The C-13 NMR spectra of cryptands [2.1.1], [2.2.1], and [2.2.2] in the presence of Li+, Na+, K+, Ca2+, and Ba2+ in D2O/MeOH or CDCl3 have been analyzed. Generally, the carbons shifted to higher field upon complexation. Two exceptions to this were observed: the complexes [2.1.1]·Na+ and [2.2.1]·K+. The C-13 longitudinal relaxation time measurements show a surprising increase in magnitude for most alkali-metal, but not alkaline earth metal, complexes. This increase in relaxation times is interpreted in terms of ligand compression, desolvation, and solvent reorganization.
ASJC Scopus subject areas
- Organic Chemistry