Barbara C. Fiorin

Theoretical and experimental investigation on the rotational isomerism in alpha-fluoroacetophenones.

The geometries involved in the conformational equilibria of alpha-fluoroacetophenone, p-nitro-alpha-fluoroacetophenone, and p-methoxy-alpha-fluoroacetophenone were investigated. Theoretical calculations showed that cis and gauche forms (F-C-C=O) are their most stable conformers and that in the vapor phase the gauche conformer is predominant. The three compounds were synthesized, and the conformational behavior in solution was estimated from infrared (IR) and nuclear magnetic resonance (NMR) spectra obtained in solvents of different polarity. Their IR spectra showed one carbonyl absorption for the cis and one for the gauche conformer, and that the cis conformer was preferred in the more polar solvents. (1)J(CF), (2)J(C(O)F), and (2)J(HF) coupling constants were obtained from their NMR spectra, and they also showed a preference for the cis conformer when more polar solvents were used. The vapor phase calculations showed a conformational preference for the gauche form. However, when the solvent effects were included in the calculations, the results were in complete agreement with the experimental data (NMR and IR), the cis conformer being the most stable one.

Rotational isomerism of some chloroacetamides: Theoretical and experimental studies through calculations, infrared and NMR

The geometries involved in the conformational equilibria of 2,2-dichloro-N-cyclohexyl-N-methyl-acetamide (DCCMA) and 2-chloro-N,N-dicyclohexylacetamide (CDCA) were investigated. Theoretical calculations at the B3LYP/cc-pVDZ level of theory showed that gauche forms (ClCCO) are the most stable and the predominant conformers in isolated phase. Both compounds had the conformational behavior in solvents of different polarities estimated from theoretical calculations with the PCM (Polarizable Continuum Model), at the same level of theory, using infrared data from deconvolution of the carbonyl absorption bands and (13)C NMR spectra. Their IR spectra showed two carbonyl absorptions and that the conformer with the highest dipole moment had its population increased when the most polar solvents were used, in accordance with the theoretical calculation in solution. (1)JCH coupling constants were obtained from their NMR spectra, and revealed that there was population variation of conformers with solvent exchange. Experimental data (NMR and IR) as well as calculations including the solvent effects followed the same trend.

Sol gel synthesis of 3- n -propyl(4-aminomethyl)pyridinium silsesquioxane chloride and the enhanced electrocatalytic activity of LbL films

AbstractA silsesquioxane based on a silica matrix and 4-(aminomethyl)pyridine group was successfully synthesized using the sol–gel process with the proposal of two different carbonic chain arrangments in the structure of the silica polymer, observed employing NMR techniques. The silsesquioxane proposed succeeds an improvement of the adsorption of monomer electroactive species on the surface of the electrode obtained through films assembly, this fact was attributed to the presence of two coordinating nitrogen in new silsesquioxane. In this study, the Layer-by-Layer (LbL) technique was shown suitable to be used to produce electroactive electrodes with indium tin oxide electrode (ITO) coated by tetrasulfonated nickel phthalocyanine (NiTsPc) alternated with the silsesquioxane. Voltammetric techniques were used to investigate the electrochemical behavior of the nitrite oxidation, which exhibited an enhanced current response at the modified electrode. The proposed electroddisplayed a current response which varied linearly with the concentration of nitrite in the range 0.113 to 0.860 mmol L−1 with a detection limit of 0.026 mmol L−1, a sensitivity of 32.06 µA (mmol L−1) and relative standard deviation of approximately 3%. HighlightsSynthesis of hybrid containing both ammoniummethyl pyridine and aminomethyl pyridinium groups.The new material allows a greater adsorption of metal phthalocyanine monomers.The electrode obtained allows the detection of 0.026 mmol L−1 nitrite.