CS-133, H-1 2-DIMENSIONAL HETERONUCLEAR OVERHAUSER EFFECT SPECTROSCOPY (HOESY) - STRUCTURAL-ANALYSIS OF ORGANIC CESIUM COMPOUNDS BY DETECTION OF SHORT CS,H CONTACTS

Transient heteronuclear Overhauser effects were observed between Cs-133 and H-1 by two-dimensional heteronuclear Overhauser effect spectroscopy (HOESY). In caesium tetraphenylborate (CsBPh4) dissolved in pyridine-d5, Cs+ is tightly attached to the BPh4- anion, thus forming a contact ion pair (CIP). By contrast, after addition of one equivalent of the crown ether 18-crown-6, caesium is located intimately at the site of the crown ether whereas the tetraphenylborate anion is remote (solvent-separated ion pair, SSIP). The results are in agreement with experiments described earlier by Mei et al. Similar observation were made for caesium 3-methylpentyl 3-oxide in tetrahydrofuran-d8 solution. Cs-133, H-1 HOESY indicates the presence of a contact ion pair. Steady-state Cs-133 {H-1} experiments on the latter compound reveal weak fractional enhancements of 0.2%.