1H and 13C nuclear magnetic resonance relaxation-time studies of ionophoric calixarene esters

Abstract

H and 13C NMR relaxation times ( T , ) of ethoxycarbonylmethyl derivatives of p-t-butylcalix[n]arenes have been determined at 90 MHz and 36 "C in [2H,]THF. It was found that these calixarenes feature a 'seesaw motion' around the ArCH2Ar linkage as a central support and that this molecular motion is largely suppressed through complexation with Na'.

Multiple field carbon-13 NMR relaxation of calix[4]arene in solution

“…1 H NMR has been widely used since the 1970s to determine the conformations of these compounds. 1 Calix [4]arene can exist in four 'up/down' conformations named cone, partial cone, 1,2 alternate and 1,3 alternate. In solution, calix [4]arene exists predominantly in the cone conformation and 1 H NMR has been a common method used to determine the energy barriers to conformational inversion as a function of solvent and of derivative.…”

“…1 Calix [4]arene can exist in four 'up/down' conformations named cone, partial cone, 1,2 alternate and 1,3 alternate. In solution, calix [4]arene exists predominantly in the cone conformation and 1 H NMR has been a common method used to determine the energy barriers to conformational inversion as a function of solvent and of derivative. 1 Although more recently 13 C NMR has also been applied to the determination of conformation, 3 there have been only three reports in the literature on 13 C NMR relaxation studies of calix [4]arenes.…”

“…In solution, calix [4]arene exists predominantly in the cone conformation and 1 H NMR has been a common method used to determine the energy barriers to conformational inversion as a function of solvent and of derivative. 1 Although more recently 13 C NMR has also been applied to the determination of conformation, 3 there have been only three reports in the literature on 13 C NMR relaxation studies of calix [4]arenes. One study was of a tetraester derivative of calix [4]arene and its Na C complex, 4 another study was of a p-sulfonic acid derivative of calix [4]arene and its pentasodium salt 5 and the third study was of the base calix [4]arene and calix [6]arene in several solvents.…”

“…1,2 The term 'calix' was introduced by Gutsche by analogy to a Greek vase called a 'calix crater. ' The number of phenol units is indicated within brackets in the common name: calix [4]arenes are cyclic tetramers. 1 H NMR has been widely used since the 1970s to determine the conformations of these compounds.…”

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ABSTRACT: Carbon-13 relaxation times and nuclear Overhauser enhancement values were determined for the carbons of calix [4]arene in both CDCl 3 and DMSO-d 6 solvents at magnetic field strengths of 5.9, 9.4, and 14.1 T at 30°C. The relaxation data for the CDCl 3 solution were well described by an isotropic motional model indicating motions in the extreme narrowing limit with a rotational correlation time of 32-38 ps.

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