Cyclohexane Molecules Research Articles

Time-Resolved Sum-Frequency Generation Spectroscopy of Cyclohexane Adsorbed on Ni(111) under Ultrashort NIR Laser Pulse Irradiation

The adsorption of cyclohexane on Ni(111) was studied by infrared-visible sum-frequency generation (SFG) spectroscopy with and without near-infrared (NIR) pump pulse irradiation. Two adsorption states of cyclohexane were found in the monolayer region, a low-coverage state showing SFG peaks at 2740, 2815, and 2865 cm(-1), and a high-coverage state showing peaks at 2740, 2815, and 2905 cm(-1). Both states coexisted on the saturated Ni(111) surface. The broad peak at 2740 cm(-1) was due to the softened CH stretching mode of the axial CH groups of cyclohexane that point toward the Ni(111) surface. The peaks at 2815 and 2865 (or 2905) cm(-1) were due to the symmetric and asymmetric stretching modes of CH(2) groups, respectively, that were free from the surface. Irradiation with NIR pulses caused a temporary jump in temperature at the Ni(111) surface and enhanced the intensity of the 2905 cm(-1) peak, but weakened the other peaks. This indicates that the temperature jump excited the cyclohexane molecules from the low-coverage state to the high-coverage state. The dynamics of the structural change observed in the adsorbed cyclohexane on NIR irradiation is discussed.

Total cross-section measurements for positrons and electrons colliding with alkane molecules: Normal hexane and cyclohexane

Total cross sections (TCSs) for $0.2--1000\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ positrons and $0.4--1000\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ electrons colliding with normal hexane and cyclohexane molecules are reported. For positron scattering, low-lying peaks at $0.8\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ for normal hexane and $1.6\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ for cyclohexane are observed. For both molecules, positron TCSs are larger than electron TCSs below $2.8\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$; for electron scattering, the main resonance peak in the TCS curve is at $7.5\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$, followed by a shoulder at about $22\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$. TCSs for normal hexane are larger than those for cyclohexane for both positrons and electrons over all the energy range. Striking similarities, more pronounced for electron impact, have been observed between $c$-hexane and benzene TCSs and are attributed to the similarity in molecular structure between these two molecules, whereby each has a hexagonal ring based on the six C atoms.

A New Inclusion Compound between 2,4,5,7,9,10-hexachloro-1,3,6,8-tetrakis (4-methoxyphenylthio)pyrene Host and Cyclohexane Guest Stabilized by C–H···π and C–H···Cl Interaction

Crystal structure analysis shows the 2,4,5,7,9,10-hexachloro-1,3,6,8-tetrakis-(4-methoxyphenylthio) pyrene host and its cyclohexane guest in the Pnma crystal lattice. The crystal data and refinement parameter for the title compound are: a = 15.864(3), b = 30.455(6), c = 9.231(5) A, V = 4459.2 (14) A3. For Z = 4 and M w = 1045.76, the calculate density Dcal = 1.558 g/cm3. The C–H···π interaction and C–H Cl interaction stabilized the inclusion of cyclohexane molecules. The S···Cl weak interaction assembled the host molecules into a two-dimensional layer structure, and a three-dimensional structure was obtained by connecting the layers with C–H···O hydrogen bonding.

The Structure of a Trimolecular Liquid: tert-Butyl Alcohol:Cyclohexene:Water

The structure of the trimolecular liquid mixture of 2:6:1 cyclohexene, tert-butyl alcohol, and water has been investigated using hydrogen/deuterium substitution neutron scattering techniques, and a three-dimensional structural model refined to be consistent with the experimental data has been built using the technique of Empirical Potential Structure Refinement. The model shows a well-mixed solution of the three molecular components where the competing interactions between the nonpolar cyclohexene and polar water molecules are balanced in the solution leading to largely pure-alcohol-like interactions between the tert-butyl alcohol molecules. Cyclohexene molecules favor direct solvation by alcohol methyl groups while water molecules are accommodated, dispersed throughout the solution, via hydrogen bonding interactions with the alcohol molecule hydroxyl groups. Rare occurrences of direct cyclohexene-water interactions are of the classic hydrophobic hydration type and no evidence is found for microscopic heterogeneity in the trimolecular mixture in contrast to the general findings for binary alcohol-water solutions.

Gelation Process of Toluene-Based bis-Urea in Cyclohexane Studied with Magnetic Resonance Imaging

Magnetic resonance imaging was used for studies of the gelation and swelling processes of toluene-based bis-urea prepared in a form of cylindrical tablet and immersed in cyclohexane. The processes were investigated with the use of Bruker AVANCE (300 MHz) spectrometer equipped with a micro imaging probe head. The images were taken for cyclohexane protons within the bis-urea gel formed around the sample dry core at different intervals of the immersion. The mobility of the solvent molecules was estimated from the spatially resolved distribution of the spin–spin relaxation time T2 and the spin densities ρ, calculated on the basis of the images obtained. It was shown that the time-evolution of the thickness of the gel layer can be well described by the power equation with an exponent equal to 0.47 (±0.04), indicating the Fickian nature of the diffusion of cyclohexane molecules.

DFT—Quantum chemical study of the HZSM-5-cyclohexene interaction pathways

A theoretical analysis of the interaction between cyclohexene and a HZSM-5 zeolite model system is presented. Two different models were used to represent this catalyst: a ring structure model consisting of 10 TO 4 tetrahedral sites (where T = Si, Al) and a smaller model containing 3 TO 4 tetrahedral sites. Two different reaction pathways were studied: the hydrogen exchange between the HZSM-5 cluster model and the cyclohexene molecule, and the proton addition to double bond of the cyclohexene. The alkoxy species can be stabilized/destabilized depending of the arrangement restriction between the olefin and the local geometry of the active site. When cyclohexene molecule interacts with the 3T model the reaction involves an alkoxy species formation. Due to the allowed relaxation in the ring framework around the active site, the local arrangement restriction of the alkoxy species and therefore the covalent alkoxy bond is too weak giving rise to a more ionic intermediate species (carbenium ion-like), which is characterized as a minimum in the PES. By using the non-interacting system, as a reference, and based on the calculated changes in the total energy of the different complexes, one is able to determine that both carbenium ion-like and alkoxy species are destabilized with respect to physisorbed complexes.

Adsorption and reaction of cyclohexene and 1-hexene on nascent gold surface formed by friction

Adsorption and reaction of cyclohexene, 1-hexene and benzene on nascent gold surface formed by friction were investigated using an adsorption test apparatus in high vacuum at room temperature. Chemisorption of cyclohexene, 1-hexene and benzene was observed during the sliding processes by a quadrupole mass spectrometer. It is found that nascent gold surface has catalytic activity for hydrogenation of cyclohexene and 1-hexene, and for dehydrogenation of the olefins and benzene. The adsorbed cyclohexene and 1-hexene molecules were hydrogenated on the surface to form cyclohexane and hexane, respectively. As dehydrogenation products, hydrogen from all the sample gases, and benzene from cyclohexene desorbed. Adsorption rate of the olefins was higher than that of benzene, and hydrogenation activity of 1-hexene is higher than that of cyclohexene. However, on nascent Pd–Ag alloy surface, the desorption of hydrogenation products was not detected, although adsorption of the sample gases and desorption of the dehydrogenation products were also observed.

A Study of Pore Blockage in Silicalite Zeolite Using Free Energy Perturbation Calculations

Binary systems consisting of large coadsorbed molecules (n-hexane, cyclohexane, and benzene) with smaller penetrant molecules (methane) were simulated to investigate the mechanisms of pore blockage in the zeolite silicalite. Benzene and cyclohexane trap the methane molecules in the zeolite channels on the time scales of molecular dynamics simulations. Minimum energy paths for methane diffusion past the blocking molecules were determined, and free energy perturbation calculations were carried out along the paths to get the rate constants of methane hopping past coadsorbed benzene and cyclohexane molecules, which adsorb in the channel intersections. Three principal diffusion pathways were found in both the methane/benzene and methane/cyclohexane systems. Minima which were connected by low-energy pathways were grouped together into macrostates. Using the calculated hopping rates between macrostates, kinetic Monte Carlo was then used to obtain the diffusivity of methane with a coadsorbate benzene loading such that all channel intersections are filled by benzene - conditions where molecular dynamics simulations fail. Passage of methane across cyclohexane molecules involved pushing the cyclohexane molecules into the channels from their preferred channel intersection positions.

C141 エタノール/シクロヘキサン混合溶液構造の溶液モル比率依存性およびエタノール拡散係数変化の分子論的解釈(OS-11 ナノスケール伝熱IV)

Until now, huge amount of theoretical study aiming a molecular interpretation of transport properties of a binary liquid has been performed. Whereas the transport properties of a simple binary liquid such as a Lennard-Jones binary liquid can be explained in a molecular level, those of an associated binary fluid such as surfactant/oil mixture and water solution cannot be explained in a general way. This is because the anisotropic hydrogen bonding between their hydrophilic groups results in the formation of molecular clusters having a characteristic shape, and therefore makes it difficult to establish a general model of such a complex liquid. This paper reports the results of a series of the molecular dynamics (MD) studies where the molar fraction of ethanol in ethanol/cyclohexane binary liquid was chosen in a whole range with an increment of 0.1. The OPLS-UA and 6-sited Lennard-Jones were used as a potential model of ethanol and cyclohexane molecules. The NVT (T=298.15K) ensemble was applied with the cubic periodic unit cell. The detection of the hydrogen bonding between the hydroxyl group of ethanol molecule makes it possible to expose the mesoscopic structure of ethanol clusters. On the other hand, a self-diffusion coefficient of ethanol was estimated through the Einstein's formula for every χ_e case. We relate these results and attempt the molecular description of the dependency of the ethanol self-diffusion coefficient on the molar fraction of binary liquid.

Dynamics of different molecules adsorbed in porous media

We present in this paper a comparative study on the dynamics of benzene, cyclohexane, and methanol molecules, confined in the pores of MCM-41 molecular sieve and HZSM-5 zeolite. The quasi-elastic neutron scattering (QENS) measurements revealed that the physical state of these adsorbed molecules depended not only on the structural characteristics of the host matrix but also on the chemical properties, such as dipole moment, of the guest molecules. Thus, while no motion was observed in the time-scale of 10−10−10−12 s in the case of methanol, the larger size benzene and cyclohexane molecules are found to perform six-fold and three-fold jump rotation, respectively, when adsorbed inside the cages of HZSM-5 at room temperature. At the same time, all the three molecules are found to undergo a translational motion inside the pores of MCM-41 molecular sieves, the value of diffusion constant being the lowest in case of methanol because of its higher polarity. Translationl motion of the guest molecules inside the pores of MCM-41 can be satisfactorily described by Chudley-Eliott fixed jump length diffusion and accordingly the residence time, jump length and diffusion constant are estimated.

Epoxidation of cyclohexene catalyzed by manganese porphyrins: Ab initio DFT studies

The reaction of catalytic epoxidation of cyclohexene molecule over the manganese porphyrin has been studied by the DFT methods. Parallel and perpendicular mutual orientations of reacting species have been considered leading to eight different reaction paths, with the cyclohexene species approaching the catalyst oxo-group from above and from the side of the porphyrin plane (at three different heights). Three possible positions in which the cyclohexene molecule may physisorb on the catalyst have been found. Results of calculations indicate that the formation of the epoxide may occur when the cyclohexene molecule approaches the catalyst oxo-group from above in a parallel orientation.

Observation of Energy Transfer at D2O Ice/CO/Pt(111) Interface by Time-resolved SFG Spectroscopy

Dynamic behavior of cyclohexane adsorbed on Ni(111) under the irradiation of NIR pulses (1064 nm) was studied by time-resolved sum-frequency generation (SFG). Two types of adsorbed cyclohexane were observed on Ni(111), which were attributed to the ordered cyclohexane domains at high coverage and disordered cyclohexane molecules. When the surface was temporally heated up by the irradiation with the NIR pulses, the disordered cyclohexane molecules were thermally excited to form the ordered structure.

Following changes in the porous texture of Nomex-derived activated carbon fibres with the molecular probe technique

A series of Nomex-derived activated carbon fibres (ACFs) activated to different burn-offs (BOs) together with two series derived from the previous ACFs through chemical vapour deposition (CVD) treatments were used as adsorbents. The adsorption of molecules of different size, namely, dichloromethane, benzene, cyclohexane and carbon tetrachloride was used to monitor the textural evolution of microporous carbon fibres owing to these treatments. The analysis of the results showed that carbon deposit has taken place mainly at the entrance of the pores rather than in the interior. The information obtained about the porous structure and the molecular sieve behaviour of the samples in the different series was also useful for establishing the possible uses of these materials: thus, the obtained ACFs could be used for adsorbing volatile organic compounds (VOCs) in the field of environmental control while CVD-treated ACFs could be used as adsorbents for gas separations. In particular, the combined use of CH 2Cl 2 and C 6H 6 could be used to determine whether an adsorbent is a good carbon molecular sieve (CMS) for CO 2/CH 4 separation.

Inhomogeneous Distribution and Collective Diffusion of Solution Molecules in the Nanochannel of Mesoporous Silica

13C NMR spectra were observed for the mixed solutions composed of 2-propanol and cyclohexane in contact with a mesoporous silica, MCM-41, to study the distribution and dynamics of these molecules in the nanochannel of MCM-41. From the analysis of the spectral and relaxation data, we deduced that a high concentration gradient exists in the radial distribution of these liquid molecules in the nanochannel: alcohol molecules prefer the region near the surface and cyclohexane molecules the central portion of the nanochannel. Further evidence for this new model have been obtained by the spin-probe ESR observations. In addition, we obtained a model for the movement of solution molecules in the nanochannel: molecules “flow or diffuse collectively” by slipping on the channel surface.

The circular dichroism (CD) and absorption studies of 1,4,5,8-naphthalene tetracarboxydiimide dimer in terms of vibronic coupling theory

Abstract The vibronic dimer model is formulated in order to study the absorption and circular dichroism (CD) spectra of (1 R ,2 R )-1,2-bis-( N ′ -cyclohexyl-1 ′ ,4 ′ ,5 ′ ,8 ′ -naphthalenetetracarboxydiimido) cyclohexane (NTD) molecule treated as a dimer with the 1,4,5,8-naphthalenetetracarboxydiimide chromophores. To find out the most stable conformation of the NTD molecule the RHF/STO-3G and the density functional B3LYP/3-21G methods are employed. The results of conformational analysis are shown to be entirely consistent with the experiment. In particular it is shown that the CD and absorption spectra of the NTD dimer observed in the excitation region 25,000–35,000 cm −1 are correctly reproduced by the vibronic dimer model applied with the model parameters directly obtained from CASSCF/5π4n5π * computations. In the debatable region the CD of the NTD dimer results from the 1 1 A g →1 1 B 2 u and 1 1 A g →1 1 B 3 u overlapping transitions in the chromophore. Since that later transition is hidden in the vibronic manifold of the former, the effect of the hidden state on the chiroptical properties of the NTD molecule is discussed in some details.

Correlating Mechanical Strain with Low-Temperature Hydrogenation Activity on Submonolayer Ni/W(110) Surfaces

In the current paper we report a unique low-temperature hydrogenation pathway on submonolayer Ni/W(110) surfaces, which does not occur on either clean W(110) or on Ni/W(110) surfaces with Ni coverages greater than one monolayer (ML). Cyclohexene (c-C6H10) is used as a probe molecule to investigate the hydrogenation activity of Ni films deposited on a W(110) surface. Using Auger electron spectroscopy (AES), temperature-programmed desorption (TPD), low-energy electron diffraction (LEED), X-ray photoelectron spectroscopy (XPS), and high-resolution electron energy loss spectroscopy (HREELS), we have studied the reaction products and the bonding mechanisms of cyclohexene on various Ni/W(110) surfaces. On a clean W(110) surface, cyclohexene molecules undergo decomposition without producing the hydrogenation product, cyclohexane (c-C6H12). In contrast, a low-temperature (237 K) hydrogenation pathway is detected after the W(110) surface is covered with submonolayer coverages of Ni. The maximum hydrogenation activ...

Syntheses and Crystal Structures of Three-Dimensional Cyanocadmate Clathrates with Imidazole

The crystal structures of two clathrates with imidazole (=imH), [Cd3(CN)6(imH)2]·C6H12, I, and [Cd3(CN)6(imH)2]·C6H5Cl, II, have been analyzed by single-crystal X-ray diffraction methods. Clathrate I crystallizes in the monoclinic system, space group P21/n with a=13.416(2), b=14.140(2), c=14.151(1)Å, β=105.08(9)°, V=2592.1(5)Åsup3;, Z=4, R 1=0.0360, wR 2=0.0850 for 5931 independent reflections; II: monoclinic P21/n, a=12.369(2), b=14.313(2), c=14.416(4)Å, β=106.04(2)°, V=2452.7(9)Åsup3;, Z=4, R 1=0.0398, wR 2=0.1105 for 5642 independent reflections. The three-dimensional host structures of clathrates I and II are isostructural with each other. The host framework is built through cyanide bridges among two kinds of Cd ions, tetrahedral and octahedral, in a ratio of 2 : 1. The tetrahedral Cd(1) centre is linked to three octahedral Cd(3) atoms and one tetrahedral Cd(2) atom; the tetrahedral Cd(2) centre is ligated by one unidentate imidazole ligand and linked to one tetrahedral Cd(1) atom and two octahedral Cd(3) atoms; the octahedral Cd(3) centre is ligated by one unidentate imidazole ligand and linked to three tetrahedral Cd(1) atoms and two tetrahedral Cd(2) atoms. The novel host structure provides two types of channels, a large, elongated, rectangular channel and a small rectangular channel. The larger channel is occupied by imidazole ligands coordinated to tetrahedral Cd(2) and octahedral Cd(3). The smaller channel accommodates the guest molecules cyclohexane and chlorobenzene.

Effect of pore characteristics on the dynamics of cyclohexane molecules confined in ZSM-5 and MCM-41 molecular sieves: FTIR and QENS study

Fourier-transform infrared and quasi-elastic neutron scattering investigations have revealed that the cyclohexane molecules undergo phase transformation on adsorption at room temperature in HZSM-5 and MCM-41 molecular sieves. A comparison with similar studies on polycrystalline silica and zeolite-Y confirmed that the physical state of occluded molecules depended upon the size and the structure of the pores in host material. The confinement in HZSM-5 resulted in the development of non-equilibrium and highly condensed phase of cyclohexane, which remained trapped in the zeolitic pores even after partial desorption. This compression of cyclohexane as a result of adsorption in HZSM-5 is in agreement with the reported phenomena of super-cooling on physical confinement of fluids inside the narrow pores. On the other hand, relatively smaller amounts of cyclohexane were held in the pores of MCM-41 during the adsorption under identical conditions; and for all the loadings below 5 mmol g−1 the guest molecules acquired a transition state the density of which lay between that of the vapor and the liquid phases of cyclohexane. The results of this study are consistent with our recent findings on the formation of a clustered state of benzene during its adsorption into microporous materials (A. Sahasrabudhe, V. S. Kamble, A. K. Tripathi and N. M. Gupta, J. Phys. Chem. B, 2001, 105, 4374; A. K. Tripathi, A. Sahasrabudhe, S. Mitra, R. Mukhopadhyay, N. M. Gupta and V. B. Kartha, Phys. Chem. Chem. Phys., 2001, 3, 4449), and are also in line with the current theories on capillary condensation of fluids in narrow pores.

Permeation of binary mixtures of benzene and saturated C 4–C 7 hydrocarbons through an FAU-type zeolite membrane

The permeation and separation properties through an FAU-type zeolite membrane for mixtures of benzene and saturated C 4–C 7 hydrocarbons were investigated at a permeation temperature of 373 K. The data related to permeation were cited from previous papers, and the new data on adsorption were obtained for such binary mixtures with and without benzene. The high benzene/cyclohexane separation factor can be attributed to the high adsorption selectivity in favor of benzene and the blockage against cyclohexane. The proposed model is as follows: For the feed of single-component benzene or cyclohexane, the adsorption of benzene is higher than that of cyclohexane, while the diffusivity of benzene is lower than that of cyclohexane. As a result, permeance to cyclohexane is higher than that to benzene. For the case of the feed consisting of an equimolar mixture of benzene and cyclohexane, the adsorption of benzene is smaller than that for the case of a single-component feed. Meanwhile, cyclohexane molecules are expelled from the adsorption sites by benzene, and the benzene/cyclohexane selectivity for adsorption reaches a value of approximately 19. The benzene molecules which are moving toward the permeate side frequently block the windows, and the diffusivity of cyclohexane through the windows is greatly retarded. The small separation factors for mixtures of saturated C 6 hydrocarbons can be explained based on a single-file diffusion mechanism.

A combined MD-IQNS investigation of rotational disorder of guest molecules in thiourea inclusion compounds

In thiourea inclusion compounds the host substructure comprises a hydrogen-bonded arrangement of thiourea molecules and contains 1-D channels within which guest molecules are located. These organic composite crystals display structural phase transitions on cooling from room temperature. Our aim is to elucidate the mechanisms of the phase transitions in these materials. The dynamics of the guest molecules has been investigated by means of incoherent quasielastic neutron scattering spectroscopy and computer simulations have been performed to help in the interpretation of the experimental data. In this short note we report the preliminary analysis of the dynamics of cyclohexane and chlorocyclohexane guest molecules in the high-temperature phases of their inclusion compounds.