Decay sequences - ion series of mass spectra of benzene, 1,3,5,7-cyclooctatetraene, [18]-annulene, hexafluorobenzene and its isomers

Abstract

: This research is devoted to the results of the analysis of decay sequences - ion mass spectra of benzene, 1,3,5,7-cyclooctatetraene, [18]-annulene, as well as hexafluorobenzene and its homologues. The difference between the primary abstraction groups in the spectra of benzene: . H, CH, . C 2 H,C 3 H 3 , C 4 H 2 , . C 5 H 3 and hexafluorobenzene: . F and CF contradicts the analogy of their fragmentation pathways. Upon ionization and removal of one of the six π -electrons of benzene, its + . M cation-radical arises with the corresponding excitation energy and one of five variants of rearrangement of conjugations of π -electrons of its carbon core. The mass spectrum of benzene consists of six series of fragment ions. The first series of ions, including the successive detachment of six hydrogen atoms with the formation of the + C 6 ion, is the result of the fragmentation of the excited + . M 1 , in which the existing π -conjugations of the carbon cycle are preserved and their rearrangement does not occur. The primary detachments of the CH, . C 2 H, C 3 H 2 , C 4 H 2 , and . C 5 H 3 groups of five other ionic series confirm that in excited + . M benzene, five variants of rearrangement of π consist of 6, 18, and 8 series of ions, respectively, the number of which corresponds to the number of carbon atoms of these cycles. This coincidence is the result of the fact that, during the fragmentation of excited molecular radical cations, all possible variants of the rearrangement of their π -conjugations are realized, as well as the fragmentation variant-with the preservation of existing conjugations, when only the abstraction of hydrogen atoms occurs. The ionic series of benzene, 1,3,5,7-cyclooctatetraene C 8 H 8 , and [18]-annulene C 18 H 18 fragment without branching or intersecting. In contrast to the six ionic series of benzene, hexafluorobenzene fragments with the formation of two series, that differ in the sequence of detachments. One of the series of ions includes successive abstractions of four fluorine atoms, CF and . F to form the + C 5 ion. The other, after the primary detachment of the CF, branches, fragmenting both with the detachment of the CF and with the detachment of the . F. In contrast to the ionic series of the mass spectrum of benzene, in the spectra of hexafluorobenzene and its isomers, the rearrangement of π -conjugations of the ring does not occur, since none of the two ionic series formed is the result of the appearance of any new π -conjugation.