syntheses and structural studies of schiff bases involving hydrogen bonds合成和结构的研究涉及氢键的希夫碱.pdf

Molecules 2006, 11, 453-463 molecules ISSN 1420-3049 Full Paper Syntheses and Structural Studies of Schiff Bases Involving Hydrogen Bonds Almudena Perona 1,*, Dionisia Sanz 1,*, Rosa M. Claramunt 1,† and José Elguero 2 1 Departamento de Química Orgánica y Bio-Orgánica, Facultad de Ciencias, UNED, Senda del Rey 9, E-28040 Madrid, Spain; †e-mail: rclaramunt@ccia.uned.es 2 Instituto de Química Médica (CSIC), Centro de Química Orgánica Manuel Lora Tamayo, Juan de la Cierva 3, E-28006 Madrid, Spain; e-mail: iqmbe17@iqm.csic.es * Authors to whom correspondence should be addressed; Fax: (+34) 913988372; e-mail: aperona@bec.uned.es; dsanz@ccia.uned.es Received: 7 June 2006; in revised form: 20 June 2006 / Accepted: 20 June 2006 / Published: 21 June 2006 Abstract: New Schiff bases have been prepared by reacting 3-hydroxy-4-pyridine- carboxaldehyde with various amines. NMR spectroscopic methods provided clear evidence that the Schiff bases exist in the solid state and in solution as hydroxyimino tautomers with the E-configuration. A study of the stabilities of the tautomeric forms and the different conformers has been carried out using density functional calculations at the B3LYP/6-31G** level. Keywords: Schiff bases, Tautomerism, Hydrogen bonds, NMR spectroscopy, Density functional calculations. Introduction It is well established that hydrogen bonds (HB) and proton transfer (PT) reactions play a crucial role in many areas of physical, chemical and biological phenomena. It appears