Orbital phase in Suzuki–Miyaura cross-coupling reactions

We investigated the electronic structures of the transition states of the oxidative addition, transmetalation, and reductive elimination steps in the catalytic cycle of the title reaction. The frontier orbital theory was surprisingly found to be applicable whereas any d orbitals of transition metals can be a main component of frontier orbitals because of their close energies. Visualizing the actually calculated HOMO and LUMO of the two parts of the transition structure of each step clearly demonstrated their orbital phase matching in favor of overlapping. The HOMO for the transmetalation step suggests that electron-donating ability of the carbon–metal bond of organometallic compounds (RMX) could control the reactivities of related cross-coupling reactions. The energies of the molecular orbitals having large amplitudes of the C–M bonding orbitals of RMX explain why the Suzuki–Miyaura cross-coupling reaction needs a base while the Kumada–Tamao and Negishi reactions take place without any bases.     

Maximum Overlap Symmetry Molecular Orbital Calculation under CNDO／2 Approximation

ＭａｘｉｍｕｍＯｖｅｒｌａｐＳｙｍｍｅｔｒｙＭｏｌｅｃｕｌａｒＯｒｂｉｔａｌＣａｌｃｕｌａｔｉｏｎｕｎｄｅｒＣＮＤＯ／２ＡｐｐｒｏｘｉｍａｔｉｏｎＹｅＳｈｉ－Ｙｏｎｇ；ＺｈａｎＣｈａｎｇ－Ｇｕｏ（ＤｅｐａｒｔｍｅｎｔｏｆＣｈｅｍｉｓｔｒｙ，Ｃｅｎｔｒ...     

通用轨道绘制软件Orbital Viewer及其在教学中的应用

以实例介绍了用轨道绘制软件OrbitalViewer制作原子、分子轨道 3D图形和VRML动画的方法 ,以及这些素材在网络课件和PowerPoint演示中的显示与播放方法     

Butadienyl Diiron Complexes: Nonplanar Metalla-Aromatics Involving σ-Type Orbital Overlap

A new class of nonplanar metalla-aromatics, diiron complexes bridged by a 1,3-butadienyl dianionic ligand, were synthesized in high yields from dilithio reagents and two equivalents of FeBr₂. The complexes consist of two antiferromagnetically coupled high-spin Fe^II centers, as revealed by magnetometry, Mössbauer spectroscopy, and DFT calculations. Furthermore, experimental (X-ray structural analysis) and theoretical analyses (NICS, ICSS, AICD, MOs) suggest that the complexes are aromatic. Remarkably, this nonplanar metalla-aromaticity is achieved by an uncommon σ-type overlap between the ligand p and metal d orbitals, in sharp contrast to the intensively studied planar aromatic systems featuring delocalized π-type bonding. Specifically, the σ-type interaction between the two Fe 3d_xz orbitals and the butadienyl π orbital results in the formation of a six-electron conjugated system and hence enables the aromatic character.     

Self-consistent Field Crystal Orbital Study on One-dimensional C_(60) Polymer

Ｓｅｌｆ┐ｃｏｎｓｉｓｔｅｎｔＦｉｅｌｄＣｒｙｓｔａｌＯｒｂｉｔａｌＳｔｕｄｙｏｎＯｎｅ┐ｄｉｍｅｎｓｉｏｎａｌＣ６０Ｐｏｌｙｍｅｒ＊ＨＵＡＮＧＹｕａｎ－ｈｅ＊＊,ＣＨＥＮＧｕａｎｇ－ｊｕａｎｄＬＩＵＲｕｏ－ｚｈｕａｎｇ（ＤｅｐａｒｔｍｅｎｔｏｆＣｈ...     

以Orbital Viewer为辅助实施原子轨道和共价键类型的互动性课堂

针对学生对于无机化学的微观结构部分内容学习过程中枯燥、难以形象化的具体情况，本文介绍了系列利用Orbital Viewer为辅助进行互动性课堂的教学活动。通过在原子轨道、共价键类型等知识点进行互动性教学活动的实施，能够有效提升学生学习积极性与动机，并建立合理的微观结构模型，掌握原子轨道、共价键的真实结构，为进一步学习杂化轨道、分子轨道理论奠定基础。     

Orbital Interaction of Epoxidation on the Same Curvature Bonds of Single-walled Carbon Nanotubes

The epoxidation of different bonds with the same bond curvature in one nano-tube including armchair,zigzag and chiral tubes was studied. The calculated results showed that for the adducts with opened C–O–C configuration,the magnitude of the binding energies was related with their corresponding bonding characteristics in HOMO,and the larger binding energies were attributed to stronger orbital interaction between one O atom and the nanotube; whereas for the adducts with 3MR structures,the binding energies were related with the changes of C–C bond length and independent of the frontier orbital interaction before and after epoxidation.     

Bonding Energy of a Molecular Orbital(Ⅱ)——Ab initio Calculation

Calculation of the bonding energy of a molecular orbital for a series of small molecules has been carried out by using ab initio STO-3G method. The results obtained demonstrate that the concept of the molecular orbital bonding energy is applicable for judging whether a molecular orbital is bonding, nonbonding or antibonding besides Mulliken overlap criterion.     

Theoretical Study on the Molecular Orbital and Stabilization Energy of Substituted Lithium Carbene Cations

Themetalcarbenecations,esPeciallytransitionmetalcarbenecations,areaclass0funstableintermediateswithhighactivity.TheyareveryimPortamtothefieldoforganometallicchendstryandhavegreatlyattractedchemist'sattention.JacobsonlstUdiedthereactionsofFeCH, andCoCH, withalkanes"',olefms2ingasphase.Butsofarasweknow,thereisnosystematictheoreticalstUdyontheirsmictUresandstability.InthispaPer,westUdythestfUcturalcharacteristics,molecularorbitalsofXCHLi andrelationshiPbetweensubstituelltsandstability,tak…     

Orbital phase control of the conformations of α- and β-substituted enamines and vinyl ethers

The conformational stabilities of the α- and β-substituted enamines and vinyl ethers were predicted by orbital phase theory and confirmed by ab initio molecular orbital calculations. Cyclic interaction significantly occurs among the nonbonding orbital n _Y for the lone pair on the hetero atom Y (N in the enamines or O in the ethers), the π and π* orbitals of the CC bond, and the σ_C-H or σ*_C-X orbitals on the substituent CH₂X. The cyclic -n _Y-π-σ_C-H-π*- interaction is favored by the orbital phase continuity in the α-substituted molecules, while the cyclic -n _Y-π-σ*_C-X-π*- interaction is favored in the β-substituted molecules. The most stable conformation was then predicted to be synperiplanar or (pseudo)equatorial in the α-substituted molecules and anticlinical or (pseudo)axial in the β-substituted molecules. Received: 8 May 1998 / Accepted: 30 July 1998 / Published online: 16 November 1998     

A PM3 Molecular Orbital Study on the Conformational Equilibrium of Cyclohexane upon α-Cyclodextrin Inclusion Complexation

The effect ofα-cyclodextrin (α-CD) inclusion complexation on the conformational equilibrium of cyclo- hexane wasstudied with thesemiempirical PM3 molecularorbital calculations. The calculation results indicated that the chair form of cyclohexane is 18.5 kJ·mol-1lower than that of boat one in energy, however, theα-cyclodextrin inclusion complex of boat cycl ohexane is 4.4 kJ·mol-1more stable than the complex of chair form. It demon-strated that the conformational equilibrium of cyclohexane was influenced by theα-CD inclusion complexation. Hence, caution should be given when extrapolating the conformational behaviors of the guest compounds in the supramolecular systems totheir free forms, since the interactionsbetween the host and guest significantly affect the conformation of the guest compounds.     

Octahedral and Tetrahedral Coinage Metal Clusters: Is Three‐Dimensional d‐Orbital Aromaticity Viable?

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.     

Crystal Structure and Molecular Orbital Calculation of（1R，2S）－N－Methylephedine Benzoate Hydrochloride

ＣｒｙｓｔａｌＳｔｒｕｃｔｕｒｅａｎｄＭｏｌｅｃｕｌａｒＯｒｂｉｔａｌＣａｌｃｕｌａｔｉｏｎｏｆ（１Ｒ，２Ｓ）－Ｎ－ＭｅｔｈｙｌｅｐｈｅｄｉｎｅＢｅｎｚｏａｔｅＨｙｄｒｏｃｈｌｏｒｉｄｅＣｈｅｎｇＸｉａｏ－Ｊｕｎ（ＥｎｖｉｒｏｎｍｅｎｔａｌＰｒｏｔｅ...     

Performance of Range Separated Density Functional in Solvent Continuum: Tuning Long-range Hartree–Fock Exchange for Improved Orbital Energies

Performance of the density functionals mainly depends on the proper approximation of exchange-correlation functionals. Modification of various parameters of such functionals, according to the demand of the system, has brought their accuracy level to a new height. Recent reports highlight that Long-range Corrected (LC) functionals are not encouraging in reproducing orbital energies in solvent. Therefore, in this article, we have proposed a tuning scheme for the LC functional for improved orbital energies. In this scheme, the optimized long-range HF exchange and the dielectric constant of the medium are included to modify the form of functionals. The proposed tuning is tested over a set of 103 molecules from IP131 database and fifteen solvent dielectrics. The tuned range separated functionals reproduce orbital eigenvalues in solvent continuum with good accuracy. More importantly, there is a consistency in the error for the tuned functional across the solvent media. © 2019 Wiley Periodicals, Inc.     

Evidence for d‐Orbital Aromaticity in Sn‐ and Pb‐Based Clusters: Is Sn2‐12 Aromatic?

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.