Mass spectral and theoretical studies on the tautomerism of selected thioesters

Allegretti, Patricia Ercilia; Asens, Daniel; Schiavoni, María de las Mercedes; Bravo, Rodolfo D.; Castro, Eduardo A.; Furlong, Jorge

doi:10.3998/ark.5550190.0004.f15

Cited by 6 publications

(8 citation statements)

References 15 publications

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“…In order to confirm the previous assumption about tautomer V , mass spectrum of 2-thiouracil ( 5 ) was measured and it is shown in Figure 5. If tautomer V was present in this compound (which would be more plausible than for uracil according to previous studies 16,25 ), then a fragmentation pathway analogous to Scheme 4 should take place and give a peak at m/z 101. Such peak is not detectable in the spectrum of 5 and then it supports the assumption that tautomer V is not present.…”

Section: Resultsmentioning

confidence: 68%

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Tautomerism of uracil and related compounds: A mass spectrometry study

Colasurdo

Pila

Iglesias

et al. 2017

Eur J Mass Spectrom (Chichester)

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It has been demonstrated that uracil has a preponderant tautomeric form, but it is also known that different tautomers co-exist in this equilibrium. In this work, mass spectrometry is used as a helpful tool to analyse the equilibria, using derivative compounds to forbid the presence of some tautomers and ion trap mass spectrometry to follow relevant fragmentation pathways. Theoretical calculations were performed to confirm tautomers abundance by energy minimization in gas phase. Analysis of mass spectra of uracil, three methyl-substituted uracils, 2-thiouracil and three benzouracils suggest that uracil exists mainly as three tautomers in gas phase: one major structure that corresponds to the classical structure of uracil (pyrimidine-2,4(1H,3H)-dione) bearing two carbonyls and two NH moieties, and two minor enolic forms (4-hydroxypyrimidin-2(1H)-one and 2-hydroxypyrimidin-4(1H)-one). Such tautomeric distribution is supported by theoretical calculations, which show that they are the three most stable tautomers.

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Section: Resultsmentioning

confidence: 68%

“…Several studies on the tautomeric equilibrium of diverse families of compounds have been carried out in our laboratory and, so far, mass spectrometry and semi-empirical calculations have proved to constitute powerful tools for prediction of fast equilibrium occurrence. 16 This methodology approach has been used in this work.…”

Section: Introductionmentioning

confidence: 99%

Tautomerism of uracil and related compounds: A mass spectrometry study

Colasurdo

Pila

Iglesias

et al. 2017

Eur J Mass Spectrom (Chichester)

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“…As was demonstrated for keto-enol tautomerism of a series of 1-and 3-substituted acetylacetones [73] and a variety of carbonyl and thiocarbonyl compounds [74][75][76][77][78][79][80][81][82][83], there is no significant interconversion of tautomeric forms in the gas phase following electron impact ionization in the mass spectrometer, i.e., molecular ions M + • do not undergo unimolecular tautomerization. It is even more surprising that, once the solvent is separated after injection in GC-MS experiments, neither intermolecular nor unimolecular mechanism of tautomeric transformation is operative even with no GC separation.…”

Section: Gas Chromatography-mass Spectrometry Determinationsmentioning

confidence: 99%

“…Correlation of the results obtained by GC-MS with those of semiempirical molecular orbitals calculations for amides, ureas, hydantoins, isoquinolinones, ketones, diketones, and lactones demonstrated that mass spectrometry provides an adequate tool for predicting tautomeric equilibrium shifts within a series of organic compounds [74][75][76][77][78][79][80][81][82][83].…”

Section: Gas Chromatography-mass Spectrometry Determinationsmentioning

confidence: 99%

Mass spectrometry as a tool for studying tautomerism

et al. 2008

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“…The combination of MS and theoretical calculations, which has been widely used in our laboratory, is a powerful tool to study rapid equilibrium processes. 17,18 Theoretical optimization of the tautomeric forms of Pendimethalin was performed using Gaussian software 19 with the B3LYP level of theory and 6-31G(d,p) plus 6-311++G(d,p) as basis sets to support experimental data. was obtained by selective reduction.…”

Section: Introductionmentioning

confidence: 99%

Evidence of the presence of minor tautomeric forms in selected nitroanilines

Colasurdo

Pila

Laurella

et al. 2020

Rapid Comm Mass Spectrometry

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RationaleNitroanilines can exist in several tautomeric forms: nitro‐amino, nitro‐imino, and aci‐imino. The importance of evaluating minor tautomeric species comes from the fact that even less abundant tautomers have been proved to play important roles in reaction mechanisms.MethodsElectron ionization mass spectra of the pesticide Pendimethalin and four related nitroanilines were recorded at 70 eV to find information about the presence of minor tautomeric forms in the gas phase. The existence of the possible tautomers was evaluated by studying specific fragmentation pathways, which were confirmed by tandem mass spectrometry (MS/MS) experiments. Further supporting information was obtained by studying the structures of some intermediate compounds by theoretical calculations at the B3LYP 6‐311++G(d,p) level.ResultsThe mass spectrum of Pendimethalin suggests the coexistence of the nitro‐amine tautomer (the most stable form) with four possible less stable tautomers in equilibrium. The fragmentation routes were used to explain analogous peaks in two related compounds. However, the spectra of two other related compounds that cannot follow the proposed route of fragmentation for nitro‐imine tautomers do not show the analogous peak. Theoretical calculations were used to correlate the precursor cation with the proposed fragmentation pathway.ConclusionsBy the study of mass spectra and proposed fragmentation pathways it can be concluded that, although the nitro‐amine is the most abundant species within the system, minor tautomers (nitro‐imine and aci‐imine) coexist in the gas phase.

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Mass spectral and theoretical studies on the tautomerism of selected thioesters

Cited by 6 publications

References 15 publications

Tautomerism of uracil and related compounds: A mass spectrometry study

Tautomerism of uracil and related compounds: A mass spectrometry study

Mass spectrometry as a tool for studying tautomerism

Evidence of the presence of minor tautomeric forms in selected nitroanilines

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