Photoelectron spectroscopy of carbonyls. Bicyclo[2.2.1]-heptane-2,3-diones and bicyclo [2.2.1] hept-5-ene-2,3-diones

The HeI photoelectron spectra (UPS) of several bicyclo [2.2.1] heptane-2,3-diones and bicyclo[2.2.1] hept-5-ene-2,3-diones are presented. Interpretations are based on CNDO/s computations and empirical correlations. The n₊ orbital of the two carbonyl groups interacts strongly with, the π orbital of the 5-ene moiety in bicyclo[2.2.1]hept-5-ene-2,3-diones. This interaction is dominantly “through-bond”, there being little or no direct (i.e. “through-space”) overlap. The net result is that insertion of 5-ene unsaturation increases the splitting of the n₊ and n_? orbitals from ca. 1.9 to ca. 2.4 eV. Finally, the π* (CO) ← n₊ electronic absorption spectra of the [5-ene] -compounds, which are geometrically suited to an investigation of π/π* (CO) interactions, suggest that such mixing is negligible.     

Probing the rotational disorder of molecules in plastic bicyclo[2.2.1]hept-2-ene with implanted muons

We report on μSR radical experiments on bicyclo[2.2.1]hept-2-ene, which demonstrate a dramatic change in the reorientational dynamics of the molecules throughout the plastic mesophase. The data might be related to some “order parameter” which is large at low temperature, while it is reduced almost by an order of magnitude (though it is still non-zero) close to the melting point.     

Microwave spectrum,structure, and dipole moment of bicyclo[3.1.0]hex-2-ene

The microwave spectra of the normal and four monosubstituted ¹³C isotopic species of bicyclo[3.1.0]hex-2-ene have been observed and analyzed. For the normal species the rotational constants (in megahertz) are: Λ = 6306.121 ± 0.006, B = 4516.667 ± 0.004, C = 3208.823 ± 0.002. From the complete data set, a partial r_s heavy-atom structure has been obtained as well as a complete effective structure. The r_s distances are found to be C₁C₅ = 1.521 ± 0.001 Å, C₁C₂ = 1.494 ± 0.010 Å, C₅C₆ = 1.482 ± 0.006 Å, C₁C₆ = 1.522 ± 0.007 Å. The overall effective structure shows the five-membered ring to be only slightly nonplanar (by ca. 6°), and the three-membered ring to be rather sharply inclined with respect to the five-membered ring (dihedral angle C₁C₅C₆-C₁C₅C₄ = 113.5°). Dipole moment measurements for the symmetryless molecule yielded values of |μ_a| = 0.166 ± 0.009, |μ_b| = 0.209 ± 0.015, |μ_c| = 0.119 ± 0.001, |μ_T| = 0.292 ± 0.012 D.     

Microwave spectrum,structure, and dipole moment of 7-oxabicyclo[2.2.1]heptane

The microwave spectrum of 7-oxabicyclo[2.2.1]heptane has been assigned in the ground and two excited vibrational states. Relative intensity measurements indicate that these two vibrations have wavenumbers of 120(30) and 330(30) cm^?1. The dipole moment obtained from Stark effect measurements is 1.621(10) D. The molecule is shown to have C_2v symmetry and the assignment of the two singly substituted ¹³C species gives the following skeletal structure: C₁-C₂ = 1.537(5) Å; C₂-C₃ = 1.551(5) Å; C₁-O = 1.452(10) Å; ?C₁OCC₄ = 95.3(10)° φ = 113.1(5)°.     

Reaction of bicyclo[2.2.1]hept‐5‐ene‐endo‐2‐ylmethylamine and nitrophenyl glycidyl ethers

Reactions of 2‐nitro‐, 4‐nitro‐ and 2,4‐dinitrophenylglycidyl ethers with bicyclo[2.2.1]hept‐5‐ene‐endo‐2‐ylmethylamine in isopropanol have been studied. The mixtures of products were chromatographed on silica gel and eluted with ether or ether/2‐propanol (1:1), the structures of individual products have been confirmed by IR spectra, NMR ¹H, ¹³C spectra, using experiments that involve homonuclear and heteronuclear scalar coupling interactions (COSY, TOCSY, HMQC, HMBC), and mass spectrometry. Amino alcohols as the major products of regioselective aminolysis of epoxides (according to the Krasusky rule) have been obtained. The minor products were the compounds with two hydroxyalkyl fragments at the nitrogen atom. In case of dinitrophenylglycidyl ether, it was the minor product of aryl nucleophilic substitution (S_NAr). The abnormal course of aminolysis has been confirmed by the results of quantum‐chemical calculations of activation barries and Free Gibbs energies of the competitive reactions of epoxides (at the B3LYP/6‐311 + G(d,p) level of theory). Copyright © 2010 John Wiley & Sons, Ltd.     

Study of the [Fe(OMe)(dpm)2]2 dimer in the presence of a magnetic field by using Mössbauer spectroscopy

We present a Mössbauer study of a S = 0 ground state magnetic Fe(III)-dimer in the presence of an applied 5 T longitudinal magnetic field, between 7.6 and 33 K. The values obtained for the isomer shift and the quadrupolar splitting are comparable with the ones of Fe(III) ions coordinated to eight oxygen ions. Regarding the spin dynamics, both intramultiplet and intermultiplet transitions are considered. In the chosen temperature range the rate of the former transitions is constant, within the errors, while the rate of the latter ones quickly increases with the temperature.     

Ultrasound assisted synthesis of tetrahydrobenzo[c]xanthene-11-ones using CAN as catalyst

Tetrahydrobenzo[c]xanthenes-11-ones was synthesized by a three component reaction of α-naphthol, aromatic aldehyde and dimedone. Ceric ammonium nitrate acts as a suitable eco-friendly catalyst for this method. Shorter reaction duration, mild reaction condition and low cost make this protocol more effective.     

Calculated polar substituent effects on the stability of 3‐substituted(X) bicyclo[1.1.1]pent‐1‐yl cations and 4‐substituted(X) bicyclo[2.2.1]hept‐1‐yl cations: a DFT study

The effects of substituents on the stability of 3‐substituted(X) bicyclo[1.1.1]pent‐1‐yl cations (3) and 4‐substituted(X) bicyclo[2.2.1]hept‐1‐yl cations (4), for a set of substituents (X = H, NO₂, CN, NC, CF₃, CHO, COOH , F, Cl, HO, NH₂, CH₃, SiH₃, Si(CH₃)₃, Li, O^?, and NH₃⁺) covering a wide range of electronic substituent effects were calculated using the DFT theoretical model at the B3LYP/6‐311 + G(2d,p) and B3LYP/6‐31 + G (d) levels of theory, respectively. Linear regression analysis was employed to explore the relationship between the calculated relative hydride affinities (ΔE, kcal/mol) of the appropriate isodesmic reactions for 3/4 and polar field/group electronegativity substituent constants (σ_F and σ_χ, respectively). The analysis reveals that the ΔE values for both systems are best described by a combination of both substituent constants. The result highlights the importance of the σ_χ dependency of charge delocalization in these systems. Copyright © 2012 John Wiley & Sons, Ltd.     

Magnetic order in LaEuSrCuO studied [2pt] by Fe Mössbauer spectroscopy

⁵⁷Fe M?ssbauer effect studies of La_1.65Eu_0.20Sr_0.15CuO₄ doped with 0.5 at% ⁵⁷Fe performed in the temperature region 300 K > T > 4.2 K give an onset temperature for magnetic ordering of K. This temperature practically is the same as that found in Nd doped La_2-xSr_xCuO₄. It indicates that the magnetic ordering temperature in the LTT phase of rare earth (RE) doped La_2-xSr_xCuO₄ is independent of the RE moment. The direction of the ⁵⁷Fe magnetic moment in the magnetically ordered state is within the CuO₂ plane, while it has been found to be parallel to the c-axis in Nd doped La_2-xSr_xCuO₄. Received: 23 June 1998 / Accepted: 14 July 1998     

Determination of the chiral structure of [Formula: see text] using anomalous x-ray scattering near the Cs K absorption edge

A structural study of [Formula: see text], grown from aqueous solution, was performed using anomalous x-ray scattering near the Cs K absorption edge to determine an absolute configuration of constituent atoms. The sense of the helical structure of the [Formula: see text] chain was found to be predominantly right-handed through a comparison of observed Bragg Bijvoet ratios with calculated ones. Assuming that [Formula: see text] consists of the two domains (i.e. right- and left-handed helices), we estimate that the volume fraction for the right-handed helix is [Formula: see text].     

Analysis of the electronic structure of ZrO2 by Compton spectroscopy

The electronic structure of ZrO₂ is studied using the Compton scattering technique. The first-ever Compton profile measurement on polycrystalline ZrO₂ was obtained using 59.54 keV gamma-rays emanating from the ²⁴¹Am radioisotope. To explain the experimental data, we compute theoretical Compton profile values using the method of linear combination of atomic orbitals in the framework of density functional theory. The correlation scheme proposed by Perdew-Burke-Ernzerhof and the exchange scheme of Becke are considered. The ionic-model-based calculations for a number of configurations, i.e., Zr^+x (O^?x/2)₂ (0 ≤ x ≤ 2), are also performed to estimate the charge transfer on compound formation, and the study supports transfer of 1.5 electrons from Zr to O atoms.     

靶丸内表面轮廓的白光共焦光谱测量技术

靶丸内表面轮廓是激光核聚变靶丸的关键参数,需要精密检测。本文首先分析了基于白光共焦光谱和精密气浮轴系的靶丸内表面轮廓测量基本原理,建立了靶丸内表面轮廓的白光共焦光谱测量方法。此外,搭建了靶丸内表面轮廓测量实验装置,建立了基于靶丸光学图像的辅助调心方法,实现了靶丸内表面轮廓的精密测量,获得了准确的靶丸内表面轮廓曲线;最后,对测量结果的可靠性进行了实验验证和不确定度分析,结果表明,白光共焦光谱能实现靶丸内表面低阶轮廓的精密测量,其测量不确定度优于0.1μm。     

Determination of fine structure intervals in a series of excited sodium D states using doppler free two-photon spectroscopy

Using Doppler free two-photon spectroscopy technique, we have measured the absolute values of fine-structure (fs) intervals in a series of excited sodium n²D states (n = 3,6,7, and 8). We have shown the structures are inverted and our measured values for these states are: Δ_fs(3²D) = -1523 ± 8 MHz, Δ_fs(6²D) = -385 ± 5 MHz, Δ_fs(7²D) = -253 ± MHz, and Δ_fs(8²D) = -173 ± 10 MHz.     

Modulated structure of the superconducting phases in Pb-modified Bi[sbnd]Sr[sbnd]Ca[sbnd]Cu[sbnd]O

Abstract

High resolution electron microscopy has shown that a modulated structure occurs in the Bi[sbnd]Sr[sbnd]Ca[sbnd]Cu[sbnd]O system. Electron diffraction and x-ray diffraction observations show that this modulation produces extra reflections. Diffraction patterns of the Pb-free material have superstructure reflections with wave vectors [0, 1/4.7, 1] and [0, ?1/4.7, 1]. These two waves vectors can generate all of the superstructure relections associated with each fundamental reflection. When PbO is added to the BSCCO system a new wave vector [0. 1/8.5, 0] is introduced. Observations show that within a single grain the two wave vectors coexist for a Pb and Bi ratio of about 0.25. This produces a non-uniform modulated structure which may be due to a superposition of the two wave vectors. The intensity of the [0, 1/4.7, 1] wave vector is substantially reduced in the Pb-modified material. The b' component of both wave vectors in incommensurate with the lattice period. The same superstructures occurs in both the low-T_c phase and the high-T_c phase.     

Study on the binding of 2,3-diazabicyclo[2.2.2]oct-2-ene with bovine serum albumin by fluorescence spectroscopy

The interaction of 2,3-diazabicyclo[2.2.2]oct-2-ene (DBO) with bovine serum albumin (BSA) has been studied using absorption and steady state fluorescence techniques. Fluorescence spectrum of BSA (λ_exi=280 nm) in the presence of DBO clearly shows that DBO acts as a quencher. The number of binding sites ‘n’ and apparent binding constant ‘K’ were measured by Stern-Volmer equation. Synchronous fluorescence and absorption spectra were used to study protein conformation. The interaction between DBO and BSA is consistent with static quenching and the conformational changes of BSA observed.     

Degenerate thermal isomerizations of bicyclo[3.1.1]hept‐2‐ene: strategy and analysis

Bicyclo[3.1.1]hept‐2‐ene was first prepared and well identified in 1972. In 1974, the degenerate thermal isomerization involving 1‐d‐ and 3‐d‐bicyclo[3.1.1]hept‐2‐ene was approached successfully, as one of the two deuterium‐labeled structures was selected, heated, and equilibrated. There has been no further study of this degenerate isomerization. Here, a detailed outline of reaction trajectories for d₂‐labeled bicyclo[3.1.1]hept‐2‐enes is given that will establish the four independent kinetic parameters needed for 20 linking paths between six d₂‐species. The use of racemates, eliminating chiral separations and dissections, provides degenerate isomerization paths providing this method with general utility. Copyright © 2014 John Wiley & Sons, Ltd.     

匀浆提取-气相色谱/质谱联用法测定卷烟主流烟气中的苯并[a]芘

研究了用匀浆提取-气相色谱/质谱联用法测定卷烟主流烟气中苯并[a]芘的方法,卷烟主流烟气样品用剑桥滤片捕集,匀浆法提取滤片上捕集的苯并[a]芘,然后采用气相色谱-质谱联用法进样分析.结果显示该方法检测出的苯并[a]芘含量和国家标准相符合,并具有提取完全、效率高、能耗低的特点.