Vibrational and thermal studies of essential oils derived from Cistus ladanifer and Erica arborea shrubs

Producción CientíficaEssential oils from the two most representative shrub species from the Iberian Peninsula (namely Cistus ladanifer L. and Erica arborea L.) have been characterized by Fourier transform infrared spectroscopy (FTIR) and thermoanalytical techniques (TG/DTG and DSC). Vibrational spectra have been compared with those of components of the plants, and with those of oils, gums and resins from other species. The different content in terpenoids of C. ladanifer oil (mainly mono- and sesquiterpenoids) and E. arborea oil (mainly triterpenoids) is reflected in the ATR-FTIR by the position of the bands at around 2873 cm−1, 1730 cm−1 and 1678 cm−1. As regards their thermal behavior, C. ladanifer-derived oil evinced higher thermal stability than that of obtained from E. arborea: the pyrolysis of the former was sensitized at 210°C, whereas for the later it occurred at 143°C. These temperatures are high enough to state that thermolabile constituents such as terpenoids are conserved in the hydrodistillation and that this extraction process ensures the recovery of the main constituents of both essential oils.Programa LIFE+ de la Unión Europea (Proyecto LIFE11 ENV/ ES/000535)Fundação para a Ciência e a Tecnologia (FCT) (Proyecto UID/QUI/UI0313/2013

Interpretação das propriedades volumétricas e de viscosidade de soluções de não-electrólitos. Coimbra, ed. aut., 1995, 140 p.

O trabalho apresentado nesta dissertação é uma contribuição para a interpretação de propriedades termodinâmicas e de transporte de soluções de não-electrólitos. Estudaram-se duas propriedades: uma termodinâmica, o volume molar parcial, e uma de transporte, a viscosidade. Na interpretação do volume molar parcial recorreu-se à Mecânica Estatística por forma a separar a contribuição devida à interacção soluto/solvente da contribuição intrínseca à molécula do soluto. A interpretação molecular da viscosidade foi efectuada a partir do coeficiente B de Jones e Dole e das funções termodinâmicas de activação de escoamento viscoso. Escolheram-se como solutos compostos hidroxilados cujas moléculas diferem tanto na relação parte polar/parte apolar, como na posição relativa dos grupos hidroxilo. Como solventes usaram-se líquidos polares práticos - água e formamida - e líquidos polares apróticos - dimetilsulfóxido e carbonato de propileno. Com este grupo de solutos e de solventes é possível simular um conjunto variado de situações por forma a esclarecer o tipo de informações sobre a interacção soluto/solvente que é possível retirar das propriedades estudadas. O método de estudo seguido permitiu quantificar o volume de interacção do grupo hidroxilo com os vários solventes estudados. A interacção deste grupo com a água tem um reflexo global no coeficiente B de Jones e Dole negativo, ao contrário do que se verifica nos solventes polares apróticos. Este facto põe em evidência a incompatibilidade entre a orientação da ligação de hidrogénio soluto/solvente e a estrutura própria da água. A viscosidade, ao contrário do volume molar parcial, permite concluir também quanto à interacção de grupos apolares com os solventes. A interacção grupo apolar/solvente dá lugar a uma contribuição pouco significativa para B nos solventes polares apróticos. No caso do solvente ser a água esta contribuição é positiva

Molecular structure, infrared spectra, photochemistry, and thermal properties of 1-methylhydantoin

The structural, vibrational, and photochemical study of 1-methylhydantoin (1-MH, C4H6N2O2) was undertaken by matrix isolation infrared spectroscopy (in argon matrix; 10 K), complemented by quantum chemical calculations performed at the DFT(B3LYP)/6-311++G(d,p) level of approximation. The theoretical calculations yielded the Cs symmetry structure, with planar heavy atom skeleton, as the minimum energy structure on the potential energy surface of the molecule. The electronic structure of this minimum energy structure of 1-MH was then studied in detail by means of the natural bond orbital (NBO) and atoms in molecules (AIM) approaches, allowing for the elucidation of specific characteristics of the molecule's σ and π electronic systems. The infrared spectrum of the matrix-isolated 1-MH was fully assigned, also with the help of the theoretically predicted spectrum of the compound, and its UV-induced unimolecular photochemistry (λ ≥ 230 nm) was investigated. The compound was found to fragment to CO, isocyanic acid, methylenimine, and N-methyl-methylenimine. Finally, a thermal behavior investigation on 1-MH samples was carried out using infrared spectroscopy (10 K until melting), differential scanning calorimetry and polarized light thermal microscopy. A new polymorph of 1-MH was identified. The IR spectra of the different observed phases were recorded and interpreted

2,4,6-Trinitro-N-(m-tolyl)aniline: A New Polymorphic Material Exhibiting Different Colors

2,4,6-Trinitro-N-(m-tolyl)aniline or N-picryl-m-toluidine (abbreviated as TMA), exhibiting color polymorphism, was synthesized and characterized structurally, spectroscopically and thermodynamically. The studies consider both the isolated molecule of the compound (studied theoretically at the DFT(B3LYP)/6-311++G(d,p) level, and experimentally by matrix isolation infrared spectroscopy) and its polymorphic crystalline phases. The investigations on the isolated molecule allowed to evaluate the major intramolecular interactions determining the conformational preferences of the compound, and characterize it in detail from the vibrational point of view. Two conformers were found (A and B), which differ in the relative orientation of the ring moieties of the molecule. Polymorph screening, by recrystallization of the compound using different solvents, allowed to identify three different polymorphs, exhibiting red, orange and yellow colors, which were subsequently characterized structurally by single crystal X-ray diffraction, vibrationally, by infrared and Raman spectroscopies (complemented by fully-periodic DFT calculations on the crystals), electronically, using solid state ultraviolet-visible absorption spectroscopy, and thermodynamically, by differential scanning calorimetry and polarized light thermomicroscopy. The yellow polymorph was found to be a conformational polymorph of the orange and red ones, while the last two are packing polymorphs. Mechanistic insights on the causes of the different colors of the polymorphs are presented. On the whole, the reported investigation constitutes a comprehensive structural (for both the isolated molecule and crystalline phases), spectroscopic and thermal analysis of the newly prepared compound, with particular emphasis on the rare color polymorphism it exhibits