Sodium ion exchange on the 1,4,7,10,13,16-hexaoxaoctadecanesodium(I) cation ([Na.18C6]+) in several solvents. A sodium-23 nuclear magnetic resonance study

Abstract

²³ Na N.m.r. studies of Na⁺ exchange on the 1,4,7,10,13,16-hexaoxaoctadecanesodium(I) cation ([Na.18C6]⁺) in acetone, methanol and pyridine yield the respective decomplexation rate constants 10^–2k_d(265 K)= 606 ± 88, 42 ± 2 and 7.16 ± 0.30 s^–1; and the corresponding activation parameters ΔH^‡= 36.7 ± 0.7, 53.6 ± 0.8 and 50.5 ± 1.2 kJ mol^–1; and ΔS^‡=–14.0 ± 3.2, 27.8 ± 2.9, and 1.4 ± 4.2 J K^–1 mol^–1. These data are discussed in conjunction with data obtained from other n.m.r. and ultrasonic relaxation studies, and mechanistic aspects of the complexation of Na⁺ by 18C6 are considered.