Chemistry of crown ethers: the mass spectra of macrocyclic polyethers

Abstract

A detailed evaluation of the mass spectral fragmentation patterns of several series of crown ethers has been made. Included are compounds containing one or two aromatic or heteroaromatic rings linked through carbon atoms to polyether chains of various lengths. Although such molecules are highly functionalized and have high molecular weights, molecular ion peaks were always observed, and a large percentage of the total ion current was carried by a small number of fragment ions. Only small differences were observed in the mass spectra of compounds having different aromatic ring substitution patterns. The fragmentation patterns for each set of compounds pointed to the formation of fragment ions in which the positive charge was localized on: (i) ions containing only polyether ring carbon and oxygen atoms; in the majority of cases such an ion (protonated ethylene oxide at m/e 45) provided the base peak: (ii) ions containing the aromatic (heteroaromatic) nucleus and no polyether ring carbon atoms; (iii) ions containing the aromatic (heteroaromatic) nucleus together with part of the polyether chain. High resolution measurements and metastable analysis provided confirmation for the postulated fragmentation mechanisms and product ion structures. Hydrogen and carbon rearrangements are involved in some cases. Components of higher molecular weight crown ether mixtures have been identified by mass spectrometry on the basis of their molecular ion peaks.