Abstract-The mass spectra of isomeric 2'-hydroxy-chalcones and flavanones (i.e. 2-phenyl-chroman-4-ones) are essentially identical. Thermal isomerisation prior to ionisation was ruled out. A study of metastable transitions (first and second field free region of a double focusing instrument), as well as low energy spectra of both isomers, pointed towards completely identical fragmentation pathways for the two compounds. Five deuterated compounds were then investigated. The heats of formation of the most important ions were determined. It was concluded that an intramolecular equilibrium exists between a chalcone type and a flavanone type molecular ion.
I N T R O D U C T I O NSEVERAL reports on the mass spectral investigation of chalcones and flavanones have already been pub1ished.l to The mass spectrum of chalcone (I) was first recorded by Beynon :l the major fragmentations of this compound were rationalised and found to be characteristic. Pelter and c o -w o r k e r~~.~ studied the mass spectral behaviour of flavanones. It was not until 1966 that AudieS examined some 2'-hydroxy-~halcones. Some intense peaks in the spectra did not fit into the general breakdown pattern of chalcones. He also noticed that the spectra of chalcones bearing a 2'-hydroxyl function were nearly identical to those of the isomeric flavanones. He proposed an equilibrium between a chalcone type and a flavanone type of molecular ion.The mass spectra of 2'-hydroxy-chalcones and flavanones provide a striking analogy between behaviour under electron-impact and solution chemistry. Indeed, these isomers are known to give the same equilibrium mixture in either basic or acidic solution. ' The mechanism of the isomerisation in aqueous solution involves a proton from the solvent. This of course is impossible in mass spectral rearrangements so that the proton must be one of the molecule itself; the isomerisation has to be intramolecular. In order to check this intramolecular hydrogen shift and to determine the equilibration mechanism, the following compounds were synthesised: 6,977 (1972).
The concentration of polychlorinated biphenyls was shown to progressively increase with maturity in a series of lake trout. The presence of these compounds was determined by column chromatographic isolation, specific detector gas chromatography and mass spectrometry. The relation between fish age and the concentration of polychlorinated biphenyls was highly significant.
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