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1.
Difference X‐ray photoelectron spectroscopy (D‐XPS) revealed the surface oxidation process of a diamond‐like carbon (DLC) film. Evaluation of surface functional groups on DLC solely by the C 1s spectrum is difficult because the spectrum is broad and has a secondary asymmetric lineshape. D‐XPS clarified the subtle but critical changes at the DLC surface caused by wet oxidation. The hydroxyl (C―OH) group was dominant at the oxidized surface. Further oxidized carbonyl (C?O) and carboxyl (including carboxylate) (COO) groups were also obtained; however, the oxidation of C?O to COO was suppressed to some extent because the reaction required C―C bond cleavage. Wet oxidation cleaved the aliphatic hydrogenated and non‐hydrogenated sp2 carbon bonds (C―H sp2 and C―C sp2) to create a pair of C―OH and hydrogenated sp3 carbon (C―H sp3) bonds. The reaction yield for C―H sp2 was superior at the surface, suggesting that the DLC film was hydrogen rich at the surface. Oxidation of aromatic sp2 rings or polycyclic aromatic hydrocarbons such as nanographite to phenols did not occur because of their resonance stabilization with electron delocalization. Non‐hydrogenated sp3 carbon (C―C sp3) bonds were not affected by oxidation, suggesting that these bonds are chemically inert. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

2.
In the past 5 years, transition-metal-mediated trifluoromethylation for the construction of various CF3-containing building blocks has been the focus of recent research in both industrial and academic communities. Progresses in the construction of C(sp2)–CF3 bonds and C(sp)–CF3 have been well reviewed. This Letter will focus on the cases of transition-metal-mediated C(sp3)–CF3 bond formation, which involves the trifluoromethylation of sp3-hybridized C–X bonds, alkyl organometallic reagents, sp3-hybridized C–H bonds, and alkene derivatives.  相似文献   

3.
Amorphous carbon (or diamond-like carbon, DLC) films have shown a number of important properties usable for a wide range of applications for very thin coatings with low friction and good wear resistance. DLC films alloyed with (semi-)metals show some improved properties and can be deposited by various methods. Among those, the widely used magnetron sputtering of carbon targets is known to increase the number of defects in the films. Therefore, in this paper an alternative approach of depositing silicon-carbide-containing polymeric hydrogenated DLC films using unbalanced magnetron sputtering was investigated. The influence of the C2H2 precursor concentration in the deposition chamber on the chemical and structural properties of the deposited films was investigated by Raman spectroscopy, X-ray photoelectron spectroscopy and elastic recoil detection analysis. Roughness, mechanical properties and scratch response of the films were evaluated with the help of atomic force microscopy and nanoindentation. The Raman spectra revealed a strong correlation of the film structure with the C2H2 concentration during deposition. A higher C2H2 flow rate results in an increase in SiC content and decrease in hydrogen content in the film. This in turn increases hardness and elastic modulus and decreases the ratio H/E and H3/E2. The highest scratch resistance is exhibited by the film with the highest hardness, and the film having the highest overall sp3 bond content shows the highest elastic recovery during scratching.  相似文献   

4.
A non-ionic polymer (poly(vinyl alcohol) (PVA)) has been incorporated into the inorganic layers of calcium silicate hydrate (C–S–H) during precipitation of quasicrystalline C–S–H from aqueous solution. C–S–H and a C–S–H-polymer nanocomposite (C–S–HPN) material were synthesized and characterized by X-ray fluorescence (XRF), energy dispersive spectroscopy (EDS), 29Si magic angle spinning nuclear magnetic resonance (29Si MAS NMR) and 13C cross-polarization nuclear magnetic resonance (13C CP NMR) spectroscopy, atomic force microscopy (AFM), thermal conductivity, thermogravimetric analysis (TG) and differential thermal analysis (DTA). Thermal conductivity of PVA, C–S–H and C–S–HPN material was studied in the temperature range 25–50°C. C–S–HPN materials exhibited the highest thermal conductivity at 25 and 50°C. The thermal conductivity increases from 25 to 50°C are 7.03, 17.46 and 14.85% for PVA, C–S–H and C–S–HPN material, respectively. Three significant decomposition temperature ranges were observed on the TG curve of C–S–HPN material.  相似文献   

5.
Summary.  Malonic ester derivatives of ethyl and methyl 3,5-dimethyl-4-(1′-iodoneopentyl)-1H-pyrrole-2-carboxylate exhibit restricted rotation about the pyrrole C(4)–C(1′) bond due to the bulky 1′-tert-butyl and malonic ester groups and the ortho effect at C(4) of the sterically crowded 3,5-dimethylpyrrole. The malonates belong to a rare class of atropisomers with restricted rotation about an sp3–sp2 C–C bond, and they undergo diastereomeric separation by TLC and crystallization: the diastereomers are stable in solution at room temperature. A crystal of one of the diastereomers, suitable for X-ray crystallography, gave the relative configuration of the chiral axis and stereogenic center at C(1′). Dynamic NMR studies of the purified diastereomers provide kinetic and thermodynamic parameters associated with the atropisomerism: ΔG  = 132–134 kJ/mol (∼32 kcal/mol) at 383 K in C2D2Cl4 solvent. Corresponding author. E-mail: lightner@scs.unr.edu Received July 1, 2002; accepted July 8, 2002  相似文献   

6.
The existence of a short C–H ⋯ π (alkyl–alkyne) interaction in the structure of a strained and relatively rigid tolanophane is expected to hinder the rotation about the C–C sp3 single bond. Variable-temperature NMR experiments (performed in three solvents, CDCl3, THF-d8, and acetone-d6) and ab initio density functional calculations were carried out to investigate its dynamic nature. An energy barrier of 48.6 kJ/mol is determined at coalescence (210 K) with acetone-d6 which is in good agreement with calculation result (54 kJ/mol). Correspondence: Hossein Reza Darabi, Chemistry and Chemical Engineering Research Center of Iran, Pajoohesh Blvd., km 17, Karaj Hwy, 14968-13151 Tehran, Iran.  相似文献   

7.
Plasma‐enhanced chemical vapor deposition was employed to fabricate hydrogenated amorphous carbon (a‐C:H) films and fluorine‐doped hydrogenated amorphous (a‐C:H:F) carbon films. For comparison purpose, the a‐C:H films were treated with CF4 plasma. The bonding structure and tribological behavior of the films were investigated. The results indicate that the F presented mainly in the forms of C–F3, C–F and C–F2 groups in both the a‐C:H:F film and the surface CF4 plasma processed hydrogenated amorphous carbon (F‐P‐a‐C:H) films. Moreover, the a‐C:H:F films, because of the transformation of sp3 to sp2, possess a lower friction coefficient than that of the F‐P‐a‐C:H films. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

8.
Vinyltri(phenylethynyl)silane ((ph–C≡C)3–Si–C=CH2; VTPES) and phenyltri(phenylethynyl)silane ((ph–C≡C)3–Si–ph; PTPES) were synthesized by Grignard reaction. Their molecular structures were characterized by means of 1H NMR, 13C NMR, 29Si NMR, and FT-IR spectroscopy. Their nonisothermal thermal curing processes were characterized by DSC, and the corresponding kinetic data, for example activation energy (E), pre-exponential factor (A), and the order of the reaction (n), were obtained by the Kissinger method. The results showed that the melting points of VTPES and PTPES were 84 and 116 °C, respectively. Their curing reaction rates were consistent with first-order kinetic equations. VTPES monomer had a lower activation energy and curing temperature as a result of coordination between reactive groups.  相似文献   

9.
The search for novel, atom-economic methods for the formation of C–C bonds is of crucial importance in synthetic chemistry. Especially attractive are reactions where C–C bonds are formed through C–H activation, but the coupling of unactivated, alkane-type Csp3–H bonds remains an unsolved challenge. Here, we report iridium-mediated intramolecular coupling reactions involving up to four unactivated Csp3–H bonds to give carbon–carbon double bonds under the extrusion of dihydrogen. The reaction described herein is completely reversible and the direction can be controlled by altering the reaction conditions. With a hydrogen acceptor present a C–C double bond is formed, while reacting under dihydrogen pressure leads to the reverse process, with some of the steps representing net Csp3–Csp3 bond cleavage. Mechanistic investigations revealed a conceptually-novel overall reactivity pattern where insertion or deinsertion of an Ir carbene moiety, formed via double C–H activation, into an Ir–C bond is responsible for the key C–C bond formation and cleavage steps.  相似文献   

10.
On the Nature of Carbonyl Groups in Cellulosic Pulps   总被引:2,自引:0,他引:2  
Apart from the reducing end groups, most celluloses contain small amounts of carbonyl groups in the mol/g range, which are introduced into the material by a variety of preparation, processing and purification steps. By a combination of carbonyl-selective fluorescence labeling (CCOA method) and UV resonance Raman spectroscopy it was demonstrated that carbonyls in celluloses are not only present as a C=O structure with an sp2-hybridized carbon, but also to a significant extent in sp3-hybridized form as hydrates or hemiacetals.  相似文献   

11.
Two new crystalline guaianolides,viz., rhaposerine and rhaserolide, were isolated from an ethanolic extract of the above-ground part of the plantRhaponticum serratuloides by column chromatography along with sesquiterpene lactones,viz., centaurepensin and acroptilin, which have been found in other plants. The chemical structures of the title lactones were established by1H and13C NMR spectroscopy and 2D1H−1H (COSY) and13C−1H (COSY and COLOC) NMR spectroscopy. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 2010–2014, October, 1999.  相似文献   

12.
The hydrogenated amorphous carbon nitride (a‐CNx:H) thin films were synthesized on the SS‐304 substrates using a dense plasma focus device. The a‐CNx:H thin films were synthesized using CH4/N2 admixture gas and 20 focus deposition shots on substrates placed at different distances from the anode top. X‐ray photoelectron spectroscopy and Raman analysis confirmed different C–N bonding in the a‐CNx:H thin films. A decrease in the N/C ratio as well as the sp3/sp2 ratio with an increase in the substrate distance has been observed. The higher amount of C–N formation for the film synthesized at 10 cm is observed which decreases with increasing distance. The X‐ray photoelectron spectroscopy and Raman analysis affirmed the C ≡ N presence in all the thin films synthesized at different distances. The morphology of the synthesized a‐CNx:H thin films showed nanoparticles and nanoparticle clusters formation at the surface. The hardness results showed comparatively lower hardness of the a‐CNx:H thin films due to the presence of C ≡ N. The C–N formation with lower amount of C ≡ N and a higher N/C ratio as well as a higher sp3/sp2 ratio for the films synthesized at 10 cm show reasonably higher hardness. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

13.
The conformational composition of gaseous MTMNB and the molecular structures of the rotational forms have been studied by electron diffraction at 130C aided by results from ab initio and density functional theory calculations. The conformational potential energy surface has been investigated by using the B3LYP/6-31G(d,p) method. As a result, six minimum-energy conformers have been identified. Geometries of all conformers were optimized using MP2/6-31G(d,p), B3LYP/6-31G(d,p), and B3LYP/cc-pVTZ methods. These calculations resulted in accurate geometries, relative energies, and harmonic vibrational frequencies for all conformers. The B3LYP/cc-pVTZ energies were then used to calculate the Boltzmann distribution of conformers. The best fit of the electron diffraction data to calculated values was obtained for the six conformer model, in agreement with the theoretical predictions. Average parameter values (ra in angstroms, angle α in degrees, and estimated total errors given in parentheses) weighted for the mixture of six conformers are r(C–C) = 1.507(5), r(C–C)ring, av = 1.397(3), r(C–S)av = 1.814(4), r(C–N) = 1.495(4), r(N–O)av = 1.223(3), ∠(C–C–C)ring = 116.0–122.5, ∠ C6–C4–C7 = 118.2(4), ∠ C–C–S = 113.6(6), ∠ C–S–C = 98.5(12), ∠ N–C–C4 = 121.9(3), ∠(O–N–C)av = 116.8(3), ∠ O–N–O = 127.0(4). Torsional angles could not be refined. Theoretical B3LYP/cc-pVTZ torsional angles for the rotation about C–N bond, φCN, were found to be 30.5–36.5 for different conformers. As to internal rotation about C–C and C–S bonds, values of φCC = 68–118 and φCS = 66–71 were obtained for the three most stable conformers with gauche orientation with respect to these bonds. Some conclusions of this work were presented in a short communication in Russ. J. Phys. Chem. 2005, 79, 1701.  相似文献   

14.
 Malonic ester derivatives of ethyl and methyl 3,5-dimethyl-4-(1′-iodoneopentyl)-1H-pyrrole-2-carboxylate exhibit restricted rotation about the pyrrole C(4)–C(1′) bond due to the bulky 1′-tert-butyl and malonic ester groups and the ortho effect at C(4) of the sterically crowded 3,5-dimethylpyrrole. The malonates belong to a rare class of atropisomers with restricted rotation about an sp3–sp2 C–C bond, and they undergo diastereomeric separation by TLC and crystallization: the diastereomers are stable in solution at room temperature. A crystal of one of the diastereomers, suitable for X-ray crystallography, gave the relative configuration of the chiral axis and stereogenic center at C(1′). Dynamic NMR studies of the purified diastereomers provide kinetic and thermodynamic parameters associated with the atropisomerism: ΔG  = 132–134 kJ/mol (∼32 kcal/mol) at 383 K in C2D2Cl4 solvent.  相似文献   

15.
Silver assisted de-bromination gives [Au2(dppm/dppe/dppa) (OTf)2], which on reaction with 4,4′-bpy and gold(I) phosphines in CH2Cl2 medium, by the self assembly technique, leads to [(PPh3)Au(4,4′-bpy)Au(PPh3)], (1a–1d,2), [{Au2(dppm/dppe/dppa)}{(4,4-bpy)Au(PPh3)}2](NO3)4, (3), [{Au4(dppm/dppe/dppa)2(4,4-bpy)2}](OTf)4, (4), [{(PPh3)AuI(4,4′-bpy)}2AuIII(C6F5/Mes)](NO3)3, (5) [dppm/dppe/dppa =diphenyl phosphino-methane(a), –ethane(b), ammine(c), C6F5/Mes pentafluorophenyl/mesitylene]. The maximum molecular peak of the corresponding molecule is observed in the ESI mass spectrum. Ir spectra of the complexes show –C=C–, –C=N–, as well as phosphine, mesitylene and pentafluorophenyl stretching. The 1H-NMR spectra as well as 31P(1H)-NMR suggest solution stereochemistry, proton movement and phosphorus proton interaction. Considering all the moities there are a lot of carbon atoms in the molecule reflected by the 13C(H)-NMR spectrum. In the 1H–1H COSY spectrum of the present complexes and contour peaks in the 1H–13C-HMQC spectrum, assign the solution structure and stereoretentive transformation in each step.  相似文献   

16.
The structural and electronic characteristics of thin diamond-like nanocrystallites (with cross-sectional areas 5 < S < 280 Å2) were investigated by the electron density functional tight binding (DFTB) method. A new type of extended “hybrid” (sp3 + sp2) nanostructures, in the form of monolithic diamond-like sp3 crystallites encapsulated in a graphite-like sp2 shell, was discovered. __________ Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 42, No. 4, pp. 199–203, July–August, 2006.  相似文献   

17.
Allenes (>C=C=C<) are classified as cumulated dienes with a linear structure and an sp-hybridized central carbon atom. We have synthesized and isolated a stable 2-germapropadiene with bulky silyl substituents. The 2-germapropadiene allene moiety adopts a linear structure both in the solid state and in solution. An X-ray diffraction electron-density-distribution (EDD) analysis of this 2-germapropadiene confirmed the linear C=Ge=C geometry with a formally sp-hybridized germanium atom that bears two orthogonal C=Ge π-bonds. Based on detailed structural and computational studies, we concluded that the linear geometry of the isolated 2-germapropadiene most likely arises from the negative hyperconjugation of the silyl substituents at the terminal carbon atoms. The 2-germapropadiene reacts rapidly with nucleophiles, indicating that the linearly oriented germanium atom is highly electrophilic.  相似文献   

18.
The interaction between the Co sulfide coating formed on a glassy carbon electrode and Cu(I)-ammonia complexes solution was investigated by cyclic voltammetry in 0.1 M KClO4, 0.1 M NaOH and 0.05 M H2SO4 solutions. It was determined that, after treating the cobalt sulfide coating formed by two deposition cycles with Cu(I)-ammonia complexes (0.4 M, pH 8.8–9.0, τ=180 s, T=25±1°C), an exchange occurs between the coating components and Cu(I). Copper(I) substitutes 75% of the Co(III) compounds present in the coating (~1.81×10–7 mol cm–2) because of Cu2O (1.36×10–7 mol cm–2) formation. The rest of the Co(II) and Co(III) sulfide compounds are also replaced by copper with formation of Cu2– x S with a stoichiometric coefficient close to 2 (~1.9). After modifying the cobalt sulfide coatings with Cu(I) ions, the total amount of metal (Co+Cu) increases, owing to the sorption of Cu(I) compounds. In addition, the number of deposition cycles decreases from 3 to 1.5 [1 cycle involves cobalt sulfide layer formation and 0.5 cycle is attributed to modifying by Cu(I) ions]. The coatings modified in the above-mentioned manner may be successfully used for plastic electrochemical metallization as Cu2– x S coatings formed by three deposition cycles. Electronic Publication  相似文献   

19.
A systematic density functional theory investigation on C2Au n + (n = 1,3,5) and C2Au n (n = 2,4,6) indicates that gold atoms serve as terminals (–Au) in the chain-like Cs C2Au+ (C=C–Au+) and D∞h C2Au2 (Au–C≡C–Au) and as bridges (–Au–) in the side-on coordinated C2v C2Au3 + ([Au–C≡C–Au]Au+) and Cs C2HAu2 +([H–C≡C–Au]Au+). However, when the number of gold atoms reaches four, they form stable gold triangles (–Au3) in the head-on coordinated C2v C2Au4 (Au–C≡C–Au3) and the side-on coordinated C2v C2Au5 + ([Au–C≡C–Au]Au3 +). Similar –Au3 triangular units exist in the head-on coordinated C2v C2HAu3 (H–C≡C–Au3) and D2d C2Au6 (Au3–C≡C–Au3). The existence of stable –Au3 triangular units in small dicarbon aurides is significant and intriguing. The high stability of Au3 triangles originates from the fact that an equilateral D3h Au3 + cation possesses a completely delocalized three-center-two-electron (3c–2e) σ bond and therefore is σ-aromatic in nature. The extension from H/Au analogy to H/Au3 analogy established in this work may have important implications in designing new gold-containing catalysts and nano-materials.  相似文献   

20.
Olivine LiFePO4/C cathode materials for lithium ion batteries were synthesized using monodisperse polystyrene (PS) nano-spheres and other carbon sources. The structure, morphology, and electrochemical performance of LiFePO4/C were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), galvanostatic charge–discharge tests, electrochemical impedance spectroscopy (EIS) measurements, and Raman spectroscopy measurements. The results demonstrated that LiFePO4/C materials have an ordered olivine-type structure with small particle sizes. Electrochemical analyses showed that the LiFePO4/C cathode material synthesized from 7 wt.% PS nano-spheres delivers an initial discharge capacity of 167 mAh g-1 (very close to the theoretical capacity of 170 mAh g-1) at 0.1 C rate cycled between 2.5 and 4.1 V with excellent capacity retention after 50 cycles. According to Raman spectroscopy and EIS analysis, this composite had a lower I D/I G, sp 3/sp 2 peak ratio, charge transfer resistance, and a higher exchange current density, indicating an improved electrochemical performance, due to the increased proportion of graphite-like carbon formed during pyrolysis of PS nano-spheres, containing functionalized aromatic groups.  相似文献   

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