The mass spectra of 1,2-€diphenyl‐pyrazolidine-€3,5-dione and twenty‐one 4‐substituted derivatives are reported. Their fragmentation patterns have been studied by deuterium labelling, exact mass measurements, metastable studies by the defocusing technique and low energy spectra. Hydrogen rearrangements from the 4‐position of the heterocycle and/or from the ß‐position of the 4‐substituent groups, lead to the main primary fragment ions [C12H11N2]+ (m/e 183) as shown by the metastables. The 4,4‐d2 derivative shows an appreciable isotope effect even for molecular ions decomposing in the ion source. By comparison with the metastable abundances of competitive reactions, the molecular ions (m/e 252) of the 4‐unsubstituted compound appear to be structurally different from the corresponding m/e 252 fragment ions formed from 4‐derivatives by the loss of 4‐substituent with H rearrangement. If only vinylic or aromatic hydrogen atoms are present, primary cleavage of the heterocyclic ring occurs with loss of OH·, C3O2 and C3HO2. Important rearrangements leading to elimination of C6H6N and C6H7N are typical for unsaturated substituents on position four having allylic hydrogen atoms. Fragment ions, identical to molecular ions of some compounds discussed here, are obtained by electron‐impact and/or thermal decompostion of some complex compounds containing more than one 1,2‐diphenyl‐pyrazolidine‐3,5‐dione system. The [C6H5N2]+ (m/e 105) and [C6H5]+ (m/e 77) ions are common fragments of all the title compounds. Any hydrogen scrambling reactions between phenyl and heterocycle or 4‐substituent groups can be excluded. Copyright © 1975 Heyden & Son Ltd.

Mass spectrometry of heterocyclic compounds VIII–electron‐impact‐induced fragmentation of 1,2‐diphenyl‐pyrazolidine‐3,5‐dione and some 4‐substituted derivatives

Citterio, Attilio;
1975-01-01

Abstract

The mass spectra of 1,2-€diphenyl‐pyrazolidine-€3,5-dione and twenty‐one 4‐substituted derivatives are reported. Their fragmentation patterns have been studied by deuterium labelling, exact mass measurements, metastable studies by the defocusing technique and low energy spectra. Hydrogen rearrangements from the 4‐position of the heterocycle and/or from the ß‐position of the 4‐substituent groups, lead to the main primary fragment ions [C12H11N2]+ (m/e 183) as shown by the metastables. The 4,4‐d2 derivative shows an appreciable isotope effect even for molecular ions decomposing in the ion source. By comparison with the metastable abundances of competitive reactions, the molecular ions (m/e 252) of the 4‐unsubstituted compound appear to be structurally different from the corresponding m/e 252 fragment ions formed from 4‐derivatives by the loss of 4‐substituent with H rearrangement. If only vinylic or aromatic hydrogen atoms are present, primary cleavage of the heterocyclic ring occurs with loss of OH·, C3O2 and C3HO2. Important rearrangements leading to elimination of C6H6N and C6H7N are typical for unsaturated substituents on position four having allylic hydrogen atoms. Fragment ions, identical to molecular ions of some compounds discussed here, are obtained by electron‐impact and/or thermal decompostion of some complex compounds containing more than one 1,2‐diphenyl‐pyrazolidine‐3,5‐dione system. The [C6H5N2]+ (m/e 105) and [C6H5]+ (m/e 77) ions are common fragments of all the title compounds. Any hydrogen scrambling reactions between phenyl and heterocycle or 4‐substituent groups can be excluded. Copyright © 1975 Heyden & Son Ltd.
1975
€pyrazolidine-€3,5-dione , mass spectrometry, mechanism
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11311/1047375
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