内质子转移反应的具体特点希夫碱.pdf

Int. J. Mol. Sci. 2003, 4, 434-444 International Journal of Molecular Sciences ISSN 1422-0067 © 2003 by MDPI /ijms/ Specific Features of Intramolecular Proton Transfer Reaction in Schiff Bases Aleksander Koll Faculty of Chemistry, University of Wrocław, 14 F. Joliot-Curie, 50-383 Wrocław, Poland E-mail: akoll@wchuwr.chem.uni.wroc.pl Received: 3 April 2003 / Accepted: 9 April 2003 / Published: 25 June 2003 Abstract: The differences between the intramolecular proton transfer in Mannich and Schiff bases are discussed. The tautomeric forms being in equilibrium in both types of molecules are seriously different. In Mannich bases there are in equilibrium the forms of phenols and phenolates. In Schiff bases each of tautomers is strongly influenced by resonance between zwitterionic and keto structures. Despite the common opinion that the proton transfer forms in compounds with internal π-electronic coupling are mainly keto forms it is shown in this work, that in Schiff bases the content of keto structure is slightly less than zwitterionic one. Almost equal participation of both forms leads to effective resonance between them and stabilization of intramolecular hydrogen bond in this way. Keywords: intramolecular proton transfer, Schiff bases, hydrogen bond. Introduction Intramolecular hydrogen bonds are often applied model systems in the study of the proton transfer reaction. An advantage of using such specific systems