Stability analysis of the neutral noble gas molecules FNgX and their anions FNgX− (Ng = He,Ar, Kr; X = O,S)

The structural stability and bonding energies of the neutral noble gas molecules FNgX and their anions FNgX^? (Ng = He, Ar, Kr; X = O, S) are discussed at the CCSD(T)/aug‐cc‐pVnZ (n = D, T) levels. Results reveal that only two neutral FKrX molecules are stable, whereas their FHeX and FArX counterparts are not. All their anions are stable and the stability mainly derives from the contribution of the extra electron, i.e., the attachment of the electron greatly enhances the orbital interactions of two bonds, F? Ng and Ng? X. Different from the anion counterparts, the electrostatic interaction energy plays a crucial role in the FKrX stability. Compared with those unstable FHeX and FArX counterparts, the enough charge distribution over each atom of FKrX ensures the effective bonding between F and Kr, and between Kr and X, consequently strengthen the stability of the neutral FKrX (X = O, S) structures. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2009     

CH2=CHCl与O(3P)反应的理论研究

用量子化学密度泛函理论和QCISD(Quadratic configuration interaction calculation)方法,对0(^3P)与CH2CHCl的反应进行了理论研究．在UB3LYP／6—311 G(d,p),UB3LYP／6—31 (3df,3pd)计算水平上,优化了反应物、产物、中间体和过渡态的几何构型,并在UQCISD(T)／6—311 G(2df,2pO)水平上计算了单点能量．为了确证过渡态的真实性,在UB3LYP／6—311 G(3df,3pd)水平上进行了内禀坐标(IRC)计算和频率分析,并确定了反应机理．研究结果表明,反应主要产物为CH2CHO和Cl．     

The nature and energy characteristics of intramolecular hydrogen bonds in crystals

The review concerns the results of systematic X-ray diffraction studies of the electron density distribution in the crystals of compounds with strong intramolecular hydrogen bonds N-H...O, O-H...O, O-H...N, and N-H...S. The advantages of the topological analysis of the electron density distribution function in the analysis of the nature and estimation of the H-bond energies directly from experimental data are discussed. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 1–14, January, 2006.     

A monooxorhenium(V) complex with an unusually long Re=O bond: the structure of [ReOI2(ame)(PPh3)] (Hame=2-(2-aminophenyl)ethanol)

The complex [ReOI₂(ame)(PPh₃)] (Hame=2-(2-aminophenyl)ethanol) was prepared from trans-[ReOI₂(OEt) (PPh₃)₂] and Hame in benzene. It contains an unusually long Re=O bond (1.717(5)?Å) and a large trans O=Re–O (ethanolate) bond angle of 171.4(2)°.     

难熔固体MX(M=Sc,Ti,V;X=C,N,O)电子结构和力学性质的密度泛函研究

采用密度泛函方法对MX(M=Sc,Ti,V;X=C,N,O)固体的体相电子结构和力学性质进行了系统研究.计算结果表明,对于金属原子相同的同一系列化合物,氮化物具有最大的体模量;进一步的研究可知,随着外界压力的增大,化合物由NaCl构型向CsCl构型转变由易到难的顺序依次是氧化物、氮化物和碳化物.本文还首次用密度泛函方法系统地计算了各化合物的能带结构和态密度,并对该类型化合物的导电性能进行了探讨.     

Redox‐Active Ligand Assisted Catalytic Water Oxidation by a RuIV=O Intermediate

Water splitting is one of the most promising solutions for storing solar energy in a chemical bond. Water oxidation is still the bottleneck step because of its inherent difficulty and the limited understanding of the O?O bond formation mechanism. Molecular catalysts provide a platform for understanding this process in depth and have received wide attention since the first Ru‐based catalyst was reported in 1982. Ru^V=O is considered a key intermediate to initiate the O?O bond formation through either a water nucleophilic attack (WNA) pathway or a bimolecular coupling (I2M) pathway. Herein, we report a Ru‐based catalyst that displays water oxidation reactivity with Ru^IV=(O) with the help of a redox‐active ligand at pH 7.0. The results of electrochemical studies and DFT calculations disclose that ligand oxidation could significantly improve the reactivity of Ru^IV=O toward water oxidation. Under these conditions, sustained water oxidation catalysis occurs at reasonable rates with low overpotential (ca. 183 mV).     

A Germylene/Borane Lewis Pair and the Remarkable C=O Bond Cleavage Reaction toward Isocyanate and Ketone Molecules

A germylene/borane Lewis pair ( 2 ) was prepared from a 1,1‐carboboration of amidinato phenylethynylgermylene ( 1 ) by B(C₆F₅)₃. Compound 2 reacted with iPrNCO and (4‐MeOC₆H₄)C(O)Me, respectively, with cleavage of the C=O double bond. In the first instance, O and iPrNC insert separately into the Ge?B bond to yield a GeBC₂O‐heterocycle ( 3 ) and a GeBC₃‐heterocycle ( 4 ). In the second case (4‐MeOC₆H₄)(Me)C inserts into the Ge?N bond of 2 while O is incorporated in the Ge?B bond to form a Ge‐centered spiroheterocycle ( 5 ). The reaction of 2 with tBuNC to give 6 , which has almost the same structure as 4 , proved the formation of the isonitrile during transformation from 2 and iPrNCO to 3 and 4 . The kinetic study of the reaction of 2 and iPrNCO gave evidence of proceeding through a GeBC₃O‐heterocycle intermediate. In addition, a DFT study was performed to elucidate the reaction mechanism.     

A QTAIM-based energy partitioning for understanding the physical origin of conformational preferences: Application to the Z effect in O=C-X-R and related units

A quantum theory of atoms in molecules-based energy partitioning was carried out for Z and E conformers of a series of O=C-X-R containing compounds. The results obtained for the simplest compound (formic acid) indicate that the attraction of the electron density within carbonyl oxygen by the nucleus of the acid hydrogen is the most important energy term for Z preference. This conclusion can be extended (mutatis mutandis) to larger carboxylic acids, esters, sulfur derivatives, secondary amides, and carbonyl isocyanates, and even explains the sequence of relative conformational energies in the HCXOH series (X = O, S, Se). In contrast, although the hyperconjugative model has been traditionally employed to explain this preference, we observe it is incompatible with: (i) relative values of diverse QTAIM atomic populations for the Z / E conformational equilibrium; (ii) conformational energies in the HCXOH series. © 2012 Wiley Periodicals, Inc.     

On the vibrational structure involving C=O stretch in the vapour phase phosphorescence of p-benzoquinone-h4 and-d4

The high resolution spectrum of vapour phase phosphorescence fromp-benzoquinone exhibits a mixing of normal modes involving symmetric C=O stretching and C=C stretching vibrations. The vibrational bands due to these mixed vibrations have been assigned on the basis of relative intensities of these bands in the vapour phase and also, using solid neon host. On leave from Pt. Jawaharlal Nehru College, Banda 210001, India.     

An Isolable Silicon Analogue of a Ketone that Contains an Unperturbed Si=O Double Bond

Despite tremendous efforts to synthesize isolable compounds with an Si=O bond, silicon analogues of ketones that contain an unperturbed Si=O bond have remained elusive for more than 100 years. Herein, we report the synthesis of an isolable silicon analogue of a ketone that exhibits a three‐coordinate silicon center and an unperturbed Si=O bond, thus representing the first example of a genuine silanone. Most importantly, this silanone does not require coordination by Lewis bases and acids and/or the introduction of electron‐donating groups to stabilize the Si=O bond. The structure and properties of this unperturbed Si=O bond were examined by a single‐crystal X‐ray diffraction analysis, NMR spectroscopy, and theoretical calculations. Bimolecular reactions revealed high electrophilicity on the Si atom and high nucleophilicity on the O atom of this genuine Si=O bond.     

Nature of weak inter- and intramolecular interactions in crystals. 1. The F...O and F...H contacts in the crystal of 2-trifluoroacetyl-5-trifluoromethylpyrrole

The topological analysis of the electron density distribution in the crystal of 2-trifluoroacetyl-5-trifluoromethylpyrrole revealed that the F...H and F...O intermolecular contacts correspond to attractive interactions. The energies of these interactions were estimated from the experimental data and it was shown that these contacts are similar to the C—H...O contacts. Analysis of the deformation electron density revealed that the F...O contacts correspond to transfer of the lone electron pair of a fluorine atom to the antibonding -orbital of the C=O bond.     

QTAIM study of strong H-bonds with the O-H...a fragment (A=O, N) in three-dimensional periodical crystals

The relationship between the d(H...A) distance (A=O, N) and the topological properties at the H...A bond critical point of 37 strong (short) hydrogen bonds occurring in 26 molecular crystals are analyzed using the quantum theory of atoms in molecules (QTAIM). Ground-state wave functions of the three-dimensional periodical structures representing the accurate experimental geometries calculated at the B3LYP/6-31G** level of approximation were used to obtain the QTAIM electron density characteristics. The use of an electron-correlated method allowed us to reach the quantitatively correct values of electron density rhob at the H...A bond critical point. However, quite significant differences can appear for small absolute values of the Laplacian (<0.5 au). The difference between the H...O and H...N interactions is described using the rhob versus d(H...A) dependence. It is demonstrated that the values of parameters in this dependence are defined by the nature of the heavy atom forming the H...A bond. An intermediate (or transit) region separating the shared and closed-shell interactions is observed for the H-bonded crystals in which the bridging proton can move from one heavy atom to another. The crystalline environment changes the location of the bridging proton in strong H-bonded systems; however, the d(O-H)/d(H...O) ratio is approximately the same for both the gas-phase complexes and molecular crystals with a linear or near-linear O-H...O bond.     

DFT studies of ESR parameters for N?O centered radicals,N‐alkoxyaminyl and aminoxyl radicals

Theoretical calculations of ESR parameters for aminoxyl radicals have been widely studied using the density functional theory (DFT) calculations. However, the isomer N‐alkoxyaminyl radicals have been limitedly studied. With the use of experimental data for 46 N‐alkoxyaminyl and 38 aminoxyl radicals, the isotropic ¹⁴N hyperfine coupling constants (a_N) and g‐factors have been theoretically estimated by several DFT calculations. The best calculation scheme of a_N for N‐alkoxyaminyl radicals was PCM/B3LYP/6‐31 + + G(d,p) (R² = 0.9519, MAE = 0.034 mT), and that for aminoxyl radicals was PCM/BHandHLYP/6‐31 + + G(3df,3pd) (R² = 0.9336, MAE = 0.057 mT). For aminoxyl radicals, the solvation models in calculations enhanced the accuracy of reproducibility. In contrast, for N‐alkoxyaminyl radicals the calculations with solvation models provided no improvement. The differences in the best functionals between two types of radicals were thought to come from the contribution ratios of neutral and dipolar canonical structures in resonance forms. The a_N for N‐alkoxyaminyl radicals that were stabilized by small contribution of dipolar canonical structures could be precisely reproduced by B3LYP with only 20% HF exact exchange. In contrast, the a_N for aminoxyl radicals stabilized by large contribution of dipolar canonical structures was well reproduced by BHandHLYP with 50% HF exchange. The best calculation scheme of g‐factors was IEFPCM/B3LYP/6‐31 + G(d,p) (R² = 0.9767, MAE = 0.0001) for not only aminoxyl but also N‐alkoxyaminyl radicals. Copyright © 2011 John Wiley & Sons, Ltd.     

The reduction mechanism of the C=O group. Part 2. The electrochemical reduction of p-diacetylbenzene in aqueous medium

A detailed study of the electrochemical reduction of diacetylbenzene A in aqueous medium between H_o = −5 and pH 14 is presented. The reactants are strongly adsorbed, so that the reactions are of a surface nature. From H_o = −5 to pH 6, a global 2e⁻ reduction yielding an enediol-type intermediate occurs. Analysis using the theory of the square schemes with protonations at equilibrium shows that, up to pH 4, the reaction is controlled by the first electron uptake, the paths being successively H⁺e⁻ and e⁻H⁺. The elementary electrochemical surface rate constants are 9.6 × 10⁷ s⁻ and 1.2 × 10⁶ s⁻ for AH⁺ and A respectively. From pH 6 to 14, a le⁻ adsorption wave, corresponding to the formation of (a) monoradical(s), appears and is followed by a le⁻ wave due to the reduction of the radical(s). A dimerization occurs, due to the coupling A⁻ + AH, as in the case of the monocarbonyl compounds. The rate of this surface process, k_d = 5 × 10¹³ cm² mol⁻¹ s⁻¹, is markedly smaller than the rate of the homogeneous reaction obtained in alkaline ethanol by Savéant et al. for the coupling of the radicals of benzaldehyde, benzophenone and acetophenone.     

A density functional study on a biomimetic non-heme iron catalyst: insights into alkane hydroxylation by a formally HO-FeV=O oxidant

The reactivity of [HO-(tpa)Fe(V)=O] (TPA=tris(2-pyridylmethyl)amine), derived from O-O bond heterolysis of its [H(2)O-(tpa)Fe(III)-OOH] precursor, was explored by means of hybrid density functional theory. The mechanism for alkane hydroxylation by the high-valent iron-oxo species invoked as an intermediate in Fe(tpa)/H(2)O(2) catalysis was investigated. Hydroxylation of methane and propane by HO-Fe(V)=O was studied by following the rebound mechanism associated with the heme center of cytochrome P450, and it is demonstrated that this species is capable of stereospecific alkane hydroxylation. The mechanism proposed for alkane hydroxylation by HO-Fe(V)=O accounts for the experimentally observed incorporation of solvent water into the products. An investigation of the possible hydroxylation of acetonitrile (i.e., the solvent used in the experiments) shows that the activation energy for hydrogen-atom abstraction by HO-Fe(V)=O is rather high and, in fact, rather similar to that of methane, despite the similarity of the H-CH(2)CN bond strength to that of the secondary C-H bond in propane. This result indicates that the kinetics of hydrogen-atom abstraction are strongly affected by the cyano group and rationalizes the lack of experimental evidence for solvent hydroxylation in competition with that of substrates such as cyclohexane.     

Highly Chemoselective Reduction of Phosphine Oxides through Electrophilic Activation of the P=O Bond with Anhydride

A highly chemoselective reduction of phosphine oxides was demonstrated under transition-metal-free and alkaline reaction conditions. During the reaction, P=O bond was firstly electrophilically activated by an anhydride and subsequently reduced by the versatile and cheap NaH, which was strengthened by 15-crown-5. By this strategy, a variety of phosphine oxides including those bearing functional groups such as methyl, methoxyl, phenyl, fluorine, chlorine, bromine, iodine, trifluoromethyl, nitrile, ester, alkenyl, alkynyl and heterocycles were transformed readily into the corresponding phosphines in good to high yields. This work represents an efficient method for reducing phosphine oxides forming phosphines.     

不同沉淀剂对Co3O4催化剂催化分解N2O活性的影响

采用了不同沉淀剂（K2 CO3、Na2 CO3、NaOH、NaHCO3）制备了一系列 Co3 O4氧化物催化剂。通过 XRD、XPS、BET、H2-TPR、O2-TPD 表征手段,探究了催化剂物相结构和氧化还原性能对 N2 O 催化分解性能的影响。研究表明,以 K2 CO3为沉淀剂制备的 Co3 O4催化剂具有优越的氧化还原性能。此外,较低结晶度有助于提高催化剂的催化性能,催化剂表面物种与其沉淀剂相关：丰富的表面 Co 物种促进催化活性,较多氧空位有利于催化剂表面的电子传递和氧气的脱附。以 K2 CO3为沉淀剂制备的 Co3 O4催化剂表现出最佳的 N2 O 催化分解活性,在450℃达到90％以上的转化率。     

Theoretical Studies on the Intermonomer Interaction of F~-·(H_2O)_n (n = 1, 2)

1 INTRODUCTION Hydrogen bond plays an important role in the fields of physics, biology and chemistry. It has cap- tured the interest of chemists for a long time and reports about its theory and experiment have been well represented[1～6]. Concerning its theoretical inves- tigations, most of the emphases are placed on the weak interaction energy of intramolecular hydrogen bond. But studies on its spectrum behavior are rela- tively rare. These years spectrum behavior led by hydrogen bond h…     

O?O bond homolysis in hydrogen peroxide

O O bond homolysis in hydrogen peroxide (H₂O₂) has been studied using theoretical methods of four conceptually different types: hybrid DFT (B3LYP, M06‐2X), double‐hybrid DFT (B2‐PLYP), coupled‐cluster (CCSD(T)), and multiconfigurational (CASPT2). In addition, the effects of basis set size have also been analyzed. For all of these methods, the O O bond homolysis in hydrogen peroxide has been found to proceed through hydrogen bonded radical pair complexes. Reaction barriers for collapse of the radical pairs to hydrogen peroxide are minute, leading to an overall very flat potential energy surface. However, hydrogen bonding energies in the radical pair complex expressed as the energy difference to two separate hydroxyl radicals are sizeable and exceed 10 kJ/mol for all theoretical methods considered in this study. © 2017 Wiley Periodicals, Inc.     

Different orientations of C=O versus P=O in P(O)NHC(O) skeleton: the first study on an aliphatic diazaphosphorinane with a gauche orientation

Different orientations of P(O) versus C(O) in P(O)NHC(O) skeleton have been discussed in two new phosphorus(V)-nitrogen compounds with formula XP(O)Y and XP(O)Z₂ where X = NHC(O)C₆H₄(4-F) and Y = NHCH₂C(CH₃)₂CH₂NH (1), Z = NHC₆H₄(4-CH₃) (2). Compound 1 is the first example of an aliphatic diazaphosphorinane with a gauche orientation which has been studied by X-ray crystallography; the P=O bond is in the equatorial position of the ring. Both compounds show ⁿ J(F,C) and ^m J(F,H) coupling constants (n = 1, 2, 3 and 4; m = 3 and 4) and ³ J(P,C) > ² J(P,C). Quantum chemical calculations were performed with HF and Density Functional Theory (DFT) methods using 6−31+G(d,p) basis set. A tentative assignment of the observed vibrational bands for these molecules is discussed. Compound 1 shows a deshielded C atom of the carbonyl moiety (in ¹³C NMR spectrum) relative to that of 2, which is supported by IR spectroscopy in which the considerably lower C=O frequency is observed for 1. Comparing the X-ray crystallography and IR spectra of 1 and 2 shows that the acyclic compound 2, containing P=O and C=O bonds in an anti position, are involving in a stronger N–H···O=P hydrogen bond in crystal network. This leads to a weaker P=O and N_C(O)NHP(O)–H bonds and stronger N···O interaction. The N_amide–H is involved in an intramolecular N–H···O hydrogen bond.