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NBO Analysis (nbo + analysis)
Selected AbstractsStable N-Heterocyclic Carbene Adducts of Arylchlorosilylenes and Their Germanium HomologuesCHEMISTRY - A EUROPEAN JOURNAL, Issue 9 2010Alexander Abstract The first N-heterocyclic carbene adducts of arylchlorosilylenes are reported and compared with the homologous germanium compounds. The arylsilicon(II) chlorides SiArCl(Im-Me4) [Ar=C6H3 -2,6-Mes2 (Mes=C6H2 -2,4,6-Me3), C6H3 -2,6-Trip2 (Trip=C6H2 -2,4,6- iPr3)] were obtained selectively on dehydrochlorination of the arylchlorosilanes SiArHCl2 with 1,3,4,5-tetramethylimidazol-2-ylidene (Im-Me4). The analogous arylgermanium(II) chlorides GeArCl(Im-Me4) were prepared by metathetical exchange of GeCl2(Im-Me4) with LiC6H3 -2,6-Mes2 or addition of Im-Me4 to GeCl(C6H3 -2,6-Trip2). All compounds were fully characterized. Density functional calculations on ECl(C6H3 -2,6-Trip2)(Im-Me4), where E=Si, Ge, at different levels of theory show very good agreement between calculated and experimental bonding parameters, and NBO analyses reveal similar electronic structures of the two aryltetrel(II) chlorides. The low gas-phase Gibbs free energy of bond dissociation of SiCl(C6H3 -2,6-Trip2)(Im-Me4) (,=28.1,kJ,mol,1) suggests that the carbene adducts SiArCl(Im-Me4) may be valuable transfer reagents of the arylsilicon(II) chlorides SiArCl. [source] Cubane-Like Bismuth-Iron Cluster: Synthesis, X-ray Crystal Structure and Theoretical Characterization of the [Bi4Fe8(CO)28]4, AnionEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 20 2010Kirill Yu. Abstract The reaction of cyclo -Bi4[Si(SiMe3)3]4 (1) with Na2[Fe(CO)4] in the presence of nBu4NCl leads to the formation of the cage compound [nBu4N]4[Bi4Fe8(CO)28] (2). According to X-ray single-crystal structure analysis, the faces of the tetrahedral Bi4 core are capped by Fe(CO)3 moieties in a ,3 fashion to give a cubanoid Bi4Fe4 framework. The four Fe(CO)4 fragments are ,1 -coordinated to bismuth, each. With 12 skeletal electron pairs the [Bi4Fe8(CO)28]4, anion (2a) is a Bi4Fe4 cubane. The negative charge is localized within cluster 2a according to the NBO analysis of its derivatives. The strength of metal,ligand interactions Bi,,3 -Fe(CO)3 is responsible for the size of the cluster's cubic core. NICS computations at the cage centers of considered molecules show that 2a has paratropic character, whereas removal of four ,1 -Fe(CO)4 fragments from latter causes spherical aromaticity of the modified clusters [Bi4Fe4(CO)12]4, (2aa) and [Bi4Fe4(CO)12]2+ (2ab), mediated by a Bi4 cluster , orbital. [source] Hydrogen bond of radicals: Interaction of HNO with HCO, HNO, and HOOINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 6 2010Yong Yang Abstract Ab initio quantum mechanics methods are employed to investigate hydrogen bonding interactions between HNO and HCO, HOO radicals, and closed-shell HNO. The systems were calculated at MP2/6-311++G (2d, 2p) level and G2MP2 level. The topological and NBO analysis were investigated the origin of hydrogen bonds red- or blue-shifts. In addition, the comparisons were performed between HNO-opened-shell radical (HCO, HOO) complexes and HNO-corresponding closed-shell molecule (H2CO, HOOH) complexes. It is found that the stabilities of complexes increase from HNO-HCO to HNO-HOO. There are blue-shifts of NH, CH stretching vibrational frequencies and a red-shift of OH stretching vibrational frequency in the complexes. Rehybridization and electron density redistribution contribute to the blue-shifts of CH and NH stretching vibrational frequencies. Compared with the closed-shell H2CO, HCO is weaker proton donor and weaker proton acceptor. For the HOO, it is stronger proton donor and weaker proton acceptor than the HOOH is. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010 [source] Intra and intermolecular hydrogen bonding in formohydroxamic acid,INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 1 2008Damanjit Kaur Abstract The presence of hydrogen bonding interactions in several tautomeric forms of formohydroxamic acid (FHA) and 1:1 association among the tautomeric forms and water-coordinated tautomeric forms of FHA is explored theoretically. Out of the seven equilibrium structures, four tautomeric forms have been selected for aggregation with single water molecule and dimer formation. Fifteen aggregates of FHA with H2O have been optimized at MP2/AUG-cc-PVDZ level and analyzed for intramolecular and intermolecular H-bond interactions. Twenty-seven dimers of the four tautomeric forms have been obtained at MP2/6-31+G* level. The stabilization energies associated with dimerization and adduct formation with water are the result of H-bond interactions and range from very weak to medium. The atomic charges and NBO analysis indicate that the electrostatic and the charge transfer are the important components favoring H-bond formation. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2008 [source] Blue-shifted H-bond in aromatic sulfines: An ab initio calculationINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 7 2007H. Roohi Abstract The intramolecular CH···OS H-bond in the aromatic sulfines, HRCSO, was analyzed by NBO and QTAIM methods. The results of QTAIM analysis at the MP2/aug-cc-pVDZ level of theory show that the CH···OS H-bond meets all the characteristics of an improper, blue shift hydrogen bond. NBO analysis at the MP2/6,31++G(d,p)//MP2/aug-cc-pVDZ level predicts a normal relationship between change of bond length and CH rehybridization. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2007 [source] Blue-shifted and red-shifted hydrogen bonds: Theoretical study of the CH3CHO· · ·HNO complexesINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 5 2006Yong Yang Abstract The blue-shifted and red-shifted H-bonds have been studied in complexes CH3CHO,HNO. At the MP2/6-31G(d), MP2/6-31+G(d,p) MP2/6-311++G(d,p), B3LYP/6-31G(d), B3LYP/6-31+G(d,p) and B3LYP/6-311++G(d,p) levels, the geometric structures and vibrational frequencies of complexes CH3CHO,HNO are calculated by both standard and CP-corrected methods, respectively. Complex A exhibits simultaneously red-shifted CH,O and blue-shifted NH,O H-bonds. Complex B possesses simultaneously two blue-shifted H-bonds: CH,O and NH,O. From NBO analysis, it becomes evident that the red-shifted CH,O H-bond can be explained on the basis of the two opposite effects: hyperconjugation and rehybridization. The blue-shifted CH,O H-bond is a result of conjunct CH bond strengthening effects of the hyperconjugation and the rehybridization due to existence of the significant electron density redistribution effect. For the blue-shifted NH,O H-bonds, the hyperconjugation is inhibited due to existence of the electron density redistribution effect. The large blue shift of the NH stretching frequency is observed because the rehybridization dominates the hyperconjugation. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2006 [source] DFT study and NBO analysis of the mutual interconversion of cumulene compoundsJOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 5 2007Davood Nori-Shargh Abstract The B3LYP/6-31G* method was used to investigate the configurational properties of allene (1,2-propadiene) (1), 1,2,3-butatriene (2), 1,2,3,4-pentateriene (3), 1,2,3,4,5-hexapentaene (4), 1,2,3,4,5,6-heptahexaene (5), 1,2,3,4,5,6,7-octaheptaene (6), 1,2,3,4,5,6,7,8-nonaoctaene (7), and 1,2,3,4,5,6,7,8,9-decanonaene (9). The calculations at the B3LYP/6-31G* level of theory showed that the mutual interconversion energy barrier in compounds 1,8 are: 209.73, 131.77, 120.34, 85.00, 80.91, 62.19, 55.56, and 46.83,kJ,mol,1, respectively. The results showed that the difference between the average CC double bond lengths () values in cumulene compounds 1 and 2, is larger than those between 7 and 8, which suggest that with large n (number of carbon atoms in cumulene chain), the values approach a limiting value. Accordingly, based on the plotted data, the extrapolation to n,=,,, gives nearly the same limiting (i. e., ). Also, NBO results revealed that the sum of , -bond occupancies, , decrease from 1 to 8, and inversely, the sum of , -antibonding orbital occupancies, , increase from compound 1 to compound 8. The decrease of values for compounds 1,8, is found to follow the same trend as the barrier heights of mutual interconversion in compounds 1,8, while the decrease of the barrier height of mutual interconversion in compounds 1,8 is found to follow the opposite trend as the increase in the number of carbon atom. Accordingly, besides the previously reported allylic resonant stabilization effect in the transition state structures, the results reveal that the values, , ,(EHOMO,,,ELUMO), and the C atom number could be considered as significant criteria for the mutual interconversion in cumulene compounds 1,8. This work reports also useful predictive linear relationships between mutual interconversion energy barriers () in cumulene compounds and the following four parameters: , , ,(EHOMO,,,ELUMO), and CNumber. Copyright © 2007 John Wiley & Sons, Ltd. [source] Theoretical studies on the S,N interaction in sulfinamidesJOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 4 2002Prasad V. Bharatam Abstract The potential energy surface of sulfinamide H(O)S,NH2 (1) was searched, using ab initio and density functional methods, to study the conformational preferences. High-accuracy G2MP2 calculations showed that the S,N rotational barrier in 1 is 7.0,kcal,mol,1. The inversion around N in 1 goes through a very low energy barrier. Charge analysis using the NPA method was performed to elucidate the electronic factors responsible for the observed trends in the S,N interactions. The strength of negative hyperconjugation in 1 was estimated using NBO analysis and by studying the substituent effect. The repulsions between the lone pairs on oxygen and nitrogen and the nN , ,*S,O negative hyperconjugation play an important role in the conformations. Copyright © 2002 John Wiley & Sons, Ltd. [source] Coadsorption of trimethyl phosphine and thiocyanate on colloidal silver: a SERS study combined with theoretical calculationsJOURNAL OF RAMAN SPECTROSCOPY, Issue 4 2009Gengshen Hu Abstract The adsorption of trimethyl phosphine (TMP) on colloidal silver has been investigated by means of surface-enhanced Raman scattering spectroscopy (SERS). On the basis of surface selection rules, it is deduced from the SERS results that TMP adsorbs on silver surface via its P atom. The electron donor effect of TMP can be sensitively probed by the coadsorbed SCN,. The Raman wavenumber of ,CN of the adsorbed SCN, shifts to lower wavenumbers when TMP is coadsorbed with SCN, and the red shift of C,N stretching wavenumber is found to increase with increasing surface coverage of TMP. This could be explained in terms of the electron donor effect of TMP. Density functional theory (DFT) calculations further confirm the experimental results that the charge transfer is from TMP to silver surface rather than reversely. Natural bond orbital (NBO) analysis indicates that the red shift of C,N stretching mode is due the increase of electronic populations of ,* orbital of C,N bond induced by coadsorbed TMP, consequently the C,N bond is weakened, and the ,CN shifts to lower wavenumbers. An NBO analysis also indicates that the conjugated effect between S atom and C,N bond could easily make the charge transfer from silver surface to C,N bond. Copyright © 2008 John Wiley & Sons, Ltd. [source] AIM and NBO analysisMAGNETIC RESONANCE IN CHEMISTRY, Issue 9 2010In the series of diaminoenones, large high-frequency shifts of the 1H NMR of the NH group in the cis -position relative to the carbonyl group suggests strong NH···O intramolecular hydrogen bonding comprising a six-membered chelate ring. The NH···O hydrogen bond causes an increase of the 1J(N,H) coupling constant by 2,4 Hz and high-frequency shift of the 15N signal by 9,10 ppm despite of the lengthening of the relevant NH bond. These experimental trends are substantiated by gauge-independent atomic orbital and density functional theory calculations of the shielding and coupling constants in the 3,3-bis(isopropylamino)-1-(aryl)prop-2-en-1-one (12) for conformations with the Z - and E -orientations of the carbonyl group relative to the NH group. The effects of the NH···O hydrogen-bond on the NMR parameters are analyzed with the atoms-in-molecules (AIM) and natural bond orbital (NBO) methods. The AIM method indicates a weakening of the NH···O hydrogen bond as compared with that of 1,1-di(pyrrol-2-yl)-2-formylethene (13) where NH···O hydrogen bridge establishes a seven-membered chelate ring, and the corresponding 1J(N,H) coupling constant decreases. The NBO method reveals that the LP(O) ,,*NH hyperconjugative interaction is weakened on going from the six-membered chelate ring to the seven-membered one due to a more bent hydrogen bond in the former case. A dominating effect of the NH bond rehybridization, owing to an electrostatic term in the hydrogen bonding, seems to provide an increase of the 1J(N,H) value as a consequence of the NH···O hydrogen bonding in the studied diaminoenones. Copyright © 2010 John Wiley & Sons, Ltd. [source] | ||||||||||