High energy collision‐induced dissociation of alkali‐metal ion adducts of crown ehters and acyclic analogs

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Abstract
High energy collision-induced dissociation (CID) techniques were applied for structural elucidiation of alkli-metal ion adducts of crown ethers. The CID of alkali-metal adducts of tetraglyme and hexaethylene glycol were also evaluated to contrast the fragmentation pathways of the cyclic ethers with those of acylic analogs. A common fragmentation channel for alkali-metal ion adducts of all the ethers, which results in distonic radical cations, is the homolytic cleavage of carbon—carbon bonds. Additionally, dissociation by carbob—oxygen bond cleavage occurs, and these processes are analogous to the fragmentation pathways observed for simple protonated ethers. The proposed fragmentation pathways for alkali-metal ion adducts of crown ethers result mostly in odd-electron, acyclic product ions. Dissociation of the alkali-metal ion adducts of the acyclic ethers is dominated by losses of various neutral species after an initial hydride or proton transfer. The CID processes for all ethers are independent of alkali-metal ion sizes; however, the extent of dissociation of the complexes to bare alkali-metal ion increases with the size of the metal.