Mechanism and origin of stereoselectivity in Robinson annulations leading to bicyclo[3.3.1]nonanes: a rare Curtin–Hammet scenario

Computational studies on the mechanism and diastereoselectivity of base catalyzed synthesis of bicyclo[3.3.1]nonanes by Robinson annulation are reported. Three possible mechanisms were considered, and only the methanol assisted H‐shift process could be the favorable pathway. We have discovered a rare Curtin–Hammet scenario: rate determining steps for the two diastereomeric products formed are completely different reactions, and a correction factor should be considered when gauging the ratio of products from competing pathways. The pathway leading to the anti product is kinetically preferred, which is consistent with experimental results. Finally, the ratio of the two products was rationalized. Copyright © 2016 John Wiley & Sons, Ltd.     

Mechanistic study on Mo(CO)6‐catalyzed intramolecular [2 + 2] or [2 + 2 + 1] cycloaddition reaction of 5‐allenyl‐1‐ynes

By means of density functional theory, the Mo(CO)₆‐catalyzed intramolecular [2 + 2] or [2 + 2 + 1] cycloaddition reaction of 5‐allenyl‐1‐ynes was investigated. All the intermediates and transition states were optimized completely at B3LYP/6‐311++G(d,p) level (LANL2DZ(f) for Mo). Calculations indicate that the complexation of 5‐allenyl‐1‐ynes with Mo(CO)₆ occurred preferentially at the triple bond to give the complex M1 and then the complexation with the distal double bond of the allenes generates the complex M5 . In this reaction, Mo(CO)₆‐catalyzed intramolecular [2 + 2] cycloaddition is more favorable than [2 + 2 + 1] cycloaddition. The reaction pathway Mo(CO)₆ + R → M5 → T7 → M12 → M13 → T11 → M18 → P4 is the most favorable one, and the most dominant product predicted theoretically is P4 . The solvation effect is remarkable, and it decreases the reaction energy barriers. Copyright © 2011 John Wiley & Sons, Ltd.     

A remarkable difference in the deprotonation steps of the Friedel–Crafts acylation and alkylation reactions

Friedel–Crafts acylation and alkylation reactions were investigated using density functional theory calculations. The reaction systems studied were (benzene + acetyl chloride + Al₂Cl₆ (or AlCl₃)) and (benzene + 2‐chloropropane + Al₂Cl₆). In the acylation reaction, the acylium ion intermediate is reached either via a Me? C(Cl)?O? Al₂Cl₆ complex or via direct Cl transfer: Me? C(?O)Cl? Al₂Cl₆ → Me? C?O^?+? Al₂Cl. The ion adds to benzene electrophilically to form a Wheland intermediate containing a strong C? H? Cl hydrogen bond, which leads to deprotonation and the subsequent formation of acetophenone. The resulting H? Cl? Al₂Cl₆ fragment is subjected to a nucleophilic attack by the carbonyl oxygen of the acetophenone, and recovery of the Al₂Cl₆ bridge is unlikely. Attack of the Al₂Cl₆ moiety by Me? C(Cl)?O gives the complex Me? C(Cl)?O–AlCl₃, whose reactivity toward acylation is similar to that of the Me? C(Cl)?O–Al₂Cl₆ complex. In the alkylation reaction, deprotonation does not take place, but rather a [1,2] H‐shift from the Wheland intermediate. The resulting α‐protonated cumene undergoes deprotonation, with subsequent recovery of the Al₂Cl₆ bridge. In addition, the Al₂Cl₆‐catalyzed isomerization of the n‐propyl to the isopropyl cation was found to be a dyotropic shift. Copyright © 2009 John Wiley & Sons, Ltd.     

A computational study of the thermolysis of β‐hydroxy ketones in gas phase and in m‐xylene solution

Theoretical calculations at the M05‐2X/6‐31+G(d) level of theory have been carried out in order to explore the nature of the mechanism of the thermal decomposition reactions of the β‐hydroxy ketones, 4‐hydroxy‐2‐butanone, 4‐hydroxy‐2‐pentanone, and 4‐hydroxy‐2‐methyl‐2‐pentanone in gas phase and in m‐xylene solution. The mechanism proposed is a one‐step process proceeding through a six‐membered cyclic transition state. A reasonable agreement between experimental and calculated activation parameters and rate constants has been obtained, the tertiary : secondary : primary alcohol rate constant ratio being calculated, at T = 503.15 K, as 5.9:4.7:1.0 in m‐xylene solution and 44.1:5.0:1.0 in the gas phase, compared with the experimental values, 3.7:1.3:1.0 and 13.5:3.2:1.0, respectively. The progress of the thermal decomposition reactions of β‐hydroxy ketones has been followed by means of the Wiberg bond indices. The lengthening of the O₁–C₂ bond with the initial migration of the H₆ atom from O₅ to O₁ can be seen as the driving force for the studied reactions. Calculated synchronicity values indicate that the mechanisms correspond to concerted and highly synchronous processes. The transition states are “advanced”, nearer to the products than to the reactants. Copyright © 2012 John Wiley & Sons, Ltd.     

MoO_3/Si界面区钼掺杂非晶氧化硅层形成的第一性原理研究

采用基于密度泛函理论的第一性原理计算方法,通过模拟MoO_3/Si界面反应,研究了MoO_x薄膜沉积中原子、分子的吸附、扩散和成核过程,从原子尺度阐明了缓冲层钼掺杂非晶氧化硅(a-SiO_x(Mo))物质的形成和机理.结果表明,在1500 K温度下, MoO_3/Si界面区由Mo, O, Si三种原子混合,可形成新的稳定的物相.热蒸发沉积初始时, MoO_3中的两个O原子和Si成键更加稳定,同时伴随着电子从Si到O的转移,钝化了硅表面的悬挂键. MoO_3中氧空位的形成能小于SiO_2中氧空位的形成能,使得O原子容易从MoO_3中迁移至Si衬底一侧,从而形成氧化硅层;替位缺陷中, Si替位MoO_3中的Mo的形成能远远大于Mo替位SiO_2中的Si的形成能,使得Mo容易掺杂进入氧化硅中.因此,在晶硅(100)面上沉积MoO_3薄膜时, MoO_3中的O原子先与Si成键,形成氧化硅层,随后部分Mo原子替位氧化硅中的Si原子,最终形成含有钼掺杂的非晶氧化硅层.     

Reactivities of acridine compounds in hydride transfer reactions

Reactivities of acridine derivatives (10‐benzylacridinium ion, 1a ⁺, 10‐methylacridinium ion, 1b ⁺, and 10‐methyl‐9‐phenylacridinium ion, 1c ⁺) have been compared quantitatively for hydride transfer reactions with 1,3‐dimethyl‐2‐substituted phenylbenzimidazoline compounds, 2Ha–h . Reactions were monitored spectrophotometrically in a solvent consisting of four parts of 2‐propanol to one part of water by volume at 25 ± 0.1 °C. Reduction potentials have been estimated for acridine derivatives by assuming that the equilibrium constants for the reductions of 1a ⁺ –c ⁺ by 2Hb would be the same in aqueous solution and accepting ?361 mV as the reduction potential of the 1‐benzyl‐3‐carbamoylpyridinium ion. The resulting reduction potentials, E, are ?47 mV for 1a ⁺, ?79 mV for 1b ⁺, and ?86 mV for 1c ⁺. Each of acridine derivatives gives a linear Brønsted plot for hydride transfer reactions. The experimental slopes were compared with those obtained by Marcus theory. This comparison shows that the kinetic data are consistent with a one‐step mechanism involving no high‐energy intermediates. Copyright © 2007 John Wiley & Sons, Ltd.     

DFT study the interaction of β‐cyclodextrin with benzyl azide and phenyl acetylene in synthesis of 1,2,3‐triazoles

The phenyl acetylene and benzyl azide cycloaddition reaction in water in the presence of β‐cyclodextrin (β‐CD) as a phase transfer catalyst (PTC) can get a better yield in a shorter time. The interaction between β‐CD and phenyl acetylene or benzyl azide plays an important role in this reaction. This paper studies the complexes of β‐CD with phenyl acetylene and benzyl azide using density functional theory (DFT) method. In order to find out the orientations of guests in the cavity of β‐CD, binding energy and deformation energy are investigated, and the calculated results are confirmed by ¹H nuclear magnetic resonance (¹HNMR). The data from single point energy indicate that the inclusion complexes can improve the solubilities of phenyl acetylene and benzyl azide in water. The ¹³C and ¹⁵N spectra show that the most obvious variation concentrates on C₆ and C₈ of phenyl acetylene and N₁₅ of benzyl azide in complexes. Mulliken charge and frontier orbital are employed for revealing the charge distribution. The effect of β‐CD is discussed in terms of the calculated parameters. Copyright © 2014 John Wiley & Sons, Ltd.     

Theoretical investigation and computational evaluation of overtone and combination features in resonance Raman spectra of polyenes and carotenoids

We review the theory for overtones and combinations in resonant Raman spectroscopy introduced by Nafie, Stein and Peticolas in 1971 on the basis of time‐ordered diagrams, and we apply it to β‐carotene with the support of density functional theory calculations. Comparison with experimental results obtained by Tasumi's group in 1994 is provided. The theory here presented allows a prompt evaluation of resonant Raman intensities with presently available quantum chemistry tools. Copyright © 2014 John Wiley & Sons, Ltd.     

Concentration‐dependent Raman study of noncoincidence effect in the NH2 bending and CO stretching modes of HCONH2 in the binary mixture (HCONH2 + CH3OH)

The isotropic and anisotropic parts of the Raman spectra of NH₂ bending and ν(CO) stretching modes of HCONH₂ in a hydrogen‐bonding solvent, methanol, at different concentrations have been analyzed carefully in order to study the noncoincidence effect (NCE). In neat HCONH₂, the experimentally measured values of noncoincidence Δν_nc are ∼11 and ∼18 cm⁻¹ for the NH₂ bending and ν(CO) stretching modes, which reduce to 0.45 and 1.14 cm⁻¹, respectively at the concentration of HCONH₂ in mole fraction, χ_m = 0.1. The experimental results have been explained on the basis of two models, namely, the microscopic prediction of Logan and the macroscopic model of Mirone and Fini. The relative success of the two models in explaining the experimental data for both the modes have been discussed. It has been observed that in case of the ν(CO) stretching vibrational mode the Logan model can reproduce the experimental data rather precisely, whereas in the case of the NH₂ bending mode, Mirone and Fini model yields more accurate results. Copyright © 2006 John Wiley & Sons, Ltd.     

Temperature‐dependent Raman spectroscopic studies of microstructure present in dipotassium molybdate crystals and their melts

Temperature‐dependent Raman spectra of K₂Mo_nO_3n+1 (n = 1, 2, 3) crystals up to and above their melting points were recorded, and their vibration modes in solid and molten states were assigned. Basic structural units and the corresponding cluster forms in molten dipotassium monomolybdates, dimolybdates, and trimolybdates were studied by in situ high‐temperature Raman spectroscopic studies together with theoretical calculations, including density functional theory and quantum chemistry ab initio calculation. Anion units of [MoO₄]²⁻, [Mo₂O₇]²⁻, and [Mo₃O₁₀]²⁻ were shown to principally exist in molten K₂MoO₄, K₂Mo₂O₇, and K₂Mo₃O₁₀, respectively. The mechanisms of the microstructural evolution of K₂Mo_nO_3n+1 (n = 1, 2, 3) crystals while being melted are schematically illustrated. Copyright © 2016 John Wiley & Sons, Ltd.     

Effect of an aliphatic spacer group on the adsorption mechanism on the colloidal silver surface of L‐proline phosphonodipeptides

A comparative study of molecular structures of five L ‐proline (L ‐Pro) phosphonodipeptides: L ‐Pro‐NH‐C(Me,Me)‐PO₃H₂ (P1), L ‐Pro‐NH‐C(Me,iPr)‐PO₃H₂ (P2), L ‐Pro‐L ‐NH‐CH(iBu)‐PO₃H₂ (P3), L ‐Pro‐L ‐NH‐CH(PA)‐PO₃H₂ (P4) and L ‐Pro‐L ‐NH‐CH(BA)‐PO₃H₂ (P5) has been carried out using Raman and absorption infrared techniques of molecular spectroscopy. The interpretation of the obtained spectra has been supported by density functional theory calculations (DFT) at the B3LYP; 6–31 + + G** level using Gaussian 2003 software. The surface‐enhanced Raman scattering (SERS) on Ag‐sol in aqueous solutions of these phosphonopeptides has also been investigated. The surface geometry of these molecules on a silver colloidal surface has been determined by observing the position and relative intensity changes of the Pro ring, amide, phosphonate and so‐called spacer (−R) groups vibrations of the enhanced bands in their SERS spectra. Results show that P4 and P5 adsorb onto the silver as anionic molecules mainly via the amide bond (∼1630, ∼1533, ∼1248, ∼800 and ∼565 cm⁻¹), Pro ring (∼956, ∼907 and ∼876 cm⁻¹) and carboxylate group (∼1395 and ∼909 cm⁻¹). Coadsorption of the imine nitrogen atom and PO group with the silver surface, possibly by formation of a weaker interaction with the metal, is also suggested by the enhancement of the bands at 1158 and 1248 cm⁻¹. P1, P2 and P3 show two orientations of their main chain on the silver surface resulting from different interactions of the  C CH₃,  NH and  CONH fragments with this surface. Bonding to the Ag surface occurs mainly through the imino atom (1166 cm⁻¹) for P2, while for P1 and P3 it occurs via the methyl group(s) (1194–1208 cm⁻¹). The amide group functionality (CONH) is practically not involved in the adsorption process for P1 and P2, whereas the C_s P bonds do assist in the adsorption. Copyright © 2008 John Wiley & Sons, Ltd.     

Comparison of adsorption mechanism on colloidal silver surface of alafosfalin and its analogs

This study reports the Raman (FT‐RS) and absorption infrared (FT‐IR) spectra, based on calculated wavenumbers and normal modes of vibrations, of the following compounds: L ‐Ala‐L ‐NH‐CH(Me)‐PO₃H₂ (alafosfalin, A1), L ‐Ala‐D ‐NH‐CH(Me)‐PO₃H₂ (A2), L ‐Ala‐L ‐NH‐CH(Et)‐PO₃H₂ (A3), D ,L ‐Ala‐D,L ‐NH‐CH(Et)‐PO₃H₂ (A4), L ‐Ala‐D ‐NH‐CH(iPr)‐PO₃H₂ (A5), L ‐Ala‐D,L ‐NH‐CH(iPr)‐PO₃H₂ (A6), L ‐Ala‐D,L ‐NH‐CH(tBu)‐PO₃H₂ (A7), L ‐Ala‐D,L ‐NH‐CH(iBu)‐PO₃H₂ (A8), L ‐Ala‐D,L ‐NH‐CH(cBu)‐PO₃H₂ (A9), L ‐Ala‐D,L ‐NH‐CH(nPA)‐PO₃H₂ (A10), β‐Ala‐D ‐NH‐CH(Me)‐PO₃H₂ (A11), and D,L ‐Ala‐NH‐C(Me,Me)‐PO₃H₂ (A12). The equilibrium geometries and vibrational wavenumbers are calculated using density functional theory (DFT) at the B3LYP; 6–31 + + G** level of theory using Gaussian'03, GaussSum 0.8, and GAR2PED software. We briefly compare and analyze the experimental and calculated vibrational wavenumbers in the range of 3600–400 cm⁻¹. In addition, Raman wavenumbers are compared to those from surface‐enhanced Raman scattering (SERS) for the phosphonodipeptides of alanine (Ala) adsorbed on a colloidal silver surface. The geometry of these molecules etched on the silver surface is deduce from the observed changes in both the intensity and breadth of Raman bands in the spectra of the bound vs free species. For example, A7, A8, A1, A3, and A4 appear to adsorb onto the colloidal silver particles mainly through the phosphonate terminus, and for A3 and A4, through the  C‐NH₂ and  CONH fragments. The most dominant SERS bands of A5, A6, A9, A10, and A11 are due to the amide bond vibrations, as well as to the vibrations of the  C‐NH₂ group (A9 and A10) and the C C group (A6 and A11). The differences recorded for the A5, A6, A9, A10, and A11 and those of A2 and A12 are due to interactions between the amine and methyl groups with the silver surface, and they reflect vibrational characteristic of these groups. Copyright © 2008 John Wiley & Sons, Ltd.     

Existence of different intermediate Hamiltonians in type A -fold supersymmetry

Type A -fold supercharge admits a one-parameter family of factorizations into product of first-order linear differential operators due to an underlying symmetry. As a consequence, a type A -fold supersymmetric system can have different intermediate Hamiltonians corresponding to different factorizations. We derive the necessary and sufficient conditions for the latter system to possess intermediate Hamiltonians for the case. We then show that whenever it has (at least) one intermediate Hamiltonian, it can admit second-order parasupersymmetry and a generalized 2-fold superalgebra. As an illustration, we construct a set of generalized Pöschl–Teller potentials of this kind.