Self-Complexation of Macrocyclic Polyethers Studied by Carbon-13 NMR Longitudinal Relaxation Time Measurements and Molecular Mechanics

Article abstract of DOI:10.1021/ja00250a006

Carbon-13 spin-lattice relaxation time measurements on three series of macrocyclic polyethers with ring sizes varying from 15 to 33 ring atoms reveal that 2,6-pyrido (1) and benzo (3) crown ethers with at least 24 ring atoms can adopt conformations in which the aromatic moiety is encapsulated by the polyether ring of the ligand.This type of intramolecular self-complexation is not observed in the case of 1,3-xylyleno crown ethers (2).A number of possible structures of self-complexed crown ethers could be generated and studied by molecular mechanics.The calculations indicate that the nature of the driving force for self-complexation of 2,6-pyrydo crown ethers is mainly electrostatic whereas van der Waals forces favor self-complexation of benzo crown ethers.