Vibrational Frequencies of 1,4-Dithiane-1-oxide (DTMSO)

Abstract

The Raman and infrared spectra of 1,4-dithiane-1-oxide are reported in the frequency region from 4000 to 130 cm^?1, for polycrystall ine samples. The observed bands are assigned on the assumption of a Cs chair form with axial conformation. The fundamental frequencies are discussed and compared with those of 1,4-dithiane, pentanethylene sulfoxide and 1,4-oxathiane-4-oxide, The vibrational coupling among skeletal and S=0 deformations is discussed.     

Structure and properties of 1,4-benzenedimethanethiol films grown from solution on Au(1 1 1): An XPS and NEXAFS study

Core level photoemission and X-ray absorption at the carbon C 1s edge are applied to the study of chemisorption of 1,4-benzenedimethanethiol molecules on Au(1 1 1) and to investigate the effect of the solvent used to prepare the organic films. 1,4-Benzenedimethanethiol films were prepared in polar and non-polar solvents, i.e. ethanol, methanol and n-hexane. 1,4-Benzenedimethanethiol molecules are anchored to the substrate through a single S-Au bond; the molecules in the films tend to assume an upright orientation, the aromatic ring resulting tilted towards the direction perpendicular to the substrate plane. The films present an effective thickness corresponding to more than a single layer. Only small differences are observed among behaviours in different solvents. It is concluded that the final properties and conformation of the 1,4-benzenedimethanethiol films are largely determined by the reciprocal interactions between the molecules and with the substrate.     

H-1 NMR and Conformations of Halogenated 1,4-Dioxanes and 2,3-Dihydro-1,4-Dioxins

The conformations of halogenated 1,4-dioxanes have generally been studied by X-ray diffraction^1,2 in order to obtain values for the ring dihedral angles. The simple and widely used R value technique^3,4 requires two vicinal coupling constants, J-trans and J-cis, and is not useable when only one vicinal J value results, as in the halogenated dioxanes 1–5 and dihydrodioxins 7–9 listed in Tables 1 and 2.     

Photochemical reactions in polycrystalline 1-methyl-2,4,4,6-tetraphenyl-1,4-dihydropyridine

Kinetics of the colouring and bleaching reactions in polycrystalline 1-methyl-2,4,4,6-tetraphenyl-1,4-dihydropyridine embedded in KBr matrices were studied employing a non-isothermal technique. The results reported in the paper supplement those reported earlier, pointing to the existence of two parallel processes responsible for the photochromic activity of the material. Results of quantum-chemical calculations and spectroscopic measurements allow us to suggest possible reaction paths.     

An STM study of the localized atomic reaction of 1,2- and 1,4-dibromoxylene with Si(1 1 1)-7 × 7

Thermal reactions of 1,2- and 1,4-dibromoxylene (1,2- and 1,4-diBrXy) with Si(1 1 1)-7 × 7 were investigated by STM at room temperature under UHV conditions. Reaction led to the formation of single adsorbed Br-atoms or pairs of Br-atoms, in a ratio approx. 3:1 for both reagents. Experimental results were interpreted in terms of ‘parent-mediated’ (halogen atom accompanied by organic residue), and ‘daughter-mediated’ (no accompanying organic residue) reaction dynamics. Both mechanisms contributed to the bromination of the silicon surface in comparable amounts. For pairs of bromine atoms the Br–Br separation had a most probable value of 7.6 Å for 1,2-diBrXy, and 11.5 Å for 1,4-diBrXy. This separation was in each case greater than that in the diBrXy parent molecule by a few angstroms. For parent-mediated reaction the dynamics were revealed in detail by the STM images which gave the vectorial location of the halogen-atom products (distance and angle of the daughter atoms) relative to the prior location and alignment of the adsorbed parent molecule. Both reagents, 1,2- and 1,4-diBrXy, were found to be less reactive than the corresponding dibromobenzenes studied earlier in this laboratory [S. Dobrin et al., Surf. Sci. 561 (2004) 11], in both parent- and daughter-mediated modes.     

Covalent binding of cyclohexene, 1,3-cyclohexadiene and 1,4-cyclohexadiene on Si(1 1 1)-7 × 7

The adsorption reactions and binding configurations of cyclohexene, 1,3-cyclohexadiene and 1,4-cyclohexadiene on Si(1 1 1)-7 × 7 were studied using high-resolution electron energy loss spectroscopy (HREELS), ultraviolet photoelectron spectroscopy (UPS), X-ray photoelectron spectroscopy (XPS) and DFT calculation. The covalent attachments of these unsaturated hydrocarbons to Si(1 1 1)-7 × 7 through the formation of Si–C linkages are clearly demonstrated by the observation of the Si–C stretching mode at 450–500 cm⁻¹ in their HREELS spectra. For chemisorbed cyclohexene, the involvement of π_C=C in binding is further supported by the absence of C=C stretching modes and the disappearance of the π_C=C photoemission. The chemisorption of both 1,3-cyclohexadiene and 1,4-cyclohexadiene leads to the formation of cyclohexene-like intermediates through di-σ bonding. The existence of one π_C=C bond in their chemisorbed states is confirmed by the observation of the C=C and (sp²)C---H stretching modes and the UPS and XPS results. DFT calculations show that [4 + 2]-like cycloaddition is thermodynamically preferred for 1,3-cyclohexadiene on Si(1 1 1)-7 × 7, but a [2 + 2]-like reaction mechanism is proposed for the covalent attachment of cyclohexene and 1,4-cyclohexadiene.     

An STM study of the localized atomic reaction of 1,2- and 1,4-dibromobenzene at Si(1 1 1)-7 × 7

A comparative study is reported of the thermal reaction of 1,2- and 1,4-dibromobenzene (1,2- and 1,4-diBrPh) on Si(1 1 1)-7 × 7, investigated by STM. Some results are given for the intermediate case of 1,3-diBrPh. The STM images gave evidence of a different pattern of reaction to yield pairs of Br-Si for 1,2-, 1,3- and 1,4-diBrPh. The ratio of pairs of Br-Si to single bromination events was 1:2 for 1,2-diBrPh and 1:3 for 1,4-diBrPh. In many cases organic residue from the bromination reaction, R-Si, was evident in the STM image. The products R-Si and Br-Si were found to be bound to adjacent Si, for both 1,2- and 1,4-diBrPh. The mean Br?Br pair separation at the surface depended on the parent molecule, being 7.6 Å for 1,2-diBrPh, 10.3 Å for 1,3-diBrPh, and 11.3 Å for 1,4-diBrPh. These separations are, in each case, about 4 Å greater than the separation of the Br-atoms in the intact parent molecule, which increases systematically down the series. There was a marked decrease in the percentage of R-Si accompanying the Br-Si in going down the series, decreasing from 70% for 1,2- to 20% for 1,4-diBrPh; this was interpreted as being due to a decrease in the percentage of `benzene-mediated' reaction dynamics, in which the benzene ring was bound to the surface. At moderately increased surface temperature (45 °C) the reaction of 1,2- and also 1,4-diBrPh no longer resulted in R-Si formation, suggesting that the dynamics had altered from benzene-mediated to `bromine-mediated'.     

Calculation of frequencies of normal vibrations and interpretation of IR spectra for 2,3-dihydro-3-O-(1,4-naphthoquinon-2-yl)-2-oxo-1,4-naphthoquinone derivatives

We have used B3LYP/6-31(d) density functional theory to calculate the frequencies and modes of the normal vibrations of 2-oxo-2,3-dihydro-and 2-methoxy-1,4-naphthoquinones. Based on these calculations within an additive model, we have assigned the carbonyl bands in the IR spectra of 2,3-dihydro-3-O-(1,4-naphthoquinon-2-yl)-2-oxo-1,4-naphthoquinones (diquinones 1–4). We have carried out a direct calculation of the vibrational spectra for diquinones 1–4 using PBE and B3LYP correlation functionals. We have shown that the calculation of the vibrational spectra of the diquinones based on an additive model on the whole is quite consistent with the results of direct calculations and the experimental spectra. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 6, pp. 713–720, November–December, 2006.     

Photoelectron spectra of 1,4-dithiin and related compounds

The photoelectron (He(I)) spectra of 1,4-dithiin (1), 1,4-thiaselenin (2), 1,4-thiatellurin (3) and 4H-thiopyran (4) were assigned by comparison with published spectra of similar compounds and with the help of ab initio and semi-empirical calculations. The proposed orbital sequences for the outermost orbitals are π₄, π₃, π₂, σ for 1, 2 and 3, and π₄, π₂, σ, π₃ for 4. π₄ and π₃ correspond to the symmetric and antisymmetric combinations, respectively, of the heteroatom lone pairs, while π₂ is the antisymmetric combination of the π_eth orbitals.     

Effect of Excited-state Substituent Constant on the UV Spectra of 1,4-disubstituted Benzenes

构建激发态取代基参数与1,4-二取代苯的紫外吸收波数之间的模型,成功地关联80个1,4-二取代苯的紫外吸收波数,其方程的相关系数为0.9805,标准偏差仅为672.27 cm^-1．结果表明激发态取代基参数适用于1,4-二取代苯紫外吸收能量的研究．同时提供了研究芳香化合物的紫外吸收光谱的新方法,并有利于深入理解多取代共轭化合物的激发态物理化学性质中的取代基效应     

Conformational analysis of 2,3-dihydro-3-O-(1,4-naphthoquinon-2-yl)-2-oxo-1,4-naphthoquinone derivatives by the density functional method and IR spectroscopy

We have used the PBE/3z, B3LYP/6-31G, B3LYP/6-31G(d), and B3LYP/6-311G(d) methods to study the conformational mobility of 2,3-dihydro-3-O-(1,4-naphthoquinon-2-yl)-2-oxo-1,4-naphthoquinones (1–4). We have shown that more than 99% of these compounds exist as the major tautomeric form, while differences in the structure of the Q_2H (2,3-dihydro-2-oxo-1,4-naphthoquinones) and Q_1,4 (1,4-naphthoquinon-2-yl) moieties lead to qualitative differences in the internal rotation potentials of the ethyl substituents V(θ_Et−1) and V(θ_Et−2), and consequently each of compounds 1−4 exists as six different rotameric forms. For diquinone 3, we have calculated the dependences of the frequencies (ν) and intensities (A) of the normal vibrations on the torsional angles θ_Et−1 and θ_Et−2, and also on the changes in the geometry of the ether bond. We have found that the values of ν and A for the bands in the carbonyl region of the IR spectrum change little on going from one rotameric form to another, and also for the in-plane bends of the ether bond, and change considerably for the out-of-plane bends of the ether bond. However, for T ≤ 300 K, there is no qualitative change in the overall contour, and it can be interpreted based on a simple additive model. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 5, pp. 573–581, September–October, 2006.     

Linear Dichroism of 1,4-Benzodiazepines

Linear dichroism and absorption spectra were measured for some 1,4-benzodiazepines dissolved and partially oriented in a polymer matrix. The results are discussed in terms of polarizations of the transitions in the two noninteracting benzene nuclei.     

1,4-萘醌的太赫兹,远红外及低频拉曼光谱研究

本文对1,4-萘醌进行了太赫兹时域光谱,远红外吸收光谱及低频拉曼散射谱的测试研究。1,4-萘醌的太赫兹吸收光谱与远红外谱仪测得的光谱取得了在1.75 THz(58.3 cm-1)/1.63 THz(54.3 cm-1)等处吸收峰位基本相同、两者相互佐证和补充的结果。将太赫兹和远红外吸收谱与低频拉曼散射谱进行比较,表明两种选择机制不同的光谱在1.04,1.72和4.59 THz等处的峰位基本重合,结合群论的不可约表示理论分析,表明该样品在低频波段具有拉曼活性和红外活性的振动属性(A1、B1或B2)。采用Gaussi-an03软件的密度泛函理论B3LYP函数和6-311基组模拟单分子红外与拉曼光谱,结合实验分析,对部分分子基团或原子振转模式给与了指认。     

Structure and Properties of a cis-1,4-Polybutadiene/Organic Montmorillonite Nanocomposite Prepared via In Situ Polymerization

Cis-1,4-polybutadiene (cis-1,4-PB) is one of the most important synthetic rubbers, having superior performances such as wear resistance, cold resistance and high elasticity. However, its mechanical properties, including low tensile strength, tear resistance and thermal stability, limit its application in comparison to natural rubber and butadiene-styrene rubber that have excellent overall performances. Thus, the reinforcing of cis-1,4-PB is a necessity. The dispersion of clay in rubbers on the nanoscale can improve the mechanical, gas permeability and thermal properties of the resulting composites. In this paper, organic montmorillonite (OMMT) clay was dispersed into the cis-1,4-PB matrix via an in-situ polymerization method and the chemical structure, phase morphology, mechanical properties and thermal stability of the composite were investigated. The properties of the composite were analyzed by such techniques as X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM) and thermal gravimetric analysis (TGA). In the in-situ polymerization, a Ni-based catalyst system with the presence of OMMT showed high efficiency and 1,4-selectivity for the polymerization of butadiene. The OMMT could be dispersed in the polymeric matrix on the nanoscale during the polymerization. The interfusion of OMMT had little influence on the thermal stability and the chemical micro-structure of the cis-1,4-PB when the content of cis-1,4 units was more than 95%. The loss tangent of the composite was higher than that of cis-1,4-PB from ?110 to ?55°C, the temperature range examined, and the mechanical properties of the cis-1,4-PB/OMMT nanocomposite (NC) were improved upon the addition of OMMT.     

Catalytic dehydrogenation and thermal chemistry of cyclohexene and 1-methyl-1,4-cyclohexadiene on Si(111)7 × 7

Recently, we reported a thermal desorption study on the evolution of an intense mass 78 profile for the room-temperature exposure of cyclohexene to Si(111)7 × 7 surface, which was believed to give rise to the formation of benzene by a surface dehydrogenation reaction. Because mass 78 was also found to be the base ion in the gas-phase cracking patterns of both 1,3- and 1,4-cyclohexadiene, the dehydrogenation of cyclohexene on clean, sputtered and oxidized Si(111)7 × 7 surfaces has been re-examined in order to determine the origin of the intense mass 78 desorption profile; i.e. whether it was in fact due to the evolution of benzene or cyclohexadiene, or both. Moreover, a similar dehydrogenation reaction giving rise to toluene desorption between 350 and 600 K has been observed for the room-temperature exposure of 1-methyl-1,4-cyclohexadiene to clean and sputtered Si(111)7 × 7 surfaces. The effects of methyl substitution on the reactivity of these cyclic olefins towards Si(111)7 × 7 can be inferred from these studies. Furthermore, the catalytic activity of Si(111)7 × 7 was found to be enhanced significantly by extending the thermal desorption cycles to a higher temperature of 925 K. The dehydrogenation of these olefins on Si(111)7 × 7 also gave rise to a unique 7 × 1 low energy electron diffraction pattern. Possible factors that may play a role in any proposed model for the dehydrogenation reaction are discussed. Finally, evidence of other surface reactions including cyclohexene hydrogénation to cyclohexane will also be presented.     

3,5-二乙酰基-1,4-二氢吡啶热致变色性质的研究

研究了3,5-二乙酰基-1,4-二氢吡啶的热致变色过程中吸收光谱的变化,考察了溶剂、酸碱性、加热时间和温度等因素对热致变色现象的影响,并简要讨论了可能的变色机理。     

X-ray structure analysis of trans-1,4-polybutadiene

The crystal structure of trans-1,4-polybutadiene has been reported by Natta et al. to be pseudo-hexagonal below its solid-phase transition temperature. In the present X-ray structure analysis, it is revealed that the crystal belongs to the monoclinic system with the space group P2¹/a. The unit cell, with the lattice constants a = 8.63 Å, b = 9.11 Å, c = 4.83 Å, and β = 114°, includes four molecular segments.     

Rh(I)/Sc(OTf)3-co-catalyzed Michael addition of ammonium ylide to (E)-1,4-enediones: synthesis of functionalized 1,4-diketones

Molecular Diversity - A Rh(I)/Sc(III) co-catalyzed synthesis of highly valuable functionalized 1,4-diketone derivatives in good yields and with an excellent diastereoselectivity. The established...     

Ultrasound-assisted photochemical oxidation of unsymmetrically substituted 1,4-dihydropyridines

The combination of ultrasound and photochemistry has been used for the oxidation of unsymmetrical 1,4-dihydropyridines to the pyridine derivatives. An ultrasonic probe of 24 kHz frequency and a Hg-lamp of 100 W have been used for this study. The effect of parameters such as ultrasonic intensity, the presence of oxygen and argon atmospheres and also the separate usage of one of these irradiation sources have been studied. Whereas sonication of these compounds alone did not result in the oxidation of them, the use of ultrasound increases the rate of photo-oxidation. The presence of oxygen decreases or increases the rate of reaction, depending on the type of excited state of 1,4-dihydropyridines involved in the reaction.     

Effect of TiO2 powder addition on sonochemical destruction of 1,4-dioxane in aqueous systems

Effects of TiO(2) powder addition on sonochemical destruction of 1,4-dioxane in water were investigated through comparison of a SiO(2) powder that had similar specific surface area. Results show that addition of TiO(2) is more effective for decomposition of 1,4-dioxane in water than addition of SiO(2). The contribution of photocatalytic destruction through sonoluminescence is not a dominant mechanism for acceleration of sonochemical reactions by adding TiO(2). Sonication of TiO(2)-added water generated thermally excited holes in this case. Moreover, intrinsic oxygen vacancies in TiO(2) surface play an important role in achieving high decomposition efficiency by producing cavitation. The addition of reduced TiO(2) powder increases both the ultrasonication energy that is consumed in water and the destruction efficiency of 1,4-dioxane.