Studies on the N-Oxides of π-Deficient N-Heteroaromatics. XIII. Mass Spectra of Azanaphthalene N-Oxides and Their Photochemical Reaction Products

Abstract

The mass spectra of a series of quinoline 1-oxides have been determined in conjunction with those of the related compounds, such as quinolines and benz [d]-1, 3-oxazepines derived photochemically from these N-oxides. For example, the major decomposition processes of 2-cyanoquinoline 1-oxide (1) are loss of O and loss of CO. Existence of the latter process requires prior formation of a C-O bond and virtually demands isomerization to the corresponding oxaziridine ion (c). This species would then undergo rearrangement to the corresponding benzoxazepine ion (d) before the fragmentation takes place. This supposition seems to be testified by comparison of the spectra of 1 and the corresponding oxazepine (3). The results obtained provide a striking example of parallel behavior of 1 and its related N-oxides in photolysis and electron impact. It is also shown that on electron impact the molecular ions of benz [d]-1, 3-oxazepine derivatives eliminate carbon monoxide as a neutral molecule and the resultant ions behave as indole derivatives. The mass spectrum of 1-cyanoisoquinoline 2-oxide (18), on the contrary, contains M-O and M-(CN)₂ ions, and the occurence of M-CO ion is very weak. The presence of M-(CN)₂ ion can be regarded as a criterion for the intermediary of the corresponding oxazepine ion, since this ion is a base peak in the spectrum of the corresponding photoproduct, benz [f]-1, 3-oxazepine-2-carbonitrile (20). Exceptions from these rules can be explained in terms of the presence of specific structural features, and general decomposition sequences of benz [d]-and benz [f]-1, 3-oxazepines have also been clarified.