scholarly journals Ab Initioand DFT Studies of Conformational Properties of Heteroatom Containing Ketene Analogues and Their Comparison with the Related Cyclic Analogues

2012 ◽  
Vol 9 (1) ◽  
pp. 193-202 ◽  
Author(s):  
S. Zahra Sayyed-Alangi ◽  
Mohammad T. Baei
Keyword(s):  
Transition State ◽  
Minimum Energy ◽  
Basis Set ◽  
Global Minima ◽  
Stable Conformer ◽  
Trans Conformation ◽  
Conformational Interconversion ◽  
Conformational Properties ◽  
Torsional Angles ◽  
Single Bonds

Minimum-energy and transition state geometries of 3-thioxoprop-2-enethial, 3-thioxoacrylaldehyde, 3-oxoprop-2-enethial, 3-selenoxoprop-2-enethial, 3-thioxoprop-2-eneselenal, 3-selenoxoprop-2-eneselenal, 3-oxoacrylaldehyde, 3-selenoxoacrylaldehyde and 3-oxoprop-2-eneselenal were calculated using HF, B3LYP and MP2 levels of theory and 6-31+G*basis set by rotation around the related -C-C- single bonds. In all of the above mentioned molecules, the s-trans conformation was obtained as the most stable conformer with the 180°dihedral angle, apart from 3-oxoprop-2-enethial and 3-thioxoprop-2-eneselenal which theirs-cisconformers were appeared more stability than related tos-transforms. Their perpendicular geometries, with torsional angles approximately 90°, were as transition state for conformational interconversion between the two global minima forms. Cyclic structures all of the above mentioned molecules were unstable than their linear forms.

Abinitio study of rotational isomerism in acrolein

1985 ◽  
Vol 63 (7) ◽  
pp. 1672-1680 ◽  
Author(s):  
George R. De Maré
Keyword(s):  
Potential Energy ◽  
Transition State ◽  
Dipole Moments ◽  
Relative Energy ◽  
Rotational Isomerism ◽  
Basis Set ◽  
Gradient Force ◽  
Trans Conformation ◽  
Torsional Potential ◽  
Trans Conformer

Analytic gradient (force) methods at the STO-3G, 3-21G, and 6-31G* basis set levels have been used to optimize the geometry of acrolein completely at each critical point (minima, maximum) in the torsional potential energy curves for rotation about the single C—C bond (dihedral angle θ). The STO-3G and 6-31G* optimizations predict the planar trans conformation (θ = 180°) to be more stable than the cis conformation (θ = 0°) by 1.87 and 6.97 kJ/mol, respectively. The 3-21G optimizations, in disagreement with experiment, place the planar cis structure below the trans by 4.5 J/mol. The predicted relative energy (ΔE) and position for the transition state (TS) for rotation from the trans conformer are ΔE = 22.35, 37.14, and 34.41 kJ/mol and θ = 91.8, 91.6, and 91.0° for the STO-3G, 3-21G, and 6-31G* optimizations, respectively. The computed and experimental geometries, relative energies, dipole moments, and coefficients for the torsional potential expansion are compared.

Computational study on the reaction of atomic chlorine with 1,2-dibromoethane (CH2BrCH2Br)

2013 ◽  
Vol 91 (11) ◽  
pp. 1123-1129 ◽  
Author(s):  
Ang-yang Yu
Keyword(s):  
Transition State ◽  
Rate Constants ◽  
Transition State Theory ◽  
Computational Study ◽  
Minimum Energy ◽  
State Theory ◽  
Basis Set ◽  
Stationary Points ◽  
Variational Transition State Theory ◽  
Variational Transition State

In this work, the reaction mechanism and kinetics of Cl + CH2BrCH2Br → products are theoretically investigated for the first time. The optimized geometries and frequencies of all of the stationary points and selected points along the minimum-energy path for the three hydrogen abstraction channels and two bromine abstraction channels are calculated at the BH&H-LYP level with the 6-311G** basis set and the energy profiles are further calculated at the CCSD(T) level of theory. The rate constants are evaluated using the conventional transition-state theory, the canonical variational transition-state theory, and the canonical variational transition-state theory with a small-curvature tunneling correction over the temperature range 200–1000 K. The results show that reaction channel 3 is the primary channel and the calculated rate constants are in good agreement with available experimental values. The three-parameter Arrhenius expression for the total rate constants over 200–1000 K is provided.

A study of the conformational profile and the vibrational spectra of the plant hormone indole-3-acetic acid

2014 ◽  
Vol 13 (01) ◽  
pp. 1350073 ◽  
Author(s):  
Wolfgang Förner ◽  
Hassan M. Badawi
Keyword(s):  
Acetic Acid ◽  
Basis Set ◽  
Normal Coordinate ◽  
Stable Conformer ◽  
Vibrational Assignments ◽  
B3lyp Calculations ◽  
Normal Mode Calculations ◽  
Full Optimization ◽  
Torsional Angles ◽  
Indole 3 Acetic Acid

The structural stability of indole-3-acetic acid was investigated by DFT-B3LYP calculations with the 6-311G** basis set. From the calculations the gauche–gauche (gg) structure was predicted to be the second lowest energy minimum for the acid. It is energetically only 0.57 kcal/mol above the lowest conformer which is the trans–cis (tc) structure. A further stable conformer, however, highest in energy, is the trans–trans (tt) one, which is by 2.68 kcal/mol higher in energy than tc. The tc conformer upon full optimization turned a little bit away from real tc to a near tc (ntc) structure (defining torsional angles only changed by a few decigrades). However, the X-ray data indicate a structure in the solid, which is most similar to gg, stabilized by intermolecular eight ring hydrogen bonds. In the present DFT calculations such stabilizations cannot be accounted for, because the calculations treat only isolated molecules. To take such interactions into account at least dimers would have to be optimized. Therefore the vibrational frequencies of the gg conformer were computed at the B3LYP level of theory and tentative vibrational assignments were provided on the basis of normal coordinate analysis, normal mode calculations and experimental infrared and Raman data. However, some of the observed lines are obviously due to a small amount of the tc conformer present.

Conformational Preferences of ortho-Substituted Benzophenones. Correlations Between Carbon-13 Nuclear Magnetic Resonance Shieldings and Calculated Torsional Angles

1973 ◽  
Vol 51 (7) ◽  
pp. 1053-1059 ◽  
Author(s):  
Gerald Wallace Buchanan ◽  
Giorgio Montaudo ◽  
Paulo Finocchiaro
Keyword(s):  
Minimum Energy ◽  
Conformational Energy ◽  
Conformational Preference ◽  
Contour Maps ◽  
Linear Relationships ◽  
Conformational Energy Calculations ◽  
Conformational Preferences ◽  
Conformational Properties ◽  
Torsional Angles ◽  
Semi Empirical

The results of an investigation of the conformational properties of some benzophenones are reported. Carbon-13 n.m.r. spectra provide a generally applicable method to study the conformational preference of these compounds through the C=O shifts. Semi-empirical conformational energy calculations have been used to build contour maps of relative conformational energy as a function of the two internal rotation angles of these molecules. Conformations of minimum energy, as detected from the contour maps, have been assumed as the most stable. The phenyl torsional angles corresponding to these conformations, plotted against the C=O shifts, furnish linear relationships.

Comparison of the Conformational Stability for Several Vinylhalomethanes and Silanes with Experiment Using MP2 Perturbation Theory and DFT

2007 ◽  
Vol 72 (1) ◽  
pp. 15-50 ◽  
Author(s):  
Wolfgang Förner ◽  
Hassan M. Badawi
Keyword(s):  
Experimental Data ◽  
Vibrational Spectra ◽  
Recent Literature ◽  
Conformational Stability ◽  
Basis Set ◽  
Major Conclusion ◽  
Stable Conformer ◽  
Polarization Functions ◽  
Complete Series ◽  
Triple Zeta

In recent literature it was reported that the valence triple zeta basis set augmented by polarization functions is not too reliable for vinyl monohalo- and dihalomethanes and -silanes, the halogen being fluorine and chlorine. The major conclusion was that a valence triple zeta basis is too small to be augmented by polarization functions in a balanced way, at least on vinylmonofluoromethane. Thus we decided to apply the 6-311++G** basis set to the complete series of methanes, silanes and germanes (the latter ones are just added for completeness because no experimental data are available for them and, moreover, we published them already previously) and to compare the results to experimental data available in the literature to see whether the failures of this basis set show up in the complete series of molecules. In the literature we found five such molecules and the information which of the conformers is the most stable. Indeed we found that predictions on the relative stability of conformers in those systems with this basis set and MP2 as well as DFT are with a 60:40 chance, three being correct predictions and two being incorrect ones out of the five. However, since the energy differences are rather small in these systems and due to the fact that - as a consequence of twofold degeneracy of the gauche conformer on the potential curve of the torsional vibration - the abundances of the conformers in equilibrium do not change too much, we decided to calculate also vibrational spectra for three examples and to compare them also to experiment. It is reported that besides the failures in total energy (we have chosen two examples where predictions of the nature of the stable conformer are correct, and one where it is not), the vibrational spectra are rather well reproduced, especially when experimental energies are used to calculate abundances in equilibrium in the case where the prediction of the stable conformer failed.

Allowed and Forbidden Reaction Paths for the H2 + D2 Exchange Reaction

1975 ◽  
Vol 53 (4) ◽  
pp. 549-555 ◽  
Author(s):  
James S. Wright
Keyword(s):  
Transition Metal ◽  
Transition State ◽  
Exchange Reaction ◽  
Barrier Height ◽  
Dissociation Energy ◽  
Basis Set ◽  
Reaction Paths ◽  
Double Zeta ◽  
Double Zeta Basis

Symmetry arguments and abinitio s.c.f. calculations (double-zeta basis set) are used to show that the exchange reaction H2+ D2 → 2HD could proceed in a concerted fashion through a six-center transition state. The computed barrier height of 90 kcal/mol for this process lies below the experimental dissociation energy of H2 (but above the computed dissociation energy) and also below the energy required for exchange through a four-center transition state. Either the termolecular(2 + 2 + 2 ) or bimolecular(4 + 2 ) cycloadditions are thermally allowed. The presence of a transition metal would allow the reaction to proceed through a four-center geometry, leading to the formation of a possibly stable metal-H4 complex.

scholarly journals Density functional theory (DFT) calculations of conformational energies and interconversion pathways in 1,2,7-thiadiazepane

2011 ◽  
Vol 76 (3) ◽  
pp. 395-406 ◽  
Author(s):  
Mina Haghdadi ◽  
Nahid Farokhi
Keyword(s):  
Density Functional Theory ◽  
Dft Calculations ◽  
Density Functional ◽  
Activation Barrier ◽  
Stable Conformer ◽  
Functional Theory ◽  
Conformational Interconversion ◽  
Interconversion Barrier ◽  
The One ◽  
Twist Boat

The molecular structure and conformational analysis of 1,2,7-thiadiazapane conformers were investigated by density functional theory (DFT) calculations at the B3LYP/cc-pVDZ level of theory. Four twist-chair (TC), six twist-boat (TB), two boat (B), two chair (C) and four twist (T) conformers were identified as minima and transition states for 1,2,7-thiadiazepane. The TC1 conformer is the most stable conformer and the twist-chair conformers are predicted to be lower in energy than their corresponding boat and chair conformations. DFT predicts a small barrier to pseudo-rotation and a remarkable activation barrier for the conformational interconversion of the twist-chair conformers to their corresponding boat conformers. The simplest conformational process and the one with the lowest barrier is the degenerate interconversion of the twist-chair 3 (TC3) conformation with itself via the CS symmetric chair (C2) transition state. The calculated strain energy barrier for this process is 2.41 kJ mol-1. The highest conformational interconversion barrier is between TC2 and twistboat 3 (TB3) forms, which was found to be 75.62 kJ mol-1.

Potential Energy Surface Calculations of Alanine Dipeptide using BVWN Density Functional Approach and 6-311G Basis Set

2009 ◽  
Vol 1219 ◽  
Author(s):  
Jyoti Singh ◽  
Subhash Chandra Singh ◽  
Narsingh Bahadur Singh
Keyword(s):  
Potential Energy ◽  
Potential Energy Surfaces ◽  
Density Functional ◽  
Basis Set ◽  
Reaction Coordinates ◽  
Conformational Properties ◽  
Energy Surfaces ◽  
Polypeptide Chains ◽  
Alanine Dipeptide

AbstractThis work is devoted to a study of the conformational properties of alanine dipeptide. We have studied potential energy surfaces of alanine dipeptide molecule using density functional theoretical approach with 6-311G basis set. For this purpose potential energies of this molecule are calculated as a function of Ramachandran angles φ and ψ, which are important factors for the characterizations of polypeptide chains. These degrees of freedoms φ and ψ are important for the characterization of protein folding systems. Stable conformations, energy barriers and reaction coordinates of this important dipeptide molecule are calculated. Energy required for the transition of one conformation into other are also discussed.

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