, Volume 21, Issue 12, pp 1368-1374

Negative ion mass spectra and structure of 4-substituted 1-phenyl-3-methyl-5-pyrazolones

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This is the first study of the electron capture dissociative resonance (ECDR) mass spectra of 4-substituted 1-phenyl-3-methyl-5=pyrazolones. The major features of the fragmentation of these compounds under ECDR. conditions were found relative to their substituent properties. After loss of the methyl group from the nitrogen atom, the pyrazolone ring isomerizes to a pyrazole ring with localization of the negative charge on the oxygen atom of the carbonyl group. The intensity of the [M - Ch3] fragment depends on the substituent properties.