Carbon-13 NMR Longitudinal Relaxation Time Study of an Ionophoric 1,3-Alternate-Shaped Calix[4]arene Ester

Abstract

Abstract:The carbon-13 NMR longitudinal relaxation times (T 1 ) studies on the 1,3-alternate-shaped calix[4]arene possessing two ester groups 1 in the absence and the presence of Na were carried out for the first time. The T 1 values were measured under proton-noisedecoupling conditions by the inversion-recovery technique. The T 1 -value of 1 is primarily governed by dipole-dipole relaxation. When calixarene 1 forms an ensemble with Na , the T 1 -values for all carbons are decreased. This suggests that the molecular motion of species 1 is efficiently frozen through complexation with Na . Eventually, Na ion plays an important role as a template ion specifically to freeze the fluctuational motion of two ethoxycarbonylmethoxybenzene units of 1.

Synthesis, Structure and Magnetic Properties of Some Copper(II) Complexes Supported by Pendant Calix[4]arene Ligands

“…For the cone conformation chemical shifts at 30–32 ppm are diagnostic. For the 1,3‐ alternate conformation the chemical shifts are more downfield in the 37–39 ppm range [40] . The separation of the pair of doublets for the two diastereotopic methylene protons Δδ is also diagnostic (Δδ>0.2 ppm: cone conformation; Δδ≤0.2 ppm: 1,3‐ alternate conformation) [41] .…”

“…For the 1,3-alternate conformation the chemical shifts are more downfield in the 37-39 ppm range. [40] The separation of the pair of doublets for the two diastereotopic methylene protons Δδ is also diagnostic (Δδ > 0.2 ppm: cone conformation; Δδ � 0.2 ppm: 1,3-alternate conformation). [41] For L1 and L2 the corresponding separations amount to Δδ = 0.67 and 1.26 ppm, respectively, in agreement with the cone conformation.…”