Theoretical studies of azulene and its derivatives

2000 ◽  
Vol 78 (2) ◽  
pp. 224-232 ◽  
Author(s):  
Bo-Cheng Wang ◽  
Yun-Shan Lin ◽  
Jian-Chuang Chang ◽  
Pei-Yu Wang
Keyword(s):  
Ab Initio Calculations ◽  
Ab Initio ◽  
Relative Stability ◽  
Basis Set ◽  
Basis Sets ◽  
Ground State Structure ◽  
Geometrical Isomers ◽  
Bromination Product ◽  
Geometry Analysis ◽  
Dft And Mp2 Calculations

The results of ab initio calculations with the 6-31G basis sets on azulene and its derivatives (including azulenequinones and diazoazulenequinones) are presented in accordance with considerations of their structures and bonding. Azulene is a non-alternant compound with ten π electrons and has either a Cs or C2v symmetry depending on the different carbon bonding. The semiempirical and HF ab initio calculations converge to a Cs symmetry and the DFT and MP2 calculations converge to a C2v symmetry as a ground state structure of azulene. The CIS calculations describe the excited state of azulene and the first excitation energy (S0 - S1) is 533 nm (CIS/6-31+G*), which could illustrate the azure color of azulene. According to the geometry analysis, there are 16 geometrical isomers in azulenequinone conjugated diketones of azulene. Ab initio calculation with the 6-31G basis set generates 1,5- and 1,7-azulenequinone being the most stable isomers of azulenequinone. Theoretically, the relative stability of the bromination product of azulenequinones indicates that 7-bromo-1,5-azulenequinone and 3-bromo-1,7- azulenequinone (for monobromoazulenequinones) and 3,7-dibromo-1,5- azulenequinone and 3,5-dibromo-1,7-azulenequinone (for dibromoazulenequinones) are more stable isomers. The product of diazotization of amino- bromoazulenes is diazoazulenequinone in which a diazo group replaces a ketone group. Isomeric 1,8- and 1,2-diazoazulenequinones are the most stable isomers of diazoazulenequinone according to the theoretical consideration. Due to the resonance and relative stability, diazoazulenequinone may easily extrude nitrogen and form the corresponding triplet ketocarbene intermediate and electronic isomers that undergo photoreaction with THF leading to a polyether bridged azulene (crown type ether). The cyclic reactions in diazoazulenequinone are also studied.Key words: azulene, azulenequinone, diazoazulenequinone, ab initio.

Ab initio studies of isocyanatoborane and difluoroisocyanatoborane; bent or linear BNCO chains?

1991 ◽  
Vol 69 (6) ◽  
pp. 1000-1005 ◽  
Author(s):  
Susan Ellis ◽  
Edward G. Livingstone ◽  
Nicholas P. C. Westwood
Keyword(s):  
Carbon Atom ◽  
Ab Initio Calculations ◽  
Ab Initio ◽  
Potential Surface ◽  
Energy Difference ◽  
Basis Set ◽  
Basis Sets ◽  
Hartree Fock ◽  
Split Valence ◽  
Valence Basis Set

Ab initio calculating at the 3-21G, 6-31G*, 6-31G**, 6-311G*, and 6-311G** Hartree–Fock levels, have been performed on the unknown H2BNCO and F2BNCO molecules in order to establish the geometries of these isoelectronic propadienone analogues. For H2BNCO the double split valence basis sets lead to linear BNCO chains, whereas either a triple split valence basis set, or the inclusion of correlation to second order (MP2/6-31G*) gives trans-bent structures. These have angles at nitrogen of 153.6° (6-311G*) or 149.9° (MP2/6-31G*), with the potential surface for angle bending extremely flat, and 0.5 kJ mol−1 (6-311 G*) or 1.12 kJ mol−1 (MP2/6-31 G*) separating the C2v and Cs structures. For the bent structures there is a small trans-bend (4–6°) at the carbon atom. The F2BNCO molecule is also linear at the 3-21G level, but is, however, already trans-bent (145.6° at nitrogen, 175.9° at carbon) at the 6-31G* Hartree–Fock level; 1.47 kJ mol−1 separates the bent and linear structures. The triple split valence basis set 6-311G* leads to a further decrease in the angle at nitrogen (141.0°), and a similar NCO angle (175.9°), with the bent structure favoured by 3.85 kJ mol−1. MP2/6-31G* calculations give a minimum with an angle at nitrogen of 140.2°, and a bent-linear energy difference of 3.58 kJ mol−1. Key words: ab initio calculations, isocyanatoboranes, structures, quasilinearity, propadienone analogues.

Determination of the Absolute Configuration of Bis(tetrahydropyran2-yl)methane by Comparison of Measured and Calculated CD-spectra

1998 ◽  
Vol 53 (8) ◽  
pp. 704-710 ◽  
Author(s):  
Jörg Fleischhauer ◽  
Christoph Jansen ◽  
Axel Koslowski ◽  
Gerhard Raabe ◽  
Jan Schiffer ◽  
...  
Keyword(s):  
Force Field ◽  
Ab Initio Calculations ◽  
Ab Initio ◽  
Absolute Configuration ◽  
Vibrational Energy ◽  
Basis Set ◽  
Basis Sets ◽  
Am1 Method ◽  
Cd Spectra ◽  
The Absolute

Abstract The absolute configuration of bis(tetrahydropyran-2-yl)methane (1) was determined by comparison of measured and calculated CD spectra. The theoretical CD spectra were obtained by means of the CNDO/2S method. The five presumably lowest local minima on the energy hypersurface of the title compound were used to describe the conformer equilibrium mixture. The geometries of these conformers were calculated employing the MM3 force field, the semiempirical AM1 method and one-determinant ab initio calculations employing the 6-31G* basis set. Boltzmann factors were then obtained using relative energies calculated with three different basis sets and including correlation- and zero point vibrational energy. Based on the sign of the observed and calculated longest wavelength Cotton effect we assign an absolute configuration to the compound which is in keeping with the chirality expected from the assumed reaction mechanism. The results of force field and ab initio calculations converge to the point that the conformer equilibrium is dominated (85 -96%) by one single conformer which is energetically separated from the other conformers by about 2-3 kcal/mol. This result agrees with previous experimental data.

Structures and Stabilities of Small Silicon Cluster: High-Level Ab initio Calculations of Si6

2005 ◽  
Vol 1 (4) ◽  
pp. 343-347 ◽  
Author(s):  
Yi Gao ◽  
Chad Killblane ◽  
X.C. Zeng
Keyword(s):  
Ab Initio Calculations ◽  
Ab Initio ◽  
Experimental Measurement ◽  
Relative Stability ◽  
Basis Sets ◽  
Energy Structure ◽  
Silicon Cluster ◽  
Octahedral Structure ◽  
High Level

The lowest-energy structure of Si6 has been controversial. In this paper, we studied relative stability of this cluster by using the B3LYP, PBE1PBE, MP2, MP4, CCSD, CCSD(T), and QCISD(T) calculations with large basis sets (cc-pVTZ and cc-pVQZ). Our results indicate that the octahedral structure (D4h) is the lowest-energy structure among three isomer candidates studied previously. Our results are also supported by a previous experimental measurement.

A Systematic DFT Study of Two Elementary Steps Involving Hydrogen Peroxide and the Hydroxyl Radical in the Fenton Reaction

2018 ◽  
Author(s):  
Danilo Carmona ◽  
David Contreras ◽  
Oscar A. Douglas-Gallardo ◽  
Stefan Vogt-Geisse ◽  
Pablo Jaque ◽  
...  
Keyword(s):  
Hydrogen Peroxide ◽  
Hydroxyl Radical ◽  
Ab Initio ◽  
Fenton Reaction ◽  
Basis Set ◽  
Basis Sets ◽  
Dft Methods ◽  
Elementary Steps ◽  
Oxygen Oxygen ◽  
Complete Basis Set

The Fenton reaction plays a central role in many chemical and biological processes and has various applications as e.g. water remediation. The reaction consists of the iron-catalyzed homolytic cleavage of the oxygen-oxygen bond in the hydrogen peroxide molecule and the reduction of the hydroxyl radical. Here, we study these two elementary steps with high-level ab-initio calculations at the complete basis set limit and address the performance of different DFT methods following a specific classification based on the Jacob´s ladder in combination with various Pople's basis sets. Ab-initio calculations at the complete basis set limit are in agreement to experimental reference data and identified a significant contribution of the electron correlation energy to the bond dissociation energy (BDE) of the oxygen-oxygen bond in hydrogen peroxide and the electron affinity (EA) of the hydroxyl radical. The studied DFT methods were able to reproduce the ab-initio reference values, although no functional was particularly better for both reactions. The inclusion of HF exchange in the DFT functionals lead in most cases to larger deviations, which might be related to the poor description of the two reactions by the HF method. Considering the computational cost, DFT methods provide better BDE and EA values than HF and post--HF methods with an almost MP2 or CCSD level of accuracy. However, no systematic general prediction of the error based on the employed functional could be established and no systematic improvement with increasing the size in the Pople's basis set was found, although for BDE values certain systematic basis set dependence was observed. Moreover, the quality of the hydrogen peroxide, hydroxyl radical and hydroxyl anion structures obtained from these functionals was compared to experimental reference data. In general, bond lengths were well reproduced and the error in the angles were between one and two degrees with some systematic trend with the basis sets. From our results we conclude that DFT methods present a computationally less expensive alternative to describe the two elementary steps of the Fenton reaction. However, choice of approximated functionals and basis sets must be carefully done and the provided benchmark allows a systematic validation of the electronic structure method to be employed

Vicinal proton—proton coupling constants. Basis set dependence in SCF ab initio calculations

1993 ◽  
Vol 206 (1-4) ◽  
pp. 253-259 ◽  
Author(s):  
Jesús San-Fabián ◽  
Joaquín Guilleme ◽  
Ernesto Díez ◽  
Paolo Lazzeretti ◽  
Massimo Malagoli ◽  
...  
Keyword(s):  
Ab Initio Calculations ◽  
Ab Initio ◽  
Coupling Constants ◽  
Basis Set ◽  
Proton Proton ◽  
Proton Coupling ◽  
Vicinal Proton

scholarly journals Stable Occupancy of Hydrogen Molecules in Clathrate Hydrates and + THF Clathrate Hydrates Determined by Ab Initio Calculations

2010 ◽  
Vol 2010 ◽  
pp. 1-6 ◽  
Author(s):  
Prasad Yedlapalli ◽  
Sangyong Lee ◽  
Jae W. Lee
Keyword(s):  
Ab Initio ◽  
Binding Energies ◽  
Clathrate Hydrates ◽  
Basis Set ◽  
Large Cavity ◽  
Basis Sets ◽  
Pure Hydrogen ◽  
Point Energy ◽  
Small Cavity ◽  
Hydrogen Molecules

Structure II clathrate hydrates of pure hydrogen and binary hydrates of are studied using ab initio calculations to determine the stable occupancies of small cavities. Ab initio calculations are carried out for a double cavity consisting of one dodecahedron (small cavity) and one hexakaidecahedron (large cavity). These two cavities are attached to each other as in sII hydrates to form a double cavity. One or two molecules are placed in the small cavity and one THF (or 4 molecules) molecule is placed in the large cavity. We have determined the binding energies of the double cavities at the MP2 level using various basis sets (3-21G, 3-21G(2p), 3-21 G(2p), 6-31G, 6-31G(2p), and 6-31 G(2p)). Different basis sets yield different stable occupancies of the small cavity. The results from the highest basis set (6-31 G(2p) with zero point energy corrections) indicate that the single occupancy is slightly more favorable than the double occupancy in both the cases of pure hydrates and THF + double hydrates.

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