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Initio MO Calculations (initio + mo_calculation)

Distribution by Scientific Domains
Chemistry100%

Kinds of Initio MO Calculations

  • ab initio mo calculation
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    Selected Abstracts

    The Conformation of Alkyl Benzyl Alcohols Studied by ab initio MO Calculations , A Comparison with IR and NMR Spectroscopic Data

    EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 11 2004
    Osamu Takahashi
    Abstract Ab initio MO calculations were carried out for the conformations of a series of alkyl-substituted benzyl alcohols C6H5CH2CHOH,R (R = CH3, C2H5, iPr, tBu) at the MP2/6-311G(d,p)//MP2/6-31G(d) level. It was found that the conformation where the OH group is gauche to the phenyl group is the most stable. The geometry where both the OH and R groups are close to phenyl is the second most stable. This finding has been interpreted on the grounds of the attractive OH/, and CH/, hydrogen bonds and a repulsive van der Waals interaction between vicinal CH groups. NMR nuclear Overhauser effects, spin-coupling data, and IR spectroscopic data are consistent with the conclusion given by the MO calculations. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source]

    Computational study of base-induced skeletal conversion via a spirocyclic intermediate in dibenzodithiocinium derivatives by ab initio MO calculations

    JOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 5 2003
    Keiji Okada
    Abstract Reaction of 6-methyl-12-oxo-5H,7H -dibenzo[b,g][1,5]dithiocinium salt (1-SO) with methanolic KOH afforded a mixture of dibenzothiepin derivatives 2-SO. In order to clarify the intermediates of the rearrangement, ab initio MO calculations with the HF/6,31G* basis set were performed on the reaction intermediates, the transition states and related compounds. The rearrangement was explained in terms of the usual [2,3]-sigmatropic shift via a spirocyclic intermediate, followed by a 1,3-shift of the sulfonyl group. However, a different type of rearrangement was observed in 6-methyl-5H,7H -dibenzo[b,g][1,5]dithiocinium salt (1-S), giving an unexpected dibenzothiepin derivative 3-S along with a small amount of a ring-opening product 8 under the same reaction conditions. The formation of 3-S and 8 was understandable by the assumption of a cationic intermediate resulting from heterolytic cleavage at the benzyl position. Copyright © 2003 John Wiley & Sons, Ltd. [source]

    Study of carvedilol by combined Raman spectroscopy and ab initio MO calculations

    JOURNAL OF RAMAN SPECTROSCOPY, Issue 10 2002
    M. P. M. Marques
    The novel cardioprotective drug carvedilol was studied by both Raman spectroscopy and ab initio molecular orbital methods (using the density functional theory approach). The spectra, acquired both for the solid samples and DMSO solutions as a function of pH, were assigned in view of the calculated wavenumbers and intensities, and also based on the experimental data obtained for individual compounds which comprise the molecule, namely carbazole and 1,2-dimethoxybenzene. The pH dependence of the Raman pattern of carvedilol was studied, and the pKa value of its secondary amine group was determined (pKa = 8.25) through pH titration experiments. This kind of information is of great significance for the understanding of the biochemical role of carvedilol, which is strongly determined by the acid,base behaviour of the molecule. Copyright © 2002 John Wiley & Sons, Ltd. [source]

    Structural characterization of poly(diethylsiloxane) in the crystalline, liquid crystalline and isotropic phases by solid-state 17O NMR spectroscopy and ab initio MO calculations

    MAGNETIC RESONANCE IN CHEMISTRY, Issue 3 2005
    Hideaki Kimura
    Abstract The structure of poly(diethylsiloxane) (PDES) has been characterized using solid-state NMR of 17O. The sample studied had a weight-average molecular weight of 2.45 × 105. The sample was prepared by utilizing the cationic ring-opening polymerization of 17O-enriched hexacyclotrisiloxane. Solid-state NMR of 17O-enriched PDES was measured on the low-temperature ,1 phase, the high-temperature ,2 phase, the two-phase system consisting of the liquid crystal and isotropic liquid phase and the isotropic phase. From these data, the molecular structure and dynamics of PDES in the various phases were characterized via the chemical shifts of 17O, and electric field gradient parameters were determined from NMR and ab initio molecular orbital (MO) calculations. In addition to the solid-state NMR of 1H, 13C and 29Si previously reported on these samples, knowledge of the dynamic behavior of PDES as inferred from the NMR of 17O in the present study was enhanced significantly. Further, the potential of combining the experimental NMR of 17O with ab initio MO calculations to characterize the dynamics of polymers containing oxygen is demonstrated. Copyright © 2004 John Wiley & Sons, Ltd. [source]

    Sterically Crowded peri -Substituted Naphthalene Phosphines and their PV Derivatives

    CHEMISTRY - A EUROPEAN JOURNAL, Issue 25 2010
    Fergus
    Abstract Three sterically crowded peri -substituted naphthalene phosphines, Nap[PPh2][ER] (Nap=naphthalene-1,8-diyl; ER=SEt, SPh, SePh) 1,3, which contain phosphorus and chalcogen functional groups at the peri positions have been prepared. Each phosphine reacts to form a complete series of PV chalcogenides Nap[P(E,)(Ph2)(ER)] (E,=O, S, Se). The novel compounds were fully characterised by using X-ray crystallography and multinuclear NMR spectroscopy, IR spectroscopy and MS. X-ray data for 1, 2, n,O, n,S, n,Se (n=1,3) are compared. Eleven molecular structures have been analysed by naphthalene ring torsions, peri -atom displacement, splay angle magnitude, X,,,E interactions, aromatic ring orientations and quasi-linear arrangements. An increase in the congestion of the peri region following the introduction of heavy chalcogen atoms is accompanied by a general increase in naphthalene distortion. P,,,E distances increase for molecules that contain bulkier atoms at the peri positions and also when larger chalcogen atoms are bound to phosphorus. The chalcogenides adopt similar conformations that contain a quasi-linear E,,,PC fragment, except for 3,O, which displays a twist-axial-twist conformation resulting in the formation of a linear O,,,SeC alignment. Ab initio MO calculations performed on 2,O, 3,O, 3,S and 3,Se reveal Wiberg bond index values of 0.02 to 0.04, which indicates only minor non-bonded interactions; however, calculations on radical cations of 3,O, 3,S and 3,Se reveal increased values (0.14,0.19). [source]

    Electrophilic Attack on Sulfur,Sulfur Bonds: Coordination of Lithium Cations to Sulfur-Rich Molecules Studied by Ab Initio MO Methods

    CHEMISTRY - A EUROPEAN JOURNAL, Issue 4 2005
    Yana Steudel Dr.
    Abstract Complex formation between gaseous Li+ ions and sulfur-containing neutral ligands, such as H2S, Me2Sn (n = 1,5; Me = CH3) and various isomers of hexasulfur (S6), has been studied by ab initio MO calculations at the G3X(MP2) level of theory. Generally, the formation of LiSn heterocycles and clusters is preferred in these reactions. The binding energies of the cation in the 29 complexes investigated range from ,88 kJ,mol,1 for [H2SLi]+ to ,189 kJ,mol,1 for the most stable isomer of [Me2S5Li]+ which contains three-coordinate Li+. Of the various S6 ligands (chair, boat, prism, branched ring, and triplet chain structures), two isomeric complexes containing the S5S ligand have the highest binding energies (,163±1 kJ,mol,1). However, the global minimum structure of [LiS6]+ is of C3v symmetry with the six-membered S6 homocycle in the well-known chair conformation and three LiS bonds with a length of 256 pm (binding energy: ,134 kJ,mol,1). Relatively unstable isomers of S6 are stabilized by complex formation with Li+. The interaction between the cation and the S6 ligands is mainly attributed to ion,dipole attraction with a little charge transfer, except in cations containing the six sulfur atoms in the form of separated neutral S2, S3, or S4 units, as in [Li(S3)2]+ and [Li(S2)(S4)]+. In the two most stable isomers of the [LiS6]+ complexes, the number of SS bonds is at maximum and the coordination number of Li+ is either 3 or 4. A topological analysis of all investigated complexes revealed that the LiS bonds of lengths below 280 pm are characterized by a maximum electron-density path and closed-shell interaction. [source]