7H-BENZ[KL]ACRIDIN-7-YLIUM CLOSED-SHELL ION PRODUCED FROM 1,8-BIS(PHENYLAMINO)NAPHTHALENES UNDER ELECTRON-IMPACT - TANDEM MASS-SPECTROMETRIC STRUCTURE ELUCIDATION

Not only strongly basic aromatic amines such as 'proton sponges' show characteristic [M - Me2NH - H]+ peaks corresponding to cyclization to stable heterocyclic ions under electron impact. The fragmentation of t he title compounds, which are weak bases, leads to [M - RNH2 - C6H5]heteroaromatic ions. These are the 7-phenyl-7H-benz[kl]acridine radica l cation and the delocalized stable 7H-benz[kl]acridin-7-ylium ion as shown by unimolecular metastable ion spectra, collision-induced decomp osition (CID) tandem mass spectrometry (MS/MS) and accurate mass measu rements. The high-collision-energy CID tandem mass spectra of these io ns are perfectly superimposable on those of the ions produced by the r eference substance, 7-phenyl-7H-benz[kl]acridine obtained as a by-prod uct in the Ullmann phenylation of 1,8-diaminonaphthalene. This combina tion of MS/MS experiments also provides strong support for the gas-pha se reaction mechanism leading to the benz[kl]acridine ions and for the Structures of these ions.