ChemInform Abstract: MOLECULAR ORBITALS FROM GROUP ORBITALS. 3. QUANTITATIVE PERTURBATIONAL MOLECULAR ORBITAL ANALYSIS OF AB INITIO SCF-MO WAVE FUNCTIONS

1977 ◽  
Vol 8 (21) ◽  
pp. no-no
Author(s):  
M.-H. WHANGBO ◽  
H. B. SCHLEGEL ◽  
S. WOLFE
Keyword(s):  
Ab Initio ◽  
Molecular Orbital ◽  
Molecular Orbitals ◽  
Wave Functions ◽  
Group Orbitals ◽  
Molecular Orbital Analysis ◽  
Orbital Analysis

Molecular orbitals from group orbitals. IV. Quantitative perturbational molecular orbital analysis of the methyl rotational barriers in (CH3)2X molecules. Effect of the fragmentation mode upon the results of the analysis

1977 ◽  
Vol 55 (15) ◽  
pp. 2778-2787 ◽  
Author(s):  
Myung-Hwan Whangbo ◽  
Saul Wolfe
Keyword(s):  
Molecular Orbital ◽  
Qualitative Description ◽  
Orbital Energy ◽  
Orbital Interactions ◽  
Group Orbitals ◽  
Principal Property ◽  
Quantitative Results ◽  
Molecular Orbital Analysis ◽  
Orbital Analysis ◽  
Qualitative Discussion

A quantitative perturbational molecular orbital (PMO) analysis has been performed on ab initio SCF-MO wavefunctions associated with the rotation of the methyl groups in a series of (CH3)2X molecules (X = CH2, O, S, C=O, C=CH2). Two fragmentation modes have been investigated: Method a, in which the system is dissected into X and (CH3)2; and Method b, in which the system is dissected into CH3X and CH3. Both fragmentation modes reproduce the principal property of these molecules, viz., that the more crowded SS conformation is preferred. However, whether this conformational preference is controlled by two-electron stabilizing effects or four-electron destabilizing effects is found to depend upon both the mode of fragmentation and the nature of the substituent X. The quantitative results are supplemented by a detailed qualitative description of the nature of the group orbitals associated with the two fragmentation modes and the various types of orbital interactions. It is shown that orbital energy differences control the qualitative discussion of Method a, and overlap effects control that of Method b. Although the final result, i.e., the preference for the SS conformation, and the behaviour of individual orbital interactions are anticipated correctly by the qualitative arguments, these are unable to assess the relative contributions of the stabilizing and destabilizing interactions.

Ab initio molecular orbital analysis of acetaldehyde dimers.

1998 ◽  
Vol 290 (4-6) ◽  
pp. 431-436 ◽  
Author(s):  
Jose M Hermida-Ramón ◽  
Miguel A Rı́os
Keyword(s):  
Ab Initio ◽  
Molecular Orbital ◽  
Molecular Orbital Analysis ◽  
Orbital Analysis

X-ray molecular orbital analysis. I. Quantum mechanical and crystallographic framework

2018 ◽  
Vol 74 (4) ◽  
pp. 345-356 ◽  
Author(s):  
Kiyoaki Tanaka
Keyword(s):  
Least Squares ◽  
Molecular Orbital ◽  
Molecular Orbitals ◽  
Basis Functions ◽  
X Ray Diffraction ◽  
Covalent Bonds ◽  
X Ray ◽  
Structure Factors ◽  
Molecular Orbital Analysis ◽  
Orbital Analysis

Molecular orbitals were obtained by X-ray molecular orbital analysis (XMO). The initial molecular orbitals (MOs) of the refinement were calculated by the ab initio self-consistent field (SCF) MO method. Well tempered basis functions were selected since they do not produce cusps at the atomic positions on the residual density maps. X-ray structure factors calculated from the MOs were fitted to observed structure factors by the least-squares method, keeping the orthonormal relationship between MOs. However, the MO coefficients correlate severely with each other, since basis functions are composed of similar Gaussian-type orbitals. Therefore, a method of selecting variables which do not correlate severely with each other in the least-squares refinement was devised. MOs were refined together with the other crystallographic parameters, although the refinement with the atomic positional parameters requires a lot of calculation time. The XMO method was applied to diformohydrazide, (NHCHO)2, without using polarization functions, and the electron-density distributions, including the maxima on the covalent bonds, were represented well. Therefore, from the viewpoint of X-ray diffraction, it is concluded that the MOs averaged by thermal vibrations of the atoms were obtained successfully by XMO analysis. The method of XMO analysis, combined with X-ray atomic orbital (AO) analysis, in principle enables one to obtain MOs or AOs without phase factors from X-ray diffraction experiments on most compounds from organic to rare earth compounds.

Effect of the intramolecular hydrogen bond in the active metabolite analogs of leflunomide for blocking the Plasmodium falciparum dihydroorotate dehydrogenase enzyme: QTAIM, NBO, and docking study

2020 ◽  
Vol 16 ◽  
Author(s):  
Reihaneh Heidarian ◽  
Mansoureh Zahedi-Tabrizi
Keyword(s):  
Hydrogen Bond ◽  
Plasmodium Falciparum ◽  
Molecular Orbital ◽  
Intramolecular Hydrogen Bond ◽  
Active Metabolite ◽  
Chemical Hardness ◽  
Dihydroorotate Dehydrogenase ◽  
Molecular Orbital Analysis ◽  
Intramolecular Hydrogen ◽  
Orbital Analysis

: Leflunomide (LFM) and its active metabolite, teriflunomide (TFM), have drawn a lot of attention for their anticancer activities, treatment of rheumatoid arthritis and malaria due to their capability to inhibit dihydroorotate dehydrogenase (DHODH) and Plasmodium falciparum dihydroorotate dehydrogenase (PfDHODH) enzyme. In this investigation, the strength of intramolecular hydrogen bond (IHB) in five analogs of TFM (ATFM) has been analyzed employing density functional theory (DFT) using B3LYP/6-311++G (d, p) level and molecular orbital analysis in the gas phase and water solution. A detailed electronic structure study has been performed using the quantum theory of atoms in molecules (QTAIM) and the hydrogen bond energies (EHB) of stable conformer obtained in the range of 76-97 kJ/mol, as a medium hydrogen bond. The effect of substitution on the IHB nature has been studied by natural bond orbital analysis (NBO). 1H NMR calculations show an upward trend in the proton chemical shift of the enolic proton in the chelated ring (14.5 to 15.7ppm) by increasing the IHB strength. All the calculations confirmed the strongest IHB in 5-F-ATFM and the weakest IHB in 2-F-ATFM. Molecular orbital analysis, including the HOMO-LUMO gap and chemical hardness, was performed to compare the reactivity of inhibitors. Finally, molecular docking analysis was carried out to identify the potency of inhibition of these compounds against PfDHODH enzyme.

UPS Study of [2,2] (2,5)Furanophane and [2,2] (2,5)Thiophenophane Evidence Regarding the Importance of Through Bond and Through Space Interactions

1978 ◽  
Vol 33 (8) ◽  
pp. 959-963 ◽  
Author(s):  
Fernando Bernardi ◽  
Andrea Bottoni ◽  
Francesco Paolo Colonna ◽  
Giuseppe Distefano ◽  
Ugo Folli ◽  
...  
Keyword(s):  
Molecular Orbital ◽  
Photoelectron Spectra ◽  
Molecular Orbital Analysis ◽  
Orbital Analysis

The ultraviolet photoelectron spectra of [2,2](2,5)furanophane (FUPH) and [2,2](2,5)thiophenophane (THPH) have been analyzed on the basis of a perturbational molecular orbital analysis, by comparison with CNDO/2 computations and by correlating them with the spectra of related molecules. Through space and through bond interactions between the two heteroaromatic rings are shown to be important in determining the ordering of the outermost MO’s in this class of compounds.

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