13C NMR relaxation time measurements of macrocyclic ether complexes. The association of benzo[18]crown-6 with NaClO4·H2O in acetonitrile

✍ Scribed by Çakıl Erk; Manfred D Zeidler

• Publisher: Elsevier Science
• Year: 1999
• Tongue: English
• Weight: 406 KB
• Volume: 79
• Category: Article
• ISSN: 0167-7322
• DOI: 10.1016/s0167-7322(98)00099-3

✦ Synopsis

Association constants for the complex Na'/benzo [18]crown-6 in acetonitrile solution were determined from t3C-NMR relaxation time measurements at different temperatures. The dipolar contributions to relaxation were separated by nuclear Overhauser enhancement measurements. The contributions are split into parts originating from uncomplexed and from complexed macrocycles assuming the 1:1 complex formation between Na t and crown ether and by measuring solutions of different concentrations. The measured data were analysed to yield the respective relaxation times and the association constants as a function of the temperature. The results depend on the carbon site in the macrocycle thus showing preferences for binding of Na ~. The dipolar relaxation times of the complex were explained on the basis ofpseudorotational motion of the macrocycle which was proved with the MM+ geometry optimisation.