The ozonolysis of ortho-xylene and its relevance to the history of the benzene problem

2001 ◽  
Vol 79 (8) ◽  
pp. 1278-1283 ◽  
Author(s):  
Saul Wolfe ◽  
Zheng Shi
Keyword(s):  
Density Functional Theory ◽  
Density Functional ◽  
Transition States ◽  
Historical Analysis ◽  
Valence Bond ◽  
Basis Set ◽  
Frontier Molecular Orbital ◽  
Initial Attack ◽  
Orbital Theory ◽  
Functional Theory

Using B3LYP density functional theory in conjunction with the 6-311++G** basis set, the relative rates of the initial rate-determining attack of ozone upon the carbon—carbon bonds of o-xylene are found to be 4,5- [Formula: see text] 3,4- > 2,3- > 1,2-. With the assumption that the final products glyoxal (G), methylglyoxal (M), and dimethylglyoxal (D) are determined by the site of the initial attack, and taking statistical factors into account, the ratio G:M:D is calculated to be 3:2:1. This is close to the value found experimentally, and identical to the result predicted by the contention that two nearly equivalent Kekulé–Pauling valence bond (resonance) structures of o-xylene exist and each localized carbon—carbon double bond of these structures is oxidized at the same rate. Although Frontier Molecular Orbital theory also predicts a 3:2:1 ratio of G:M:D, this theory incorrectly predicts that the initial attack of ozone will take place at the 1,2- and 4,5- bonds, with 1,2-attack slightly preferred. These results are discussed in relation to a recent historical analysis of the benzene problem, and it is concluded that since the products of ozonolysis of o-xylene are determined by the relative energies of the transition states leading to the four possible primary ozonides, these transition states should be the focus of theory.Key words: Kekulé structure, resonance, frontier orbital theory, density functional theory, kinetics.

THE H2NO POTENTIAL ENERGY SURFACE EXPLORED WITH HIGH LEVEL AB INITIO AND DENSITY FUNCTIONAL THEORY METHODS

2007 ◽  
Vol 06 (03) ◽  
pp. 549-562
Author(s):  
ABRAHAM F. JALBOUT
Keyword(s):  
Density Functional Theory ◽  
Potential Energy ◽  
Potential Energy Surface ◽  
Density Functional ◽  
Energy Surface ◽  
Hybrid Methods ◽  
Transition States ◽  
Basis Set ◽  
Functional Theory ◽  
High Level

The transition states for the H 2 NO decomposition and rearrangements mechanisms have been explored by the CBS-Q method or by density functional theory. Six transition states were located on the potential energy surface, which were explored with the Quadratic Complete Basis Set (CBS-Q) and Becke's one-parameter density functional hybrid methods. Interesting deviations between the CBS-Q results and the B1LYP density functional theory lead us to believe that further study into this system is necessary. In the efforts to further assess the stabilities of the transition states, bond order calculations were performed to measure the strength of the bonds in the transition state.

scholarly journals Molecular Structures and Spectral Properties of Natural Indigo and Indirubin: Experimental and DFT Studies

Molecules ◽  
2019 ◽  
Vol 24 (21) ◽  
pp. 3831 ◽  
Author(s):  
Zixin Ju ◽  
Jie Sun ◽  
Yanping Liu
Keyword(s):  
Density Functional Theory ◽  
Spectral Properties ◽  
Density Functional ◽  
Dft Method ◽  
Molecular Structures ◽  
Basis Set ◽  
Frontier Molecular Orbital ◽  
Visible Absorption ◽  
Functional Theory ◽  
Uv Visible

This paper presents a comparative study on natural indigo and indirubin in terms of molecular structures and spectral properties by using both computational and experimental methods. The spectral properties were analyzed with Fourier transform infrared (FTIR), Raman, UV-Visible, and fluorescence techniques. The density functional theory (DFT) method with B3LYP using 6-311G(d,p) basis set was utilized to obtain their optimized geometric structures and calculate the molecular electrostatic potential, frontier molecular orbitals, FTIR, and Raman spectra. The single-excitation configuration interaction (CIS), time-dependent density functional theory (TD-DFT), and polarization continuum model (PCM) were used to optimize the excited state structure and calculate the UV-Visible absorption and fluorescence spectra of the two molecules at B3LYP/6-311G(d,p) level. The results showed that all computational spectra agreed well with the experimental results. It was found that the same vibrational mode presents a lower frequency in indigo than that in indirubin. The frontier molecular orbital analysis demonstrated that the UV-Visible absorption and fluorescence bands of indigo and indirubin are mainly derived from π → π* transition. The results also implied that the indigo molecule is more conjugated and planar than indirubin, thereby exhibiting a longer maximum absorption wavelength and stronger fluorescence peak.

scholarly journals DFT and TD-DFT Study of Only First Diaminomalenonitrile Based Molecular Receptor for Fluoride Anion: Correlation of Calculated and Experimental Results

2021 ◽  
Vol 13 (3) ◽  
pp. 923-933
Author(s):  
M. A. Kaloo ◽  
H. Bashir ◽  
M. A. Rather ◽  
S. A. Majid ◽  
B. A. Bhat
Keyword(s):  
Density Functional Theory ◽  
Density Functional ◽  
Energy Gap ◽  
Atomic Orbital ◽  
Basis Set ◽  
Frontier Molecular Orbital ◽  
Fluoride Anion ◽  
Functional Theory ◽  
Sensing Mechanism ◽  
Td Dft

In this work, the sensing mechanism of a novel anion receptor, 2-amino-((E)-(4-cyanobenzalidine) amino) maleonitrile reported by Sankar et al. (Analyst 138:4760-4763, 2013) was investigated theoretically with the help of density functional theory (DFT) and time-dependent density functional theory (TD-DFT). From the frontier molecular orbital analysis, it is reasonable to support the proposed charge transfer (ICT) enhancement in the receptor molecule in the presence of F−. A significant reduction in the energy gap (ΔE) from 4.014 eV to 2.342eV between highest occupied and lowest unoccupied energy levels was revealed, leading to the strong redshift of its absorption characteristics. Moreover, 1H NMR was also calculated to further understand the mechanistic insights by using the gauge independent atomic orbital (GIAO) method with B3LYP methods and the 6-311++G (d,p) basis set. The spectra were simulated, and the chemical shifts linked to TMS were compared with experimental. Besides, Intrinsic Reaction Coordinates (IRC) were also calculated to understand the sensing mechanism.

Solvent effect on the Molecular structure and Global, Local and Dual Descriptors: A Density Functional Theory Study

2021 ◽  
pp. 305-315
Author(s):  
Faiza Lehraki ◽  
Nadjib Melkemi
Keyword(s):  
Density Functional Theory ◽  
Dipole Moment ◽  
Density Functional ◽  
Basis Set ◽  
Frontier Molecular Orbital ◽  
Nucleophilic Attack ◽  
Functional Theory ◽  
Fukui Functions ◽  
Reactivity Descriptors ◽  
Polarized Continuum Model

This study aims to explore the effects of solvent polarity on the geometry, energy of solvation, dipole moment, polarizability, charge distribution, frontier molecular orbital analysis, and global, local, and dual descriptors for β Carboline. The effects of eight solvents were treated using a conductor-like polarized continuum model. Density Functional Theory calculations were performed at B3LYP level at 6-311++g (d,p) basis set. The computed results showed that the dipole moment, polarizability, the solvation free energy, and atomic charge of β Carboline increased with the increasing polarity of the solvent. Also, the solvation modified the values of the reactivity descriptors as a result of the interaction between the solvent and β Carboline. The dual descriptor provided a clearer difference between electrophilic and nucleophilic attack at specific atomic site than presented by Fukui functions of β Carboline.

scholarly journals X-ray diffraction and Density Functional Theory based structural analyses of 2-phenyl-4-(prop-2-yn-1-yl)-1,2,4-triazolone

2021 ◽  
Vol 12 (4) ◽  
pp. 459-468
Author(s):  
Shilpa Mallappa Somagond ◽  
Ahmedraza Mavazzan ◽  
Suresh Fakkirappa Madar ◽  
Madivalagouda Sannaikar ◽  
Shankar Madan Kumar ◽  
...  
Keyword(s):  
Density Functional Theory ◽  
Density Functional ◽  
Energy Gap ◽  
Basis Set ◽  
Frontier Molecular Orbital ◽  
Geometrical Parameters ◽  
Monoclinic Space Group ◽  
X Ray Diffraction ◽  
Functional Theory ◽  
X Ray

This study is composed of X-ray diffraction and Density Functional Theory (DFT) based molecular structural analyses of 2-phenyl-4-(prop-2-yn-1-yl)-2,4-dihydro-3H-1,2,4-triazol-3-one (2PPT). Crystal data for C11H9N3O: Monoclinic, space group P21/c (no. 14), a = 7.8975(2) Å, b = 11.6546(4) Å, c = 11.0648(3) Å, β = 105.212(2)°, V = 982.74(5) Å3, Z = 4, T = 296.15 K, μ(MoKα) = 0.091 mm-1, Dcalc = 1.346 g/cm3, 13460 reflections measured (5.174° ≤ 2Θ ≤ 64.72°), 3477 unique (Rint = 0.0314, Rsigma = 0.0298) which were used in all calculations. The final R1 was 0.0470 (I > 2σ(I)) and wR2 was 0.1368 (all data). The experimentally determined data was supported by theoretically optimized calculations processed with the help of Hartree-Fock (HF) technique and Density Functional Theory with the 6-311G(d,p) basis set in the ground state. Geometrical parameters (Bond lengths and angles) as well as spectroscopic (FT-IR, 1H NMR, and 13C NMR) properties of 2PPT molecule has been optimized theoretically and compared with the experimentally obtained results. Hirshfeld surface analysis with 2D fingerprinting plots was used to figure out the possible and most significant intermolecular interactions. The electronic characterizations such as molecular electrostatic potential map (MEP) and Frontier molecular orbital (FMO) energies have been studied by DFT/B3LYP approach. The MEP imparted the detailed information regarding electronegative and electropositive regions across the molecule. The HOMO-LUMO energy gap as high as 5.3601 eV was found to be responsible for the high kinetic stability of the 2PPT.

Benchmark of Simplified Time-Dependent Density Functional Theory for UV-Vis Spectral Properties of Porphyrinoids

2019 ◽  
Author(s):  
Kamal Batra ◽  
Stefan Zahn ◽  
Thomas Heine
Keyword(s):  
Density Functional Theory ◽  
Density Functional ◽  
Large Scale ◽  
Absolute Error ◽  
Time Dependent ◽  
Basis Set ◽  
Basis Sets ◽  
Functional Theory ◽  
Framework Materials ◽  
Dependent Density

<p>We thoroughly benchmark time-dependent density- functional theory for the predictive calculation of UV/Vis spectra of porphyrin derivatives. With the aim to provide an approach that is computationally feasible for large-scale applications such as biological systems or molecular framework materials, albeit performing with high accuracy for the Q-bands, we compare the results given by various computational protocols, including basis sets, density-functionals (including gradient corrected local functionals, hybrids, double hybrids and range-separated functionals), and various variants of time-dependent density-functional theory, including the simplified Tamm-Dancoff approximation. An excellent choice for these calculations is the range-separated functional CAM-B3LYP in combination with the simplified Tamm-Dancoff approximation and a basis set of double-ζ quality def2-SVP (mean absolute error [MAE] of ~0.05 eV). This is not surpassed by more expensive approaches, not even by double hybrid functionals, and solely systematic excitation energy scaling slightly improves the results (MAE ~0.04 eV). </p>

scholarly journals Density Functional Theory and Complete Basis Set Ab Initio Computational Study of Five-, Six-, Seven- and Eight-hydrogen Coordinated Carbon Cations

1999 ◽  
Vol 23 (8) ◽  
pp. 502-503
Author(s):  
Branko S. Jursic
Keyword(s):  
Density Functional Theory ◽  
Ab Initio ◽  
Density Functional ◽  
Computational Study ◽  
Basis Set ◽  
Functional Theory ◽  
Complete Basis ◽  
Complete Basis Set ◽  
High Level

High level ab initio and density functional theory studies are performed on highly protonated methane species.

Dissociation of dinitrogen on iron clusters: A detailed study of the Fe16 + N2 case.

2020 ◽  
Author(s):  
Bole Chen ◽  
Gennady L. Gutsev ◽  
Weiguo Sun ◽  
Xiao-Yu Kuang ◽  
Cheng Lu ◽  
...  
Keyword(s):  
Density Functional Theory ◽  
Density Functional ◽  
Basis Set ◽  
Generalized Gradient ◽  
Functional Theory ◽  
Iron Clusters ◽  
Generalized Gradient Approximation

The coalescence of two Fe8N as well as the structure of the Fe16N2 cluster were studied using density functional theory with the generalized gradient approximation and a basis set of...

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