SOLVENT EFFECTS OF KINETICS OF [1,5] H-SHIFT IN CYCLOPENTADIENE AND ITS DERIVATIVES

2005 ◽  
Vol 04 (01) ◽  
pp. 151-161 ◽  
Author(s):  
VUDHICHAI PARASUK ◽  
SAKULSUK UNARUNOTAI
Keyword(s):  
Solvent Effects ◽  
Single Point ◽  
Solvent Polarity ◽  
Polarizable Continuum Model ◽  
Activation Energies ◽  
Free Energies ◽  
Solvent Systems ◽  
Polarizable Continuum ◽  
Kinetics Of ◽  
Fluoro Derivatives

Geometries of reactants, products (in the case of fluoro derivatives), and transition states in gas and solution phases of [1,5] H-shift of cyclopentadiene and 2-fluorocyclo-pentadiene were optimized using B3LYP/6-31++G(d,p) . The solvent effects were included using the Polarizable Continuum Model (PCM). Four solvent systems i.e. chloroform, dichloromethane, diethylether, and methanol, were considered. For cyclopentadiene, single point MP2/6-31++G(d,p) were also carried out. For cyclopentadiene and 2-fluorocyclopentadiene, using B3LYP/6-31++G(d,p) activation free energies of 25.47 and 28.74 kcal/mol respectively were yielded for the reaction in vacuum. In solutions, calculated activation energies for the reaction are slightly decreased with the reduction of around 0.5–3 kcal/mol depending on solvent. Good correlation between the solvent polarity and activation energies was also observed. Thus, the [1.5] H-shift in cyclopentadiene and its derivatives could be enhanced in polar solvents.

Solvent and temperature effects on the tautomerization of a carbonitrile molecule: A conductor-like polarizable continuum model (CPCM) study

2021 ◽  
Vol 20 (1) ◽  
pp. 59-68
Author(s):  
Zohreh Khanjari ◽  
Bita Mohtat ◽  
Reza Ghiasi ◽  
Hoorieh Djahaniani ◽  
Farahnaz Kargar Behbahani
Keyword(s):  
Gas Phase ◽  
Solvent Effects ◽  
Continuum Model ◽  
Solvent Polarity ◽  
Polarizable Continuum Model ◽  
Dielectric Constants ◽  
Frontier Orbitals ◽  
Reaction Field ◽  
Polarizable Continuum ◽  
Homo Lumo

This research examined the effects of solvent polarity and temperature on the tautomerization of a carbonitrile molecule at CAM-B3LYP/6-311G (d,p) level of theory. The selected solvents were n-hexane, diethyl ether, pyridine, ethanol, methanol, and water. The solvent effects were examined by the self-consistent reaction field theory (SCRF) based on conductor-like polarizable continuum model (CPCM). The solvent effects were explored on the energy barrier, frontier orbitals energies, and HOMO-LUMO gap. Dependencies of thermodynamic parameters (ΔG and ΔH) on the dielectric constants of solvents were also tested. Specifically, the temperature dependencies of the thermodynamics parameters were studied within 100–1000 K range. The rate constant of the tautomerism reaction was computed from 300 to 1200 K, in the gas phase.

THEORETICAL CALCULATION OF pKb VALUES FOR ANILINES AND SULFONAMIDE DRUGS IN AQUEOUS SOLUTION

2012 ◽  
Vol 11 (02) ◽  
pp. 283-295 ◽  
Author(s):  
BAHRAM GHALAMI-CHOOBAR ◽  
ALI GHIAMI-SHOMAMI ◽  
PARIA NIKPARSA
Keyword(s):  
Gas Phase ◽  
Continuum Model ◽  
Correlation Equation ◽  
Polarizable Continuum Model ◽  
Free Energies ◽  
Pcm Model ◽  
Solvation Models ◽  
Polarizable Continuum ◽  
Better Than ◽  
Good Agreement

In this work, calculations of p K b values have been performed for aniline and its substituted derivatives and sulfonamide drugs by using Gaussian 98 software package. Gas-phase energies were calculated with HF /6-31 G ** and B3LYP /6-31 G ** levels of theory. Free energies of solvation have been computed using the polarizable continuum model (PCM), conductor-like polarizable continuum model (CPCM) and the integral equation formalism-polarizable continuum model (IEFPCM) at the same levels which have been used for geometry determination in the gas-phase. The results show that the calculated p K b values using the B3LYP /6-31 G ** are better than those using the corresponding HF /6-31 G **. At first, the correlation equation was found to determine the p K b values of the investigated anilines. Then, this correlation equation was used to calculate the p K b values of the sulfonamide drugs. The results obtained indicate that the PCM model is a suitable solvation model for calculating p K b values in comparison to the other solvation models. For the investigated compounds a good agreement between the experimental and the calculated p K b values was also observed.

THE ALKALINE CLEAVAGE OF o-NITROBENZYLTRIMETHYLSILANE SOLVENT EFFECTS IN THE DIOXANE–WATER SYSTEM

1963 ◽  
Vol 41 (6) ◽  
pp. 1525-1530 ◽  
Author(s):  
H. R. Allcock
Keyword(s):  
Transition State ◽  
Solvent Effects ◽  
Water System ◽  
Solvent Polarity ◽  
High Water ◽  
Aqueous Dioxane ◽  
Alkaline Cleavage ◽  
Rate Of Reaction ◽  
Kinetics Of

The kinetics of alkaline cleavage of o-nitrobenzyltrimethylsilane were examined in aqueous dioxane media. At high water concentrations, increases in solvent polarity retard the cleavage, as required by a mechanism involving charge dispersion in the transition state. At high dioxane concentrations, solvent polarity increases are accompanied by increases in the rate of reaction, a result which may reflect association between the solvent components.

Polarizable Continuum Model (PCM) Calculations of Solvent Effects on Optical Rotations of Chiral Molecules

2002 ◽  
Vol 106 (25) ◽  
pp. 6102-6113 ◽  
Author(s):  
B. Mennucci ◽  
J. Tomasi ◽  
R. Cammi ◽  
J. R. Cheeseman ◽  
M. J. Frisch ◽  
...  
Keyword(s):  
Solvent Effects ◽  
Continuum Model ◽  
Polarizable Continuum Model ◽  
Chiral Molecules ◽  
Optical Rotations ◽  
Polarizable Continuum

scholarly journals Solvation environment effects on the photoisomerization equilibrium of the model tannins catechin and epicatechin as natural sunscreens in aquatic systems

2016 ◽  
Vol 94 (10) ◽  
pp. 865-869 ◽  
Author(s):  
Sierra Rayne ◽  
Kaya Forest
Keyword(s):  
Density Functional ◽  
Solvent Polarity ◽  
Polarizable Continuum Model ◽  
Aquatic Systems ◽  
Substantial Variation ◽  
Solvation Model ◽  
Structural Framework ◽  
Environment Effects ◽  
Isomerization Energy ◽  
Polarizable Continuum

The photoisomerization equilibrium between the model tannins (-)-catechin and (-)-epicatechin in aqueous solution was investigated at the density functional level of theory to gain insights into the action of these compounds as natural sunscreens in aquatic systems. Increasing water temperature, as might be expected on seasonal and diurnal bases, is predicted to shift the equilibrium further in favor of catechin. The isomerization energy between catechin and epicatechin was also considered in a range of polar protic, polar aprotic, apolar protic, and apolar aprotic solvents using the solvation model based on density (SMD) and integral equation formalism polarizable continuum model (IEFPCM). The IEFPCM yielded a modest range in isomerization energies depending on solvent polarity or proticity, whereas a substantial variation was observed with the SMD. The SMD results suggest that the solvation environment around catechin and epicatechin will play a major role on the photoisomerization equilibrium between these two compounds. As the freely dissolved monomer in aquatic systems, the catechin–epicatechin photoisomerization equilibrium will be in the range of 11:1 to 14:1. In the less polar environments of associations with dissolved organic matter or within a larger tannin structural framework, the theoretical modeling efforts indicate that the catechin–epicatechin photoisomerization equilibrium could be as low as 3:1.

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