Edilson Clemente da Silva

Ozonolysis of Geraniol-trans, 6-Methyl-5-hepten-2-one, and 6-Hydroxy-4-methyl-4-hexenal: Kinetics and Mechanisms

A combined density functional theory and transition-state theory study of the mechanisms and reaction coefficients of gas-phase ozonolysis of geraniol-trans, 6-methyl-5-hepten-2-one, and 6-hydroxy-4-methyl-4-hexenal is presented. The geometries, energies, and harmonic vibrational frequencies of each stationary point were determined by B3LYP/6-31(d,p), MPW1K/cc-pVDZ, and BH&HLYP/cc-pVDZ methods. According to the calculations, the ozone 6-methyl-5-hepten-2-one reaction is faster than the ozone 6-hydroxy-4-methyl-4-hexenal reaction, but both are slower than the ozone geraniol-trans reaction. By using the BH&HLYP/cc-pVDZ data, a global rate coefficient of 5.9 x 10(-16) cm(3) molecule(-1) s(-1) was calculated, corresponding to the sum of geraniol-trans, 6-methyl-5-hepten-2-one, and 6-hydroxy-4-methyl-4-hexenal reactions with the ozone. These results are in good agreement with the experimental studies.

Theoretical Investigation on the Stability of Ionic Formic Acid Clusters

Recent experimental results on positive charged formic acid clusters generated by the impact of (252)Cf fission fragments (FF) on icy formic acid target are examined in this paper by quantum mechanical calculations. Structures for the clusters series, (HCOOH)(n)H(+) and (HCOOH)(n)H(3)O(+), where 2 < or = n < or = 4, are proposed based on ab initio electronic structure methods. Results show that cluster growth does not present a regular pattern of nucleation. A stability analysis was performed considering the commonly defined stability function, where E is the total electronic energy plus the zero point vibrational energy correction, including the BSSE correction. The stability analysis leads to a picture that is compatible with experimental observations, indicating a decay of the stability with the increase of cluster mass. Temporal behavior of the clusters was evaluated by Born-Oppenheimer molecular dynamics to check the mechanism that provides cluster stability. The evaluated temporal profiles indicate the importance of hydrogen atom migration between the formic acid moieties to maintain the stability of the structures.

Carbonyl oxides reactions from geraniol-trans-(3,7-dimethylocta-2,6-dien-1-ol), 6-methyl-5-hepten-2-one, and 6-hydroxy-4-methyl-4-hexenal ozonolysis: kinetics and mechanisms.

A density functional theory (DFT) study of the mechanisms of carbonyl oxide reactions from geraniol-trans, 6-methyl-5-hepten-2-one, and 6-hydroxy-4-methyl-4-hexenal ozonolysis is presented. The geometries, energies, and harmonic vibrational frequencies of each stationary point were determined by B3LYP/6-31(d,p) and BH&HLYP/cc-pVDZ methods. According to the calculations, the ozonolysis reactions are initiated by the formation of van der Waals (VDW) complexes to yield primary ozonides, which rapidly open to carbonyl oxide compounds. These carbonyl oxide compounds react to form dioxanes and hydroperoxides. The hydroperoxides react by isomerization to form stable products. Glyoxal and methyl-glyoxal have been identified as the final product from geraniol-trans, 6-methyl-5-hepten-2-one, and 6-hydroxy-4-methyl-4-hexenal ozonolysis. Our results are in good agreement with the experimental studies.

Theoretical determination of the theta temperature for solvent–polymer systems

Abstract The miscibility behavior of five binary polymer–solvent systems was studied by means of the Flory–Huggins theory. The theta temperature and the entropic and energetic Flory–Huggins parameters were calculated for these systems. The coordination number in the Flory–Huggins model and the interaction energy parameters were determined using a molecular simulation technique based on a Monte Carlo approach, which takes into account the constraints associated with excluded volume. In all cases, the critical temperature (Tc) values were calculated and compared with the experimental data. Thermodynamic parameters were obtained by plotting 1/Tc versus 1/x 2 1 2 +1/2x 2 curve, where x2 is the degree of polymerization. This study shows a further application of the Flory–Huggins theory combined with molecular simulation techniques, for the model parameter determination, which was previously proposed by C.F. Fan, B.D. Olafson, M. Blanco, Macromolecules 25 (1992) 3667 [1] . In addition, the limitations of the methodology proposed by C.F. Fan, B.D. Olafson, M. Blanco, Macromolecules 25 (1992) 3667 [1] , for miscibility calculations of binary polymer systems, are further discussed with special attention given for the model parameter determination.

Theoretical study of the addition of OH radicals to trans-geraniol-(3,7-dimethylocta-2,6-dien-1-ol), 6-methyl-5-hepten-2-one, and 6-hydroxy-4-methyl-4-hexenal.

A combined density functional theory and transition state theory study of the gas-phase addition of OH to 3,7-dimethylocta-2,6-dien-1-ol (trans-geraniol), 6-methyl-5-hepten-2-one, and 6-hydroxy-4-methyl-4-hexenal is presented. In this study, all different possibilities for the addition of the OH radical to the C-C double bonds in trans-geraniol, 6-methyl-5-hepten-2-one, and 6-hydroxy-4-methyl-4-hexenal were considered. The geometries, energies, and harmonic vibrational frequencies at each stationary point were determined at the MPW1K/cc-pVDZ and BH&HLYP/cc-pVDZ levels. Global rate coefficients of 0.94 x 10(-10) and 3.1 x 10(-10) cm(3) molecule(-1) s(-1), 2.11 x 10(-11) and 7.53 x 10(-11) cm(3) molecule(-1) s(-1), and 2.70 x 10(-13), and 4.37 x 10(-12) cm(3) molecule(-1) s(-1) were calculated using data obtained at the BH&HLYP/cc-pVDZ and MPW1K/cc-pVDZ levels of theory. These coefficients correspond to the sum of the rate coefficients of the individual paths for trans-geraniol, 6-hydroxy-4-methyl-4-hexenal, and 6-methyl-5-hepten-2-one, when reacting with OH radicals. The calculated rate coefficients are in good agreement with the available experimental data.