The electron impact induced fragmentations of the five possible naphthoflavones have been studied with the aid of low-and high-resolution measurements, metastable decompositions and isotope labelling using either deuterium or carbon-13 atoms. All compounds show both the direct expulsion of a CO residue from the carbonyl group and the retro Diels-Alder cleavage. The abundant [M -HI+ ion has been formulated as the substituted P-tropolone species, which, in the case of P-naphthoflavone, is in competition with a pentacyclic species arising from the elimination of H-5 as evidenced in the spectrum of 5-d-P-naphthoflavone. Other previously unsuspected ions are also in evidence.
Received
Studies of the genesis of the [ M -H] + ion in flavanone and 2'-hydroxychalcone, performed with the aid of metastable decompositions and deuterium labelling, allow new structural notations to be postulated for the I M -HI + ions, which in turn provide evidence for the pathways in the [ M -H -ketenel+ fragmentation routes for these compounds.
Further evidence supporting the structure of the [M -1]+ ion found in the mass spectrum of flavone as being the [dibenzo-0-tropolone -HI+ species was obtained by comparison of linked scan measurements performed in flavone, 3-deuteroflavone, 5,6,7,8-tetradeuteroflavone, 2',3',4',5',6'-pentadeuteroflavone and dibenzo-6tropolone. This fragmentation process has also been demonstrated in the case of 3-methoxyflavone by high-resolution measurements, deuterium labelling, metastable decompositions and evaluation of the subspectra of 9-methoxyfluorenol, fluorenone and biphenylene. The structure of the ion at m / z 181 in the spectrum of flavone was found to be the 12-phenylbenzoxetane -1]+ species.
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