• 主题
高级搜索  >
历史搜索 清空历史
首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Proton Transfer Equilibria in Schiff Bases with Steric Repulsion
【24h】

Proton Transfer Equilibria in Schiff Bases with Steric Repulsion

机译：带有立体排斥的席夫碱中的质子转移平衡

获取原文
获取原文并翻译 | 示例
           
页面导航
  • 摘要
  • 著录项
  • 相似文献
  • 相关主题

摘要

The proton transfer equilibria in CH_2Cl_2 solutions of 2-(α-(N-methylimino)ethyl)phenol (1), 2-(α-(N-methylimino)ethyl)-4,6-dichlorophenol (2) and 2-(α-(N-propylimino)ethyl)-4,6-dichlorophenol (3) are studied by UV-vis, 1H NMR, and FT-IR spectra as a function of temperature. Thermodynamic parameters of the proton transfer reaction have been determined. It has been demonstrated that introducing of the methyl substituent into the C-C(H)=N moiety of the Schiff bases alters the tautomeric equilibrium in favor of the proton transfer forms in comparison with Schiff bases deprived of such substituent and related Mannich bases. Solvatochromy of electronic absorption in Schiff bases is evidence that the proton transfer state is neither zwitterionic nor orthoquinoid in their character but has to be taken as a resonance hybrid of these forms. According to this, a scheme of proton transfer equilibria specific for Schiff bases is proposed, which is in agreement with numerous structural evidences. The B3LYP/6-31G(d,p) frequency calculations performed for both the molecular and proton transfer forms precisely reproduce the experimental spectra measured as a function of temperature. The calculations show that the (C=N) band assignment, widely discussed in the literature, is ambiguous because of the strong dependence of normal coordinates content on the character and conformation of particular forms of molecules. The calculations definitely show that the protonation of the C=N-R group decreases the force constants of the C=N bonds, in spite of numerous opposite suggestions in the literature.
机译：2-（α-（N-甲基亚氨基）乙基）苯酚（1），2-（α-（N-甲基亚氨基）乙基）-4,6-二氯苯酚（2）和2-（-）在CH_2Cl_2溶液中的质子转移平衡通过UV-vis，1H NMR和FT-IR光谱研究了α-（N-丙基亚氨基）乙基）-4,6-二氯苯酚（3）与温度的关系。已经确定了质子转移反应的热力学参数。已经证明，与缺乏所述取代基和相关曼尼希碱的席夫碱相比，将甲基取代基引入席夫碱的C-C（H）＝ N部分改变了互变异构平衡，有利于质子转移形式。 Schiff碱中电子吸收的溶剂化色度证明，质子转移态的特性既不是两性离子型也不是邻醌型，而必须被视为这些形式的共振混合体。据此，提出了一种针对席夫碱的质子转移平衡方案，该方案与众多结构证据相吻合。针对分子和质子转移形式执行的B3LYP / 6-31G（d，p）频率计算精确地再现了作为温度函数测得的实验光谱。计算表明，在文献中广泛讨论的（C = N）带分配是模棱两可的，这是因为法向坐标含量强烈依赖于特定形式分子的特征和构象。尽管在文献中提出了许多相反的建议，但这些计算无疑表明，C = N-R基团的质子化降低了C = N键的力常数。

著录项

相似文献

  • 外文文献
  • 中文文献
  • 专利
获取原文

客服邮箱：kefu@zhangqiaokeyan.com

京公网安备：11010802029741号 ICP备案号：京ICP备15016152号-6 六维联合信息科技 (北京) 有限公司©版权所有

  • 客服微信

  • 服务号