Vanessa E. de Oliveira

OXOCARBONOS, PSEUDO-OXOCARBONOS E ESQUARAÍNAS

Oxocarbons ions are cyclic compounds presenting unusual electronic and vibrational properties. These molecules anions possess a high symmetry and degree of electronic delocalization, characteristics that have been discussed in several structural and spectroscopic investigations. Compounds in which one or more of the carbonyl oxygen atoms are replaced by other atoms or groups are called pseudo-oxocarbons. Compounds formed by substitution of the carbonyl groups by nitrogen groups former a new class named squaraines. Specificity the dicyanomethylene groups are interesting because of the possibility of further extension of the electronic delocalization and a new coordination site. These molecules also present interesting coordination properties which make these systems potentially useful in crystal engineering research.

Oxocarbons, pseudo-oxocarbons and squaraines

Oxocarbons ions are cyclic compounds presenting unusual electronic and vibrational properties. These molecules anions possess a high symmetry and degree of electronic delocalization, characteristics that have been discussed in several structural and spectroscopic investigations. Compounds in which one or more of the carbonyl oxygen atoms are replaced by other atoms or groups are called pseudo-oxocarbons. Compounds formed by substitution of the carbonyl groups by nitrogen groups former a new class named squaraines. Specificity the dicyanomethylene groups are interesting because of the possibility of further extension of the electronic delocalization and a new coordination site. These molecules also present interesting coordination properties which make these systems potentially useful in crystal engineering research.

Raman Spectroscopic Investigation of Carotenoids in Oils from Amazonian Products

ABSTRACT In this work several different natural products from the Amazon forest were analyzed by means of Raman spectroscopy, using the 1064-nm laser line as a way to obtain the spectra. All the oil samples from handmade produced buriti, babaçu, and pequi, as well as the refined andiroba, cold-pressed passion flower, and palm oils, were acquired in the local market in Brazil. Some products present in all the spectra of the ν(C˭C) vibration, observed in the 1525 cm−1 region, the ν(C-C) mode near 1158 cm−1, and the ρ(C-CH3) mode near 1008 cm−1, can be seen; all these bands are assigned generally to the presence of a C9 carotenoid and can be more precisely attributed to the ν1, ν2, and δ modes of β-carotene. Also, the characteristic Raman scattering bands common to all the oils arising from vibrations of the hydrocarbon chains can be observed, namely, aromatic ring C˭C stretching at 1658 cm−1 (ν(C˭C)); CH2 scissoring deformation at 1439 cm−1 (δ(CH2); vibrations of in-phase methylene twisting at 1301 cm−1, and symmetric CH rocking in unconjugated cis-double bonds at 1270 cm−1 (δ(C–H)), as well as C˭O stretching from the ester groups at 1747 cm−1 [ν(C˭O)]. It is noteworthy that most natural oils have a major contribution of components of some of the main fatty acids: palmitic (C16), oleic (C18:1), and linoleic (C18:2), and no carotenoid was detected in the Raman spectra of the white babaçu oil or in the pale yellow andiroba oil. As a major conclusion, direct Raman spectroscopic measurements using a near-infrared wavelength as the excitation source can be used as a primary test to monitor the quality control of natural oils extracted from the Amazon forest, namely, andiroba, burity, babaçu, and pequi oils.

Squaraines: crystal structures and spectroscopic analysis of hydrated and anhydrous forms of squaric acid-isoniazid species.

The crystal structures, synthesis procedure, thermal behavior, and spectroscopic properties of a new squaraine SqINH·H2O and its anhydrous arrangement are described. This squaraine is obtained through an acid-base reaction using squaric acid (H2Sq) and isoniazid (INH) as precursors. Both squaraines crystallize in the monoclinic system, but in different space groups: the hydrated and anhydrous arrangement crystallizes in the P2₁ and P2₁/c space group, respectively. The crystallographic data strongly suggest that the structures present an expressive increase in their electronic delocalization all over the molecular structure of both compounds, when compared with the reagents. The bond distances for both structures present an average value intermediate between a single and double character (1.463(3) Å for SqINH·H2O and 1.4959(3) Å for SqINH). The vibrational and electronic data also corroborate with this proposal, since the band shifts indicate that the conjugation over the system is increased, as indicated by the blue shift observed for the carbonyl stretching bands for both compounds. The presence of the water molecule is responsible for a decrease in fluorescence emission, as determined by the emission spectra recorded for both compounds.

Ammonium dicyano­(cyano­acet­yl)methanide: one condensation product of malononitrile

The title compound, NH4+·C6H2N3O−, was obtained as a secondary product in a reaction of squaric acid and excess malononitrile (1:20). The crystal packing displays a wave-like arrangement of molecules parallel to b, in which anion layers are linked by medium–weak hydrogen bonds to the ammonium cation, giving rise to a three-dimensional network. The average N⋯O and N⋯N distances are 2.843 (2) and 3.025 (3) A, respectively.