NMR spectroscopic and molecular modelling studies of the solution structure and complexational behaviour of some bis(benzo crown ether)s

Structural information about the bis(benzo crown ether)s I-VI and their com plexes with alkali metal cations was deduced from the C-13 NMR chemical shi fts, the salt-induced H-1 and C-13 chemical shifts and the vicinal H-1,H-1 coupling constants. Especially the isomerism with respect to the amide O=C- NH bonds and imine fragments were assigned by various useful NMR parameters (delta (C=O), (1)J(N,H), (1)J(C,H)) and proved to be E,E-anti,anti. Furthe rmore, stereochemical information about preferred conformations about flexi ble bonds was obtained from 2D ROESY NMR experiments. The complex formation (2:1 complexes and 'sandwich-like' 1:1 complexes, respectively) were deter mined also by Na-23 NMR spectroscopy. The conformational study of the crown ethers was accompanied and corroborated by molecular dynamics and quantum chemical calculations. Copyright (C) 2000 John Wiley & Sons, Ltd.