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Electron Cloud (electron + cloud)
Selected AbstractsSynthesis and Characterization of the Very Bulky Phenols Ar*OH and Ar,OH (Ar* = C6H3 -2,6-Trip2, Trip = C6H2 -2,4,6- iPr3; Ar, = C6H3 -2,6-Dipp2, Dipp = C6H3 -2,6- iPr2) and Their Lithium and Sodium Derivatives (LiOAr,)2 and (NaOAr*)2EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 18 2003Corneliu Stanciu Abstract The very bulky phenols Ar*OH (1) and Ar,OH (2), where Ar* = C6H3 -2,6-Trip2 (Trip = C6H2 -2,4,6- iPr3) and Ar, = C6H3 -2,6-Dipp2 (Dipp = C6H3 -2,6- iPr2), as well as their lithium and sodium derivatives (LiOAr*)2 (3), (LiOAr,)2 (4) and (NaOAr*)2 (5) have been synthesized and characterized. The terphenols 1 and 2 were obtained by the reaction of the aryllithium reagents with nitrobenzene and were isolated in ca. 70% yield. The lithium or sodium salts 3,5 were isolated by the reaction of 1 or 2 with nBuLi or sodium metal. All compounds were characterized spectroscopically, and by X-ray crystallography in the case of 1, 2, 4 and 5. The large terphenyl substituents prevent hydrogen-bonded association of the phenols 1 and 2. Instead, the O,H hydrogens interact with the ,-electron cloud on one of the flanking Trip or Dipp rings. The dimeric structures of 4 and 5 are relatively rare examples of structurally characterized alkali metal phenoxides that are unsolvated by internal electron pair donors or classical Lewis bases such as ethers or amines. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) [source] Length-dependence of electron transfer coupling matrix in polyene wires: Ab initio molecular orbital theory study,INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 6 2009Govind Mallick Abstract The electron transfer (ET) properties of ,-electron conjugated quasi-one-dimensional molecular wires, consisting of polyene, [>CC<]n (n = 1,11), including ,-carotene, is investigated using ab initio molecular orbital theory within Koopmans theorem (KT) approach. The ET coupling matrix element, VDA, for 1,3- trans -butadiene molecule calculated with the KT approach shows excellent agreement with the corresponding results obtained with two-state model. The calculated values of VDA for the polyene oligomers exhibit exponential decrease in magnitude with increasing length of the wire. However, the decay curve exhibits three different regimes. The magnitude of the decay constant, ,, decreases with the increase in length of the wire. A highly delocalized ,-electron cloud in the polyene chain appears to facilitate retention of the electronic coupling at large separations between the donor and acceptor centers. Published 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2009 [source] Development of a general quantum-chemical descriptor for steric effects: Density functional theory based QSAR study of herbicidal sulfonylurea analoguesJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 13 2006Zhen Xi Abstract Quantitative structure-activity relationship (QSAR) analysis has become one of the most effective approaches for optimizing lead compounds and designing new drugs. Although large number of quantum-chemical descriptors were defined and applied successfully, it is still a big challenge to develop a general quantum-chemical descriptor describing the bulk effects more directly and effectively. In this article, we defined a general quantum-chemical descriptor by characterizing the volume of electron cloud for specific substituent using the method of density functional theory. The application of our defined steric descriptors in the QSAR analysis of sulfonylurea analogues resulted in four QSAR models with high quality (the best model: q2 = 0.881, r2 = 0.901, n = 35, s = 0.401, F = 68.44), which indicated that this descriptor may provide an effective way for solving the problem how to directly describe steric effect in quantum chemistry-based QSAR studies. © 2006 Wiley Periodicals, Inc. J Comput Chem 27: 1571,1576, 2006 [source] Royal crown-shaped electride Li3 -N3 -Be containing two superatoms: New knowledge on aromaticityJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 8 2006Zhi-Ru Li Abstract The structure and aromaticity of a royal crown-shaped molecule Li3 -N3 -Be are studied at the CCSD(T)/aug-cc-pVDZ level. This molecule is a charge-separated system and can be denoted as Li32+N33,Be+. It is found that the Li32+ ring exhibits aromaticity mainly because the Li32+ ring can share the ,-electron with the N3,3 ring. The 4n+2 electron counter rule can be satisfied for the Li32+ subunit if the shared , valence electron of N33, subunit is also taken into account. This new knowledge on aromaticity of a ring from the interactions between subunits is revealed first time in this paper. Li3 -N3 -Be can be also regarded as a molecule containing two superatoms (Li3 and N3), which may be named as a "superomolecule." Li3 -N3 -Be is a new metal,nonmetal,metal type sandwich complex. The N33, trianion in the middle repulses the electron clouds of the two metal subunits (mainly to the Li3 superatom) to generate an excess electron, and thus Li3 -N3 -Be is also an electride. This phenomenon of the repulsion results in: (a) the HOMO energy level increased, (b) the electron cloud in HOMO distended, (c) the area of the negative NICS value extended, and (d) the VIE value lowered. So the superomolecule Li3 -N3 -Be is not only a new metal,nonmetal,metal type sandwich complex but also a new type electride, which comes from the interaction between the alkali superatom (Li3) and the nonmetal superatom (N3). © 2006 Wiley Periodicals, Inc. J Comput Chem 27: 986,993, 2006 [source] Application of CAMD in separating hydrocarbons by extractive distillationAICHE JOURNAL, Issue 12 2005Biaohua Chen Abstract The solvent is the core of extractive distillation, and a suitable solvent plays an important role in the economical design of extractive distillation. Computer-aided molecular design (CAMD) has been applied to rapidly screen the solvents for separating hydrocarbons by extractive distillation. The systems of propane/propylene, n-butane/1-butene, and n-heptane/benzene, respectively, as the representatives of C3, C4, and C6 hydrocarbons were investigated, and the potential solvents were selected by means of CAMD. The designed results were further proven by experiments and process simulation. The mechanism for separating hydrocarbons by extractive distillation is based on the different fluidities of the electron cloud of CC (no double bond), CC (one double bond), and ACH (aromatic carbon ring) bonds and thus different interactions between solvent and hydrocarbon molecules. To improve the separation ability of the main solvent, one strategy is to add some additive that can form hydrogen bonding with the main solvent to make into a mixture. © 2005 American Institute of Chemical Engineers AIChE J, 2005 [source] C,H..., interactions in cocrystals of bis(trimethylsilyl)acetylene and diphenylacetylene with benzeneACTA CRYSTALLOGRAPHICA SECTION C, Issue 4 2010Frank Meyer-Wegner We present here the crystal structures of two acetylene derivatives cocrystallized with benzene, namely bis(trimethylsilyl)acetylene benzene solvate, C8H18Si2·C6H6, (I), and diphenylacetylene benzene solvate, C14H10·C6H6, (II). In (I), both molecules belong to the symmetry point group C2h and are located about special positions with site symmetry 2/m. In (II), both molecules show crystallographic inversion symmetry. In both structures, there are C,H..., contacts between aromatic H atoms and the ,-electrons of the triple bond. In addition to these, in (II) there are C,H..., contacts between aromatic H atoms and the ,-electron cloud of the benzene molecules. [source] Quantum chemical studies on molecular structural conformations and hydrated forms of salicylamide and O-hydroxybenzoyl cyanideINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 3 2005K. Anandan Abstract Ab initio and density functional theory (DFT) methods have been employed to study the molecular structural conformations and hydrated forms of both salicylamide (SAM) and O-hydroxybenzoyl cyanide (OHBC). Molecular geometries and energetics have been obtained in the gaseous phase by employing the Møller,Plesset type 2 MP2/6-311G(2d,2p) and B3LYP/6-311G(2d,2p) levels of theory. The presence of an electron-releasing group (SAM) leads to an increase in the energy of the molecular system, while the presence of an electron-withdrawing group (OHBC) drastically decreases the energy. Chemical reactivity parameters (, and ,) have been calculated using the energy values of the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) obtained at the Hartree,Fock (HF)/6-311G(2d,2p) level of theory for all the conformers and the principle of maximum hardness (MHP) has been tested. The condensed Fukui functions have been calculated using the atomic charges obtained through the natural bond orbital (NBO) analysis scheme for all the optimized structures at the B3LYP/6-311G(2d,2p) level of theory, and the most reactive sites of the molecules have been identified. Nuclear magnetic resonance (NMR) studies have been carried out at the B3LYP/6-311G(2d,2p) level of theory for all the conformers in the gaseous phase on the basis of the method of Cheeseman and coworkers. The calculated chemical shift values have been used to discuss the delocalization activity of the electron clouds. The dimeric structures of the most stable conformers of both SAM and OHBC in the gaseous phase have been optimized at the B3LYP/6-311G(2d,2p) level of theory, and the interaction energies have been calculated. The most stable conformers of both compounds bear an intramolecular hydrogen bond, which gives rise to the formation of a pseudo-aromatic ring. These conformers have been allowed to interact with the water molecule. Special emphasis has been given to analysis of the intermolecular hydrogen bonds of the hydrated conformers. Self-consistent reaction field (SCRF) theory has been employed to optimize all the conformers in the aqueous phase (, = 78.39) at the B3LYP/6-311G(2d,2p) level of theory, and the solvent effect has been studied. Vibrational frequency analysis has been performed for all the optimized structures at MP2/6-311G(2d,2p) level of theory, and the stationary points corresponding to local minima without imaginary frequencies have been obtained for all the molecular structures. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005 [source] Royal crown-shaped electride Li3 -N3 -Be containing two superatoms: New knowledge on aromaticityJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 8 2006Zhi-Ru Li Abstract The structure and aromaticity of a royal crown-shaped molecule Li3 -N3 -Be are studied at the CCSD(T)/aug-cc-pVDZ level. This molecule is a charge-separated system and can be denoted as Li32+N33,Be+. It is found that the Li32+ ring exhibits aromaticity mainly because the Li32+ ring can share the ,-electron with the N3,3 ring. The 4n+2 electron counter rule can be satisfied for the Li32+ subunit if the shared , valence electron of N33, subunit is also taken into account. This new knowledge on aromaticity of a ring from the interactions between subunits is revealed first time in this paper. Li3 -N3 -Be can be also regarded as a molecule containing two superatoms (Li3 and N3), which may be named as a "superomolecule." Li3 -N3 -Be is a new metal,nonmetal,metal type sandwich complex. The N33, trianion in the middle repulses the electron clouds of the two metal subunits (mainly to the Li3 superatom) to generate an excess electron, and thus Li3 -N3 -Be is also an electride. This phenomenon of the repulsion results in: (a) the HOMO energy level increased, (b) the electron cloud in HOMO distended, (c) the area of the negative NICS value extended, and (d) the VIE value lowered. So the superomolecule Li3 -N3 -Be is not only a new metal,nonmetal,metal type sandwich complex but also a new type electride, which comes from the interaction between the alkali superatom (Li3) and the nonmetal superatom (N3). © 2006 Wiley Periodicals, Inc. J Comput Chem 27: 986,993, 2006 [source] |