Structures and Vibrational Spectra of CH,OCH,CH,OH : The

Ab initio calculations at the MP2/6-31G* and MP2/6-31G*//6-31G* levels have been carried out for the monomer of 2-methoxyethanol (CH,OCH,CH,OH). The MP2/6-31G* results indicate that the two more stable conformers (tGg’ and gGg‘) display intramolecular hydrogen bonds directed from the hydroxy H atom to one of the lone pairs of the ether 0 atom, and that the tGg’ conformer is 6.3 kJ mol-’ more stable than the gGg’ conformer. As the MP2/6-31G* and MP2/6-3lG*//6-31G* calculations do not yield results differing by more than a few tenths of a kJ mol-‘, it is concluded that the structure-sensitive and the dynamic correlation corrections are far from being additive. While the optimization of geometry for the correlated wavefunction generally leads to increase of bond lengths and reduction of bond angles, on the whole the geometrical parameters undergo similar changes in different conformers. Ab initio harmonic 6-31G* derived force fields were used to perform normal mode analyses for the more stable conformers. The calculated v(CH) frequencies are found to correlate linearly with some of the ab initio calculated CH bond lengths. An interpretation of the FTIR and Raman spectra for the liquid phase consonant with the structural and vibrational ab initio results is presented. Two spectral features observed both in Raman and in FTIR spectra and associated with v(0H) in monomeric species are ascribed to conformers, in accord with the theoretical and experimental results. On the whole, both the structural and the vibrational results presented point to a distinction between the hydrogen-bonded G-type conformers (tGg’ and gGg‘) and the higher energy T-type conformers (tTg and tTt)

Estimativa de parâmetros biofísicos no bioma Cerrado do Estado de Minas Gerais.

Natural habitats decrease in extension and integrity may be considered as an indicator of biodiversity decay. Land-use and land-cover changes (LULCC), original ecosystems conversion to other anthropic uses, have direct effects on biodiversity and climate. The Cerrado biome extends over approximately 2,000,000 km2 and between 2002 and 2013 nearly 126,000 km² of its natural plant cover was suppressed (-10.7%), 11.4 thousand km² year-1. The Simple Algorithm for Evapotranspiration Retrieving (SAFER) is an agrometeorological spectral model for estimating large-scale biophysical parameters using satellite images and climate data interpolated from meteorological stations. SAFER does not require the use of the thermal band. The SAFER model was used to estimate biophysical parameters in anthropic and natural land-use classes in a portion of the Brazilian state of Minas Gerais which is covered by Cerrado vegetation. Our results show "silviculture" as the anthropic land-use class with the highest biomass (146 kg ha-1 day-1) and ET (3.3 mm day-1) values. Among the natural plant-cover classes, the highest values were estimated for "forest" (85.8 kg ha-1 day-1 and 2.4 mm day-1). We recommend that future studies apply the SAFER model to medium spatial resolution images (e.g. Landsat-8, Sentinel-2) with the aim of estimating parameters in a more detailed scale

Hydrogen-Bonded Dimers of CH3OCH2CH2OH: Ab Initio Structures and Multivariate Analysis

Structures and vibrational frequencies of relevant hydrogen-bonded dimers of 2-methoxyethanol are obtained at the 3-21G*//Ah41 level (the 3-21G* basis set included polarization functions deliberately added to second period atoms) and the results analyzed by standard multivariate methods. Dimers built from the same pair of isolated monomers belong to the same homologous series. The most stable dimer is obtained from the most stable conformations of both monomers, has a 10-membered intermolecular ring with a boat-chairboat conformation, and presents a zero dipole moment. In addition, the most stable dimers of the three homologous series have 10-membered rings with relatively symmetric conformations and zero or very low dipole moments. The energies of the monomers in these dimers-monomers with geometries frozen in the dimer-are close to the isolated and relaxed monomers energies. Generally speaking, OH 0 and CH 0 hydrogen bonds are found to contribute appreciably for the stability of the dimers. In particular, for the second most stable dimer, two of the three CH -0 hydrogen bonds are shorter than the intramolecular OH- 0 bond for the isolated monomer. Multivariate analysis of all the results shows that the 0. *H-0 angle is highly correlated with the H-0 bond length and that the COC and OCC angles are also highly correlated for both monomers, hence confirming that each monomer in a dimer keeps essentially the same conformation it has in the isolated monomer. The first and second principal components include all the highly correlated variables and account for 45% of the total variance. 3-D plots of the three most important principal components confirm a strong structural resemblance both for 10-membered ring dimers of homomeric series, Le., formed by the same monomers, and for the more stable dimers in each homologous series. In addition, among the heteromeric dimers with seven membered rings, the ones whose first conformation is G or G’ are less stable and located in a separate group

Evapotranspiração de referência para dimensionamento de sistemas de irrigação em Petrolina, PE.

A evapotranspiração é uma variável fundamental para estimar a exigência hídrica das culturas, e também fornece subsídio para o dimensionamento de sistemas de bombeamento, adução e distribuição de água na irrigação. A caracterização da distribuição de frequência da evapotranspiração de referência (ETo), estimada pelo método do tanque classe ?A? em Petrolina - PE, foi realizada com base em série histórica de dados de 1963 a 2010, os quais foram agrupados em períodos de 5, 10, 15 e 30 dias. As distribuições gama e normal foram aplicadas aos dados de ETo com probabilidade de 95, 90, 75, 50, 25, 10 e 5%, e foram aptas para representar os dados de evapotranspiração de referência para os períodos acumulados de 10, 15 e 30 dias. Os valores de ETo (11,06 e 11,07 mm dia-1, distribuição gama e normal, respectivamente) para o mês de outubro no período acumulado de 15 dias com probabilidade de 75%, foram os mais indicados para o dimensionamento da lâmina diária máxima de projetos de sistemas de irrigação

Avaliação físico-química de híbridos de melancia sem sementes.

Suplemento. Edição dos Anais do 52 Congresso Brasileiro de Olericultura, Salvador, jul. 2012

Desempenho agronômico de genótipos de melancia sob diferentes ambientes de cultivo.

Suplemento. Edição dos Anais do 52 Congresso Brasileiro de Olericultura, Salvador, jul. 2012