ATAQUE NUCLEOFILICO PDF

Daniela Ivón Fernández Ayala. Sexto Semestre. QFB. Ataque Nucleofílico. likes · 28 talking about this. Personal Blog. A partir de nuestros resultados, se encontró que un ataque electrofílico permite un ataque nucleofílico, entonces es necesario un segundo ataque mediante.

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In order to observe systematically how the pyridine nitrogen atom acquires electrophilic character and analyze the proposals made by Gibson et al.

The electronic density of the phosphorus and carbon atoms of the phosphite ligand is also expected to decrease in the nitrosyl complex. Even while 7 is stable for extended periods at room temperature, the ligand was easily deprotonated at the imine methyl group with loss of methane [7, 25].

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The trend of the experimental values for the halogen hardness, places the C 6 H 5 NH 2 and Me nucleophiles as soft and softer groups respectively: Peica et al studied tartrazine from both experimental and theoretical point of views [26].

Chattaraj, Taylor and Francis, Boca Raton, The spectra were recorded from to nm. In the gas phase, the more reactive sites for an electrophilic, nucleophilic and free radical attacks were 18C, 2Na and 17N respectively. The total energy for tartrazine calculated under this condition was Methodology A starting geometry was generated using the PM6 method [61] implemented nucleofilcio Mopac [62].

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Supplementary Information Supplementary data are available free of charge at http: Nkcleofilico, from HSAB principle and the Density Functional Theory, it has been possible to identify many useful and important reactivity concepts as the Fukui Function [ 42, 43]. The N-methylation was unequivocally confirmed by a single-crystal X-ray diffraction experiment [6].

However, to our knowledge, a determination of the global and local reactivity descriptors of tartrazine is still missing.

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Moreover, tartrazine has been associated with allergic reactions [3, 4], hyperactivity [10], behavioral problems [11, asthma [12, 13], migraines, thyroid cancer, among other ills [14].

Finally, if tartrazine is initially attacked by a free radical then, a subsequent attack by a nucleophile will be necessary to cleave the azo bond. Karplus University of Washington. They reported a vibrational Raman characterization of this dye at different pH values [26]. Therefore, the nucleophilic attack at the pyridine nitrogen depends fundamentally on stereoelectronic rather than on steric factors cf.

Last results suggest that some methods focused to degrade tartrazine must be improved in order to be applied at industrial level.

However, a first attack on tartrazine by a nucleophile only would cause a nucleophilic substitution of Na atoms. A subsequent electrophilic or free radical attack will be necessary to cause the cleavage of the azo bond, see Figure 4b. Since 5ac has no ortho substitution in the N -phenyl ring, the nucleophilic attack at the pyridine nitrogen atom does not depend on steric factors.

A frequency analysis was applied to the optimized geometries to verify the stability criterion, in all cases the frequency values were positive and its values were coincident with those reported in the literature [26]. Received April 8 thAccepted June 17 th This result suggests that tartrazine stability diminishes in the aqueous phase. This fact and its water soluble nature have caused that tartrazine is considered as a persistent contaminant in industrial effluents [6].

In this perspective, it is likely that the reactions take place in the solid state and in solution following two different pathways Scheme 1. The reported Mulliken charge on the ligand by the absence and presence of the ether molecule was A38, Glutationa e enzimas relacionadas: However, the value of this function is completely dependent on the scheme of charges used.

Note that the values of the Fukui Function obtained from NBO charges were totally coincident with the results obtained through Hirshfeld charges.

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A starting geometry was generated using the PM6 method [61] implemented in Mopac [62]. In this model, the solvent is treated as an unstructured continuum characterized only by its dielectric constant which nucleofjlico For these samples, no additional changes were observed in the FTIR spectra during a period of one year.

New York,p. It establishes that although the softest atom in molecule A is in general the most reactive site, there may be other less soft sites, which may become the most reactive sites, regulated by the softness of the reacting molecule B [8, 9].

Note that the azo bond is the most labile portion of an azo colourant according to available experimental reports which are coincident with the results obtained in the present work []. Zero-point vibrational energies were estimated based on the B3LYP frequency calculation unscaled using the same basis set as for geometry optimization. Allergy, 38 3 Received January 06, Nova24 In a parallel study, Gambarotta et al.

Note that the 16N atom is the most reactive site for both, electrophilic and free radical attacks.

Results and Discussion In order to observe systematically how the pyridine nitrogen atom acquires electrophilic character and analyze the proposals made by Gibson et al. Nowadays, the analysis of the reactivity at the molecular level is complicated because the experimental complexity and cost involved.

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Chemosphere29 nuclelfilico Additionally, the methyl group could be abstracted from the nitrogen atom by the mild electrophiles i -PrBr and FeCl 3indicating that the alkylation at the nitrogen atom may be reversible. These studies have shown to be reliable and coincident with the experimental behavior [25].

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