Valter H. C. Silva

Morita–Baylis–Hillman Reaction: ESI-MS(/MS) Investigation with Charge Tags and Ionic Liquid Effect Origin Revealed by DFT Calculations

The use of a charge-tagged acrylate derivative bearing an imidazolium tag to study the Morita-Baylis-Hillman reaction via ESI-MS(/MS) monitoring and the effect of such tag (imidazolium cations and ion pairs) over TSs is described. The ionic nature of the substrate was meant to facilitate ESI transfer to the gas phase for direct mass spectrometric analysis. The detection and characterization of charged intermediates has suggested major reaction pathways. DFT calculations considering the effect of a polar and protic solvent (methanol), of a polar and aprotic solvent (acetonitrile), and of no solvent (gas phase) were used to predict possible TSs through a common accepted intermediate. The controversial proton transfer step, which may proceed via Aggarwals or McQuades proposals, was evaluated. Calculations predicted the formation of electrostatic intermediate complexes with both the cation and anion when charge-tagged reagents are used. These complexes contribute to the positive ionic liquid effect, and based on the formation of these unique complexes, a rationale for the ionic liquid effect is proposed. These complexes also pointed to a plausible explanation for the positive ionic liquid effect observed in several reactions that are difficult to be carried out in organic solvents but have shown a beneficial effect when performed in ionic liquids.

Description of the effect of temperature on food systems using the deformed Arrhenius rate law: deviations from linearity in logarithmic plots vs. inverse temperature

In order to account for the deviations from the Arrhenius rate law for the effect of temperature on food processes, we adopt an alternative approach inspired by the deformed exponential based on the Euler limit. The non-enzymatic browning of onions and the growth of bacteria were chosen to validate our proposal, which provides a better description than other formulas previously tested for these systems. These results show that the deformed Arrhenius rate law is suitable for describing the effect of rate-temperature on different food systems and suggest a relationship between the kinetic behavior of food processes and classical collective phenomena.

Structure and theoretical approaches to a chalcone derivative

Chalcones are α,β-unsaturated aromatic ketones which can present a wide range of biological activities. Here, the structure of the chalcone (E)-1-(4-biphenyl)-3-(3,4,5-trimethoxyphenyl)prop-2-en-1-one was determined by single crystal X-ray diffraction technique and compared to those of similar compounds whose crystal structures are available in the Cambridge Structural Database. These comparisons have allowed us to conclude that electron delocalization is abrogated through the biphenyl and carbonyl moieties, while resonance effects are increased through the trimethoxyphenyl group and the olefin carbons. Single-molecule calculations of the asymmetric unit using the DFT method have strengthened these structural relationships, since experimental and theoretical molecular geometries were similar. For instance, the global minimum for the optimized structure occurs when one of the four dihedral angles on the bridge between the two rings of biphenyl is 40.25°, a value close to that of the corresponding torsion determined by single crystal X-ray diffraction analysis [41.7(3)°]. Our theoretical approaches further suggest another stable conformer for different torsions around this bridge, although this conformer was not found in the crystal phase because C–H···π intermolecular interactions contributing to assemble the supramolecular architecture of the studied compound keep only the conformer observed. Other face-to-face π···π stacking interactions and C–H···Ο contacts are also responsible for the crystal assembly.

Fully relativistic rovibrational energies and spectroscopic constants of the lowest {\text{X}}:(1)0_g^{ + } , A′:(1)2u, A:(1)1u, {\text{B}}\prime :(1)0_u^{ - } and {\text{B}}:(1)0_u^{ + } states of molecular chlorine

The main goal of this paper is to present the rovibrational energies and spectroscopic constants of the Cl2 molecular system in the relativistic states

Theoretical investigation of nitric oxide interaction with aluminum phthalocyanine

{\text{X}}:(1)0_g^{ + }

Uniform description of non-Arrhenius temperature dependence of reaction rates, and a heuristic criterion for quantum tunneling vs classical non-extensive distribution

, A′:(1)2u, A:(1)1u,

Stereodirectional Origin of anti-Arrhenius Kinetics for a Tetraatomic Hydrogen Exchange Reaction: Born–Oppenheimer Molecular Dynamics for OH + HBr

{\text{B}}\prime :(1)0_u^{ - }