A Theoretical Study of Silanol Polymerization

1986 ◽  
Vol 73 ◽  
Author(s):  
Larry W. Burggraf ◽  
Larry P. Davis
Keyword(s):  
Complex Systems ◽  
Molecular Orbital ◽  
Anionic Polymerization ◽  
Theoretical Study ◽  
State Of The Art ◽  
Activation Barrier ◽  
Polymerization Process ◽  
Nucleophilic Attack ◽  
Semi Empirical ◽  
Coordinate Structures

ABSTRACTWe have applied state-of-the-art semi-empirical molecular orbital methods to a study of the anionic polymerization of silanols to form silica. In particular, we have considered nucleophilic attack on silanols and subsequent reactions of the products. Hydroxide addition proceeds without activation to form five-coordinate silicate anions. Five-coordinate structures can also be formed by oligomerization following the attack of hydroxide on neutral silanols to abstract a proton. These five-coordinate structures are predicted to play a key role as intermediates in the polymerization process. Water can be eliminated from these anions, but with a substantial activation barrier. The activation barrier appears to be lower for the larger, more complex systems. These predictions are consistent with a rapid pre-equilibrium to form dimer anions followed by the slower reaction to form higher oligomers.

Theoretical study on the diffusion of gases in hexagonal ice by the molecular orbital method

2003 ◽  
Vol 81 (1-2) ◽  
pp. 251-259 ◽  
Author(s):  
A Hori ◽  
T Hondoh
Keyword(s):  
Molecular Orbital ◽  
Lower Energy ◽  
Theoretical Study ◽  
Orbital Method ◽  
Molecular Orbital Method ◽  
Hexagonal Ice ◽  
Diffusion Constants ◽  
Ice Lattice ◽  
Semi Empirical ◽  
Good Agreement

To estimate the diffusion constants for various gases in ice, the barrier energies during interstitial diffusion are calculated for model ice clusters by the molecular orbital method. For He and Ne, the calculated values for diffusion along the c-axis were 0.11 and 0.26 eV, respectively. These are in good agreement with the experimental results. However, the calculated values for the diffusion of He perpendicular to the c-axis are not in close agreement with the experimental data. The barrier energies for O2, N2, and CH4 were calculated by the semi-empirical molecular orbital method and estimated to be 0.35, 0.47, and 0.75 eV, respectively. The lower energy for O2 in comparison with N2 is attributed to the formation of a quasi chemical bond between the O2 molecule and the ice lattice. The diffusion constants for O2, N2, and CH4 were estimated to be 1.8 x 10–11, 2.5 x 10–12, and 2.0 x 10–14 m2s–1, respectively. PACS Nos.: 31.15Ar, 31.15Ne, 66.30Jt, 66.30Ny

scholarly journals Theoretical Study of The Chemical Reactivity of A Class of Trivalent Phosphorus Derivatives Towards Polyhaloalkanes: DFT Study.

2021 ◽  
Author(s):  
Ali Barhoumi ◽  
Mohammed El idrissi ◽  
Abdellah Zeroual ◽  
Abdessamad Tounsi ◽  
Salam Bakkas ◽  
...  
Keyword(s):  
Theoretical Study ◽  
Activation Barrier ◽  
Chemical Reactivity ◽  
Nucleophilic Attack ◽  
Trivalent Phosphorus ◽  
Reactivity Indices ◽  
Theoretical Predictions ◽  
The One ◽  
Good Agreement

Abstract In the current work, the chemical reactivity of some trivalent phosphorus derivatives R2PR' towards polyhaloalkanes CCI3POR''2 was studied by the quantum method DFT/B3LYP/6-311G (d,p). The introduction of substituents for the trivalent phosphorus derivative and polyhaloalkane allowed us to have more information on these reactions. On the one hand, the calculation of reactivity indices derived from the DFT/B3LYP/6-311G(d,p) method and the gapLUMO-HOMO show that trivalent organophosphorus derivatives behave as nucleophiles, while polyhaloalkanes act as electrophiles. On the other hand, the calculation of the activation barrier and the determination of the free enthalpy variation prove that the kinetic and thermodynamic products of these reactions result from the nucleophilic attack of the phosphorus atom on the chlorine halogen. All these theoretical predictions are in very good agreement with the experimental results.

A semi-empirical molecular orbital scheme to study electron transfer in iron–sulphur proteins

2005 ◽  
Vol 33 (1) ◽  
pp. 20-21 ◽  
Author(s):  
M. Sundararajan ◽  
J.P. McNamara ◽  
M. Mohr ◽  
I.H. Hillier ◽  
H. Wang
Keyword(s):  
Electron Transfer ◽  
Electronic Structure ◽  
Molecular Orbital ◽  
Parametric Method ◽  
Orbital Method ◽  
Molecular Orbital Method ◽  
Semi Empirical

We describe the use of the semi-empirical molecular orbital method PM3 (parametric method 3) to study the electronic structure of iron–sulphur proteins. We first develop appropriate parameters to describe models of the redox site of rubredoxins, followed by some preliminary calculations of multinuclear iron systems of relevance to hydrogenases.

THE INVESTIGATION OF ELECTRONIC PROPERTIES AND MICROSCOPIC SECOND-ORDER NONLINEAR OPTICAL BEHAVIOR OF 1-SALICYLIDENE-3-THIO-SEMICARBAZONE

2007 ◽  
Vol 16 (01) ◽  
pp. 91-99 ◽  
Author(s):  
ASLI KARAKAS ◽  
HUSEYIN UNVER ◽  
AYHAN ELMALI
Keyword(s):  
Molecular Orbital ◽  
Electronic Transition ◽  
Nonlinear Optical ◽  
Dipole Moments ◽  
Empirical Method ◽  
Second Order ◽  
Nlo Properties ◽  
Calculation Results ◽  
Moller Plesset ◽  
Semi Empirical

To investigate the microscopic second-order nonlinear optical (NLO) behavior of the 1-salicylidene-3-thio-semicarbazone Schiff base compound, the electric dipole moments (μ), linear static polarizabilities (α) and first static hyperpolarizabilites (β) have been calculated using finite field second-order Møller-Plesset perturbation (FF MP2) theory. The ab-initio results on (hyper)polarizabilities show that the investigated molecule might have microscopic NLO properties with non-zero values. To understand the NLO behavior in the context of molecular orbital structure, we have also examined the highest occupied molecular orbital (HOMO), the lowest unoccupied molecular orbital (LUMO) and the HOMO-LUMO gap in the same theoretical framework as the (hyper)polarizability calculations. In addition to the NLO properties, the electronic transition spectra have been computed using a semi-empirical method (ZINDO). ZINDO calculation results show that the electronic transition wavelengths have been estimated to be shorter than 400 nm.

Sign in / Sign up

Export Citation Format

Share Document