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Papers by Patricia Allegretti
Journal of Applied Solution Chemistry and Modeling, Dec 31, 2012
Abstrac t : 2-cyanobenzoic acids are very important compounds in several sciences, and it is beca... more Abstrac t : 2-cyanobenzoic acids are very important compounds in several sciences, and it is because of this that studying their tautomeric equilibria is of great interest. Ring-chain tautomeric equilibria of 2-, 3-and 4-cyanobenzoic, 3benzyl-2-cyanobenzoic and 1-cyano-2-naphthoic acids were studied in gas phase by means of mass spectrometry (MS). Furthermore, evidences of ring-chain tautomerism of 2-cyanobenzoic acid were found in solution using 1 H and 13 C nuclear magnetic resonance and in solid phase by infrared spectroscopy.
Spectrochimica Acta Part a Molecular and Biomolecular Spectroscopy, Feb 1, 2011
The study of tautomerics equilibria is really important because the reactivity of each compound w... more The study of tautomerics equilibria is really important because the reactivity of each compound with tautomeric capacity can be determined from the proportion of each tautomer. In the present work the tautomeric equilibria in some γ,δ-unsaturated β-hydroxynitriles and γ,δ-unsaturated β-ketonitriles were studied. The first family of compounds presents two possible theoretical tautomers, nitrile and ketenimine, while the second one presents four possible theoretical tautomers, keto-nitrile, enol (E and Z)-nitrile and keto-ketenimine. The equilibrium in gas phase was studied by gas chromatography-mass spectrometry (GC-MS). Tautomerization enthalpies were calculated by this methodology, and results were compared with those obtained by density functional theory (DFT) calculations, observing a good agreement between them. Nitrile tautomers were favored within the first family of compounds, while keto-nitrile tautomers were favored in the second family.
Intramed Journal, Nov 21, 2012
Spectrochimica Acta Part a Molecular and Biomolecular Spectroscopy, Feb 1, 2009
Butoxylated silica nanoparticles (BSN) were prepared by esterification of the silanol groups of f... more Butoxylated silica nanoparticles (BSN) were prepared by esterification of the silanol groups of fumed silica nanoparticles with butanol and characterized by 13C and 29Si NMR and thermogravimetry. The molecular probes benzophenone (BP) and safranine-T were used to investigate the BSN suspensions in water:acetonitrile. Laser flash-photolysis experiments at λexc = 266 nm performed with BSN suspended in acetonitrile:aqueous phosphate buffer supported previous results of our group obtained by time-resolved phosphorescence experiments and showed that only free and adsorbed excited triplet states of BP and diphenylketyl radicals contribute to the signals. The UV-vis spectroscopic and photophysical properties of safranine-T are strongly solvent-dependent. Thus, the analysis of the emission spectra and fluorescence lifetimes yielded information on the localization of this probe molecule in suspensions of BSN and of the bare silica nanoparticles. The values of the equilibrium constant for the adsorption of the ground-state safranine-T on the particles were found to be (9.2 ± 0.8) × 10 4, (7.2 ± 0.8) × 10 5, and (3.0 ± 0.1) × 10 4 for the BSN in 1:1 acetonitrile:water, SiO 2 in 1:1 acetonitrile:water, and SiO 2 in acetonitrile, respectively.
Journal of Applied Solution Chemistry and Modeling, Oct 15, 2012
ketoamides are versatile intermediates for the synthesis of several heterocycles and they are als... more ketoamides are versatile intermediates for the synthesis of several heterocycles and they are also relevant compounds in biological systems, with their tautomeric equilibria being a crucial aspect to be studied in order to understand their chemical and biological behaviour. Tautomeric equilibria of a series of -ketobutanamides were analyzed by means of 1 HNMR, determining that ketoamide and Z-enolamide are the main tautomeric species in solution, both presenting internal hydrogen bonds. Keto-enol equilibrium predominates over other possible tautomerisms (e.g. amide-imidol). The enol tautomer appears to be favoured by electron withdrawing substituents and non-protic solvents. Thermodynamic parameters H and S were determined in CDCl3 and DMSO-d6, showing that the keto-enol equilibria are exothermic and require a molecule order increase.
Chem Biol Inter, 2002
Mass spectra of some amides and thioamides under different sample introduction temperatures and i... more Mass spectra of some amides and thioamides under different sample introduction temperatures and ionization electron energies are reported and analysed along with the corresponding theoretical calculations.
Kinetics and Catalysis, 2002
ABSTRACT Aromatic hydrocarbons are susceptible to direct acylation by benzoic acids with high yie... more ABSTRACT Aromatic hydrocarbons are susceptible to direct acylation by benzoic acids with high yields bearing ortho or para alkyl groups as substituents under Friedel–Crafts reaction conditions. The a-H of the alkyl moiety seems to be responsible for the observed relatively high reaction rates of conversion. Carbanion-like species are proposed as reaction intermediates, which also operate as strong bases in the reaction rate-determining steps. Trapping experiments, deuterium isotopic effects, and kinetics data favor a concerted reaction pathway where proton transfer from the hydrocarbon molecule to a carbanionic intermediate takes place with a simultaneous electrophilic attack of the carbonylic carbon atom.
J Mol Struct, 2001
The gas chromatographic behaviour for some β-ketoesters was studied. Additionally, the feasibilit... more The gas chromatographic behaviour for some β-ketoesters was studied. Additionally, the feasibility of the gas chromatographic separation of the corresponding tautomer forms was examined. In this work mass spectrometric detection allowed identification of both keto and enol forms and an estimation of their relative amounts for methylacetoacetate, α-chloromethylacetoacetate, ethylacetoacetate and α-chloroethylacetoacetate. This finding demonstrates slow tautomerisation kinetics permitting the chemical identity maintenance of the tautomers.
Among carbonyl compounds esters are not usually involved in tautomeric equilibrium with the excep... more Among carbonyl compounds esters are not usually involved in tautomeric equilibrium with the exception of β-ketoesters and thioesters. We show that mass spectrometry data are helpful in demonstrating the occurrence of the enol structure for thioesters, particularly significant for the dithio analogues. AM1 semiempirical MO calculations are also consistent with the experimental results.
Journal of Molecular Structure: THEOCHEM, 2000
The enolisation degree of ketones is generally favoured by the increase of the steric effect exer... more The enolisation degree of ketones is generally favoured by the increase of the steric effect exerted by the substitution a to the carbonyl group. The analysis of the corresponding mass spectra has allowed us to assign unambiguously some fragmentations to speci®c tautomers and to establish an acceptable correlation between the corresponding ion abundance ratios and the AM1 MO theoretical calculation of the approximate enolisation equilibrium constants. q
Tautomerism in organic chemistry has been extensively studied in condensed phase by spectrometric... more Tautomerism in organic chemistry has been extensively studied in condensed phase by spectrometric methods, mainly by IR and NMR techniques. Mass spectrometry studies start 40 years ago but just recently it has been recognized the importance of the mass spectral data for the study of tautomerism in the gas phase. Mass spectrometry can provide valuable information in regard to tautomeric
Journal of Molecular Structure, 2015
ABSTRACT The beta-ketonitrile 2-methyl-5-phenyl-3-oxo-4-pentenenitrile, a polymerizable monomer, ... more ABSTRACT The beta-ketonitrile 2-methyl-5-phenyl-3-oxo-4-pentenenitrile, a polymerizable monomer, exists in two important tautomeric forms, keto and enol isomers. This compound has been studied as monomer in polymerization reactions and the resulting polymers have been applied in fields of nanotechnology. Currently, these are being studied in nanomedicine. To understand the tautomeric equilibrium, we have studied this compound in solution by NMR spectrometry. Correlation with DFT calculations has been carried out in order to understand the system behavior. The results found in this work, both by experiments and calculations, show that the enol content increases with solvent polarity.
Journal of Molecular Structure: THEOCHEM, 2002
Mass spectra of some amides and thioamides under different sample introduction temperatures and i... more Mass spectra of some amides and thioamides under different sample introduction temperatures and ionization electron energies are reported and analysed along with the corresponding theoretical calculations.
The Open Physical Chemistry Journal, 2009
Afinidad Revista De Quimica Teorica Y Aplicada, 2000
Journal of Applied Solution Chemistry and Modeling, Dec 31, 2012
Abstrac t : 2-cyanobenzoic acids are very important compounds in several sciences, and it is beca... more Abstrac t : 2-cyanobenzoic acids are very important compounds in several sciences, and it is because of this that studying their tautomeric equilibria is of great interest. Ring-chain tautomeric equilibria of 2-, 3-and 4-cyanobenzoic, 3benzyl-2-cyanobenzoic and 1-cyano-2-naphthoic acids were studied in gas phase by means of mass spectrometry (MS). Furthermore, evidences of ring-chain tautomerism of 2-cyanobenzoic acid were found in solution using 1 H and 13 C nuclear magnetic resonance and in solid phase by infrared spectroscopy.
Spectrochimica Acta Part a Molecular and Biomolecular Spectroscopy, Feb 1, 2011
The study of tautomerics equilibria is really important because the reactivity of each compound w... more The study of tautomerics equilibria is really important because the reactivity of each compound with tautomeric capacity can be determined from the proportion of each tautomer. In the present work the tautomeric equilibria in some γ,δ-unsaturated β-hydroxynitriles and γ,δ-unsaturated β-ketonitriles were studied. The first family of compounds presents two possible theoretical tautomers, nitrile and ketenimine, while the second one presents four possible theoretical tautomers, keto-nitrile, enol (E and Z)-nitrile and keto-ketenimine. The equilibrium in gas phase was studied by gas chromatography-mass spectrometry (GC-MS). Tautomerization enthalpies were calculated by this methodology, and results were compared with those obtained by density functional theory (DFT) calculations, observing a good agreement between them. Nitrile tautomers were favored within the first family of compounds, while keto-nitrile tautomers were favored in the second family.
Intramed Journal, Nov 21, 2012
Spectrochimica Acta Part a Molecular and Biomolecular Spectroscopy, Feb 1, 2009
Butoxylated silica nanoparticles (BSN) were prepared by esterification of the silanol groups of f... more Butoxylated silica nanoparticles (BSN) were prepared by esterification of the silanol groups of fumed silica nanoparticles with butanol and characterized by 13C and 29Si NMR and thermogravimetry. The molecular probes benzophenone (BP) and safranine-T were used to investigate the BSN suspensions in water:acetonitrile. Laser flash-photolysis experiments at λexc = 266 nm performed with BSN suspended in acetonitrile:aqueous phosphate buffer supported previous results of our group obtained by time-resolved phosphorescence experiments and showed that only free and adsorbed excited triplet states of BP and diphenylketyl radicals contribute to the signals. The UV-vis spectroscopic and photophysical properties of safranine-T are strongly solvent-dependent. Thus, the analysis of the emission spectra and fluorescence lifetimes yielded information on the localization of this probe molecule in suspensions of BSN and of the bare silica nanoparticles. The values of the equilibrium constant for the adsorption of the ground-state safranine-T on the particles were found to be (9.2 ± 0.8) × 10 4, (7.2 ± 0.8) × 10 5, and (3.0 ± 0.1) × 10 4 for the BSN in 1:1 acetonitrile:water, SiO 2 in 1:1 acetonitrile:water, and SiO 2 in acetonitrile, respectively.
Journal of Applied Solution Chemistry and Modeling, Oct 15, 2012
ketoamides are versatile intermediates for the synthesis of several heterocycles and they are als... more ketoamides are versatile intermediates for the synthesis of several heterocycles and they are also relevant compounds in biological systems, with their tautomeric equilibria being a crucial aspect to be studied in order to understand their chemical and biological behaviour. Tautomeric equilibria of a series of -ketobutanamides were analyzed by means of 1 HNMR, determining that ketoamide and Z-enolamide are the main tautomeric species in solution, both presenting internal hydrogen bonds. Keto-enol equilibrium predominates over other possible tautomerisms (e.g. amide-imidol). The enol tautomer appears to be favoured by electron withdrawing substituents and non-protic solvents. Thermodynamic parameters H and S were determined in CDCl3 and DMSO-d6, showing that the keto-enol equilibria are exothermic and require a molecule order increase.
Chem Biol Inter, 2002
Mass spectra of some amides and thioamides under different sample introduction temperatures and i... more Mass spectra of some amides and thioamides under different sample introduction temperatures and ionization electron energies are reported and analysed along with the corresponding theoretical calculations.
Kinetics and Catalysis, 2002
ABSTRACT Aromatic hydrocarbons are susceptible to direct acylation by benzoic acids with high yie... more ABSTRACT Aromatic hydrocarbons are susceptible to direct acylation by benzoic acids with high yields bearing ortho or para alkyl groups as substituents under Friedel–Crafts reaction conditions. The a-H of the alkyl moiety seems to be responsible for the observed relatively high reaction rates of conversion. Carbanion-like species are proposed as reaction intermediates, which also operate as strong bases in the reaction rate-determining steps. Trapping experiments, deuterium isotopic effects, and kinetics data favor a concerted reaction pathway where proton transfer from the hydrocarbon molecule to a carbanionic intermediate takes place with a simultaneous electrophilic attack of the carbonylic carbon atom.
J Mol Struct, 2001
The gas chromatographic behaviour for some β-ketoesters was studied. Additionally, the feasibilit... more The gas chromatographic behaviour for some β-ketoesters was studied. Additionally, the feasibility of the gas chromatographic separation of the corresponding tautomer forms was examined. In this work mass spectrometric detection allowed identification of both keto and enol forms and an estimation of their relative amounts for methylacetoacetate, α-chloromethylacetoacetate, ethylacetoacetate and α-chloroethylacetoacetate. This finding demonstrates slow tautomerisation kinetics permitting the chemical identity maintenance of the tautomers.
Among carbonyl compounds esters are not usually involved in tautomeric equilibrium with the excep... more Among carbonyl compounds esters are not usually involved in tautomeric equilibrium with the exception of β-ketoesters and thioesters. We show that mass spectrometry data are helpful in demonstrating the occurrence of the enol structure for thioesters, particularly significant for the dithio analogues. AM1 semiempirical MO calculations are also consistent with the experimental results.
Journal of Molecular Structure: THEOCHEM, 2000
The enolisation degree of ketones is generally favoured by the increase of the steric effect exer... more The enolisation degree of ketones is generally favoured by the increase of the steric effect exerted by the substitution a to the carbonyl group. The analysis of the corresponding mass spectra has allowed us to assign unambiguously some fragmentations to speci®c tautomers and to establish an acceptable correlation between the corresponding ion abundance ratios and the AM1 MO theoretical calculation of the approximate enolisation equilibrium constants. q
Tautomerism in organic chemistry has been extensively studied in condensed phase by spectrometric... more Tautomerism in organic chemistry has been extensively studied in condensed phase by spectrometric methods, mainly by IR and NMR techniques. Mass spectrometry studies start 40 years ago but just recently it has been recognized the importance of the mass spectral data for the study of tautomerism in the gas phase. Mass spectrometry can provide valuable information in regard to tautomeric
Journal of Molecular Structure, 2015
ABSTRACT The beta-ketonitrile 2-methyl-5-phenyl-3-oxo-4-pentenenitrile, a polymerizable monomer, ... more ABSTRACT The beta-ketonitrile 2-methyl-5-phenyl-3-oxo-4-pentenenitrile, a polymerizable monomer, exists in two important tautomeric forms, keto and enol isomers. This compound has been studied as monomer in polymerization reactions and the resulting polymers have been applied in fields of nanotechnology. Currently, these are being studied in nanomedicine. To understand the tautomeric equilibrium, we have studied this compound in solution by NMR spectrometry. Correlation with DFT calculations has been carried out in order to understand the system behavior. The results found in this work, both by experiments and calculations, show that the enol content increases with solvent polarity.
Journal of Molecular Structure: THEOCHEM, 2002
Mass spectra of some amides and thioamides under different sample introduction temperatures and i... more Mass spectra of some amides and thioamides under different sample introduction temperatures and ionization electron energies are reported and analysed along with the corresponding theoretical calculations.
The Open Physical Chemistry Journal, 2009
Afinidad Revista De Quimica Teorica Y Aplicada, 2000