Intramolecular Hydrogen Bonding and Tautomerism in Schiff Bases: Synthesis, Spectroscopic and Theoretical Studies of N-(2,2'-Methylenebis(4-methoxyphenyl)salicylidene and N-(2,2'-Methylenebis(4-methoxyphenyl)-2-oxonaphthalidene-methylamine
作者:Hakan Dal
DOI:10.14233/ajchem.2014.16725
日期:——
The new Schiff bases (4 and 5) were synthesized respectively from the reaction of 2,2-methylenebis(4-aminomethoxybenzene) (3) with salicylaldehyde and 2-hydroxy-1-naphthaldehyde. The products have been characterized by elemental analysis, FTIR, UV-visible and NMR techniques. The tautomeric equilibria of 2-hydroxy Schiff bases were investigated in polar, non-polar, acidic and basic media by using UV-visible absorption spectra. Compound 4 is in, predominantly, phenol-imine (O-H···N) form, whereas compound (5) is in tautomeric equilibria (phenol-imine, O-H···N and keto-amine, O···H-N forms) in polar and non-polar solvents, as supported by 1H NMR and UV-visible data. All of the NMR assignments were made using 1H, 13C NMR and aided by 2D COSY, NOESY, HETCOR and HMBC heteronuclear correlation techniques. In addititon, theoretical calculations have been carried out PM6 methods in the MOPAC2009 and Marvinbeans-5_3_01-windows programs. The heat of formation (DHf), enthalpy (DH), entropy (DS) Gibbs free energy (DG), conformations and tautomers of the synthesized compounds are estimated by using MOPAC2009 (PM6) program.
新的希夫碱(4 和 5)分别由 2,2-亚甲基双(4-氨基甲氧基苯)(3)与水杨醛和 2-羟基-1-萘甲醛反应合成。通过元素分析、傅立叶变换红外光谱、紫外可见光和核磁共振技术对产物进行了表征。利用紫外可见吸收光谱研究了 2-羟基希夫碱在极性、非极性、酸性和碱性介质中的同分异构平衡。化合物 4 主要以酚-亚胺(O-H--N)形式存在,而化合物 (5) 则在极性和非极性溶剂中处于同分异构体平衡状态(酚-亚胺、O-H--N 和酮-胺、O-H-N 形式),这一点得到了 1H NMR 和紫外可见光数据的支持。所有的核磁共振分析都是通过 1H、13C NMR 以及二维 COSY、NOESY、HETCOR 和 HMBC 异核相关技术进行的。此外,还使用 MOPAC2009 和 Marvinbeans-5_3_01-windows 程序中的 PM6 方法进行了理论计算。使用 MOPAC2009 (PM6) 程序估算了合成化合物的形成热(DHf)、焓(DH)、熵(DS)、吉布斯自由能(DG)、构象和同系物。