Cyclohexane Molecules Research Articles

Experimental determination of deviation from spherical electron densities of atoms in cyclohexane molecules in the liquid state

Abstract Deviation from the spherical electron distribution of atoms in liquid cyclohexane has been determined through the difference interference term between the observed x-ray intermolecular interference term and the sum of the intermolecular partial structure factors weighted by x-ray atomic scattering factors. The difference distribution function indicates a broadened negative peak at r ∼ 3.7 Å, suggesting that the electron density decreases in the radial distance that corresponds to the intermolecular distances of neighboring cyclohexane molecules.

Synergy of pore size and silanols in an –SVR-type zeolite for efficient dynamic benzene/cyclohexane separation

The efficient purification of cyclohexane is critical, serving as an essential feedstock to produce resins, nylon fibers and pharmaceutical intermediates. However, efficient purification remains a challenging task due to the similarity of cyclohexane and benzene molecules in terms of size and boiling point. In this work, we reported on the synergy of pore size and silanols inside an -SVR-type zeolite for the efficient production of ultrapure cyclohexane (benzene <1 ppm) from benzene/cyclohexane mixture. Under ambient conditions, the SSZ-74 zeolite demonstrated the highest mass-based productivity of 14.5 L/kg for ultrapure cyclohexane among several common zeolites with a considerable dynamic selectivity of ~9.5. The separation ability was evaluated through density functional theory (DFT) calculations and ab initio molecular dynamics (AIMD) simulations. The unique ordered silanols inside the zeolite frameworks demonstrated strong but reversible interactions with benzene through SiOH…π interactions, as revealed by in situ Fourier Transform infrared (FTIR) spectra.

Fick and Maxwell-Stefan diffusion of the liquid mixture cyclohexane + toluene + acetone + methanol and its subsystems

Transport diffusion of the quaternary mixture cyclohexane + toluene + acetone + methanol and most of its binary and ternary subsystems at ambient conditions of temperature and pressure is studied by molecular dynamics simulation. Liquid-liquid phase separation of cyclohexane + methanol extends into the according ternary and quaternary mixtures, rendering them highly non-ideal. Maxwell-Stefan diffusion and intradiffusion coefficients are predicted with the Green-Kubo formalism, while the thermodynamic factor is sampled with Kirkwood-Buff integration. From these data, the Fick diffusion coefficient is determined and thoroughly compared with experimental literature values. Given that the simulation results for all binaries, one of the ternaries and the quaternary mixture are successfully validated, it can be assumed that the results for the three remaining ternary mixtures, for which no experimental data exist, are sound, too. These three ternaries exhibit non-idealities that entail Maxwell-Stefan diffusion coefficient maxima that are accompanied by Fick diffusion coefficient minima due to the thermodynamic factor. Particularly the very different nature of cyclohexane and methanol molecules, where the latter strongly self-associate, leads to anomalies. The predictive models by Li et al. (2001) and Allie-Ebrahim et al. (2018) for binary and ternary mixtures, respectively, are found to yield good results for predicting the Fick diffusion coefficient of these challenging systems.

Graphene oxide aerogels for adsorptive separation of aromatic hydrocarbons and cycloalkanes

Efficient separation of benzene and cyclohexane has critical importance for production of commodity chemicals, and is one of the most challenging separations in the industry. Physisorption by recyclable, porous solids has a significant potential in substituting energy-intensive azeotropic or extractive distillation methods. Reduced graphene oxide aerogels (rGOAs) are emerging materials holding great promise for connecting unique properties of 2D graphene with ordinary 3D materials. The benzene/cyclohexane separation on rGOAs self-assembled by the chemical reduction with l-ascorbic acid, sodium bisulphite and (for the first time) sodium dithionite was studied by dynamic gas adsorption methods, and the adsorption performance was analysed in relation to aerogels physicochemical properties. The aerogel reduced with sodium dithionite (rGOA_DTN) had the highest reduction degree and specific surface area (461.2 m2g-1), with the highest contribution of mesopores. It was also the sample with the uppermost uptake of benzene and cyclohexane. The binary component adsorption on rGOA_DTN resulted in the selectivity of the adsorption of benzene over cyclohexane of 2.1. Adsorption-desorption studies demonstrated the excellent thermal stability of the adsorbent in the long-run operation. Because the adsorption capacity did not correlate with the mesopores but with macropores surface area, the selectivity of the adsorption was attributed to the different physicochemical structure of aerogels surface. The benzene molecule interacted strongly by specific C-H···π interactions, while the cyclohexane molecule was excluded from the surface of aerogels because of its shape/size. Results demonstrated that rGOAs can be a versatile and flexible platform for adsorptive gas-phase hydrocarbons separation.

Adsorption of cadmium selenide clusters: A novel approach to enhance solar energy conversion using armchair graphene nanoribbons

Tailoring the electronic, optical, and transport properties of low-dimensional semiconductor materials is essential to improve the light-conversion efficiency of thin-film solar cell materials. Here, using first-principles calculations and non-equilibrium Green functions, we investigate the enhancement of optoelectronic and transport properties of armchair graphene nanoribbons (AGNRs) upon adsorption of cadmium selenide clusters. Upon adsorption of a CdSe diatomic molecule on an AGNR, the most energetically favorable configuration is the cadmium end sitting on top of a carbon atom. The corresponding electronic bandgap reduces ∼5 times with respect to that of the pristine system, thanks to the formation of a polaron state formed by the p-orbital of the selenide atom. Upon adsorption of CdSe cyclohexane molecules, the bandgap of this system slightly shrinks by 0.121 eV with respect to the pristine system. The charge accumulation induced by these clusters significantly enhances the absorption coefficient of the adsorbed systems, resulting in a red shift of the optical spectra toward the infrared region. More interestingly, by solving the Bethe–Salpeter equations with the Tamm–Dancoff approximation, we provide a direct link between the first-principles optical prediction and experimental observations. In addition, the electron transfer from these molecules to the hosted systems increases the transmission spectra in the vicinity of the Fermi level, leading to a remarkable electronic current passing through these scattering regions. These results highlight the role of cadmium selenide clusters in enhancing the light-to-energy conversion efficiency of next-generation solar cell devices.

Shear-activation of mechanochemical reactions through molecular deformation.

Mechanical stress can directly activate chemical reactions by reducing the reaction energy barrier. A possible mechanism of suchmechanochemical activation is structural deformation of the reactant species. However, the effect of deformation on the reaction energetics is unclear, especially, for shear stress-driven reactions. Here, we investigated shear stress-driven oligomerization reactions of cyclohexene on silica using a combination of reactive molecular dynamics simulations and ball-on-flat tribometer experiments. Both simulations and experiments captured an exponential increase in reaction yield with shear stress. Elemental analysis of ball-on-flat reaction products revealed the presence of oxygen in the polymers, a trend corroborated by the simulations, highlighting the critical role of surface oxygen atoms in oligomerization reactions. Structural analysis of the reacting molecules in simulations indicated the reactants were deformed just before a reaction occurred. Quantitative evidence of shear-induced deformation was established by comparing bond lengths in cyclohexene molecules in equilibrium and prior to reactions. Nudged elastic band calculations showed that the deformation had a small effect on the transition state energy but notably increased the reactant state energy, ultimately leading to a reduction in the energy barrier. Finally, a quantitative relationship was developed between molecular deformation and energy barrier reduction by mechanical stress.

Guest Uptake and Exchange in One‐Dimensional Channels of Metal‐Organic‐Framework Films

AbstractThe mass transfer in a film of metal‐organic framework with one‐dimensional pores, oriented perpendicular to the substrate surface, was gravimetrically explored. The diffusion coefficients of the probe molecules cyclohexane and p‐xylene were determined from the transient uptake curves. When exchanging cyclohexane by p‐xylene in the MOF pores, the mass transfer was significantly slower than the plain, single‐component uptakes. However, a single‐file‐diffusion situation, where mutual passage is hindered, tremendously slowing down the mass transfer, was not found.

Effect of Cyclohexane on the Combustion Characteristics of Multi-Component Gasoline Surrogate Fuels.

It has been discovered that there is a dynamic coupling between cycloalkanes and aromatics, which affects the number and types of radicals, thereby controlling the ignition and combustion of fuels. Therefore, it is necessary to analyze the effects of cyclohexane production in multicomponent gasoline surrogate fuels containing cyclohexane. In this study, a five-component gasoline surrogate fuel kinetic model containing cyclohexane was first verified. Then, the effect of cyclohexane addition on the ignition and combustion performance of the surrogate fuel was analyzed. This study shows that the five-component model exhibits good predictive performance for some real gasoline. Meanwhile, the addition of cyclohexane decreases the ignition-delay time of the fuel in the low and high temperature bands, which is caused by the early oxidation and decomposition of cyclohexane molecules, generating more OH radicals; in the medium temperature band, the isomerization and decomposition reactions of cyclohexane oxide cC6H12O2 dominate the temperature sensitivity of the ignition delay, affecting the small molecule reactions that promote the generation of reactive radicals such as OH, thus inhibiting the negative temperature coefficient behavior of the surrogate fuel. The laminar flame speed of the surrogate fuels increased with the increase in the proportion of cyclohexane. This is due to the fact that the laminar flame speed of cyclohexane is higher than that of chain and aromatic hydrocarbons, and the addition of cyclohexane dilutes the ratio of chain and aromatic hydrocarbons in the mixture. In addition, engine simulation studies have shown that at higher engine speeds, the five-component surrogate fuel containing cyclohexane requires lower intake-gas temperatures to achieve positive ignition and are closer to the in-cylinder ignition of real gasoline.

Determining the Height of Energy Barriers of the Cyclohexene Molecule Using Stochastic Approximation

The Monte Carlo method (stochastic approximation) is used for calculating the relative values of density of the states of the cyclohexene molecule in the space of Cremer–Pople coordinates. Using this data, the heights of the energy barriers separating the molecule stereoisomers are estimated.

Determining the Height of Energy Barriers of the Cyclohexene Molecule Using Stochastic Approximation

Determining the Height of Energy Barriers of the Cyclohexene Molecule Using Stochastic Approximation

Cyclo-hexane plastic phase I: single-crystal diffraction images and new structural model.

The plastic phase of cyclohexane (polymorph I) was studied by Kahn and co-workers, without achieving a satisfactory determination of the atomic coord-inates [Kahn et al. (1973). Acta Cryst. B29, 131-138]. The positions of the C atoms cannot be determined directly as a consequence of the disorder in a high-symmetry space group, an inherent feature of plastic materials. Given this situation, the building of a polyhedron describing the disorder was the main tool for determining the molecular structure in the present work. Based on the shape of reflections {111}, {200} and {113} in space group Fm 3 m, we assumed that cyclohexane is disordered through the action of rotation group 432. The polyhedral cluster of disordered molecules is then a rhombic dodecahedron centred on the nodes of an fcc Bravais lattice. The vertices of this polyhedron are the positions of C atoms for the cyclohexane molecule, which is disordered over 24 positions. With such a model, the asymmetric unit is reduced to two C atoms placed on special positions, and an acceptable fit between the observed and calculated structure factors is obtained.

Control of the pore chemistry in metal-organic frameworks for efficient adsorption of benzene and separation of benzene/cyclohexane

Control of the pore chemistry in metal-organic frameworks for efficient adsorption of benzene and separation of benzene/cyclohexane

APPLICATIONS OF NMR AND THEORETICAL CALCULATIONS TO STUDY THE O-H∙∙∙N INTRAMOLECULAR HYDROGEN BOND EFFECT ON THE CONFORMATIONAL EQUILIBRIUM OF CIS-3-N-ETHYLAMINOCYCLOHEXANOL AND CIS-3-N,N-DIETHYLAMINOCYCLOHEXANOL

Textbooks show that in cis-1,3-disubstituted cyclohexane molecule, the conformer with the substituents in the diaxial positions is higher in energy and hence, it presents a low population in the conformational equilibrium. The diaxial conformer is destabilized by the repulsion between the substituent groups and the axial hydrogen atoms on the same side of the ring. This interaction is known as the 1,3-diaxial interaction. In this study, the solvent effect on the conformational equilibria of cis-3-N-ethylaminocyclohexanol (cis-3-EACOL) and cis-3-N,N-diethylaminocyclohexanol (cis-3-DEACOL) has been assessed through the spin-spin coupling constant (3JHH). The results show that the diaxial conformation of cis-3-EACOL decreases from 92% in CCl4 (∆Gee-aa = 1.48 kcal mol-1 ) to 10% in DMSO-d6 (∆Gee-aa = −1.31 kcal mol-1). For cis-3-DEACOL the diaxial conformer decreased from 36% in CCl4 (∆Gee-aa = −0.33 kcal mol-1) to 7% in Pyridine-d5 (∆Gee-aa = −1.55 kcal mol-1). The stabilization of the diaxial conformer in nonpolar solvents takes place due to the O-H···N intramolecular hydrogen bond, which overcomes the 1,3-diaxial steric interactions.

Selective adsorption to benzene-cyclohexane gas-phase mixture over ion exchange Y zeolites

The selective adsorption to benzene-cyclohexane gas-phase mixture was performed over several parent zeolites (NaY, NaZSM-5, and NaMOR) and over ion exchanged Y zeolites. NaY showed a greatly higher adsorption selectivity & capacity to benzene than NaZSM-5 and NaMOR, primarily attributed to the high density of surface Na+ sites, the high specific surface area, and the better pore diffusion ability of the former. Moreover, a reasonable Zn2+ ion exchange treatment not only significantly enhanced the adsorption selectivity to benzene but also improved the benzene adsorption capacity of Y zeolite. This may be due to the uneven surface charge on the surface of Zn2+ exchanged Y zeolite, where the electrostatic attraction effect between surface Zn2+ and benzene molecules may powerfully promote the preferential adsorption to benzene which even replaces surface cyclohexane molecules. While the exchanged Y zeolites with Cu2+, Cr3+ or Fe3+ displayed the declined performance for selective adsorption. Especially, severe pore blockage occurred after Cr3+ or Fe3+ exchange. Furthermore, based on the optimization on the aspects of the solution concentration and the exchange time during Zn2+ ion exchange treatment, the selectivity to benzene of 93% & 98% and the benzene adsorption capacity of >3.0 mmol/g were obtained over 0.2-Zn-Y (2 h) and 0.1-Zn-Y (4 h) samples, respectively.

Singlet fission initiating triplet generations of BODIPY derivatives through pi -stacking: a theoretical study

The role of singlet fission (SF) in the triplet-state generation mechanism of 1,3,5,7-tetramethyl-boron-dipyrromethene derivatives is revealed by exploring the cause for the solvent dependence of the generation rate. Comparing the adsorption energy calculations of solvent molecules, i.e., cyclohexane, chloroform and acetonitrile molecules, to the derivatives with the pi -stacking energies of these derivatives surprisingly show that the hierarchy of the solvation energies and pi -stacking energies strongly correlates with the experimentally-suggested solvent dependence of the triplet-state generation of these derivatives for five and more adsorbing solvent molecules. Following this finding, the excitation spectra of these derivatives in acetonitrile solvent are explored using the proprietary spin-flip long-range corrected time-dependent density functional theory. It is, consequently, confirmed that the pi -stacking activates the second lowest singlet excitation to trigger the spin-allowed transition to the singlet doubly-excited tetraradical (TT)_1 state, which generates the long-lived quintet (TT)_1 state causing the SF. However, it is also found that the pi -stacking also get a slow intersystem crossing active around the intersections of the lowest singlet excitations with the lowest triplet T_1 excitations in parallel with the SF due to the charge transfer characters of the lowest singlet excitations. These results suggest that SF initiates the triplet-state generations through near-degenerate low-lying singlet and (TT) excitations with a considerable singlet-triplet energy gap after the pi -stacking of chromophores stronger than but not far from the solvation. Since these derivatives are organic photosensitizers, this study proposes that SF should be taken into consideration in developing novel heavy atom-free organic photosensitizers, which will contribute to a variety of research fields such as medical care, photobiology, energy science, and synthetic chemistry.

The nature of “hydrogen spillover”: Site proximity effects and gaseous intermediates in hydrogenation reactions mediated by inhibitor-scavenging mechanisms

Support effects in alkene and arene hydrogenations on metal catalysts attributed to “hydrogen spillover” are shown to reflect the desorption and hydrogenation of Pt-bound intermediates at acid-base pairs on certain oxides (e.g. Al2O3, TiO2, MgO). Toluene-H2 reactions on Pt nanoparticles dispersed on SiO2 (Pt/SiO2) occur on surfaces nearly saturated with a diverse pool of bound species differing in the locations of H-atoms and surface attachments. Their diverse coverages and reactivity cause Pt surfaces to become preferentially occupied by less reactive isomers at the expense of the more competent isomers that account for most hydrogenation turnovers. These less reactive species can desorb from Pt nanoparticles as gaseous methylcyclohexadiene molecules, which diffuse to and react at nearby oxide surfaces; such scavenging increases the relative abundance of the more reactive intermediates at Pt surfaces leading to the rate enhancements inaccurately denoted as “hydrogen spillover.” These rate enhancements become less pronounced as mean inter-function distances between Pt nanoparticles and acid-base pairs on oxide surfaces increase, and as methylcyclohexadiene molecules become less effectively scavenged as their rates of mass transfer become consequential. The Al2O3 surfaces considered here catalyze dihydrogen addition to cyclohexadiene and cyclohexene molecules (but not toluene); titration of acid-base pairs by propanoic acid suppresses such reactions, as well as the significant enhancements of toluene-H2 reaction rates observed when Al2O3 is mixed physically with Pt/SiO2. The rate enhancements conferred by these bifunctional routes represent a natural consequence of the diverse coverage and reactivity of many different species bound on crowded metal surfaces during arene and alkene hydrogenation reactions. Their desorption as partially-hydrogenated molecules enable their scavenging at a second function present within diffusion distances, without requiring inter-function contact or the surface diffusion of H atoms.

Equilibrium Solubility of Triclocarban in (Cyclohexane + 1,4-Dioxane) Mixtures: Determination, Correlation, Thermodynamics and Preferential Solvation

Equilibrium solubility of triclocarban (TCC) expressed in mole fraction in 1,4-dioxane and cyclohexane, as well, as in 19 {cyclohexane (1) + 1,4-dioxane (2)} mixtures, was determined at seven temperatures from T = (288.15 to 318.15) K. Logarithmic TCC solubility in these cosolvent mixtures was adequately correlated with a lineal bivariate equation as function of both the mixtures composition and temperature. Apparent thermodynamic quantities for the dissolution and mixing processes were computed by means of the van’t Hoff and Gibbs equations observing endothermal and entropy-driven dissolution processes in all cases. The enthalpy–entropy compensation plot of apparent enthalpy vs. apparent Gibbs energy was linear exhibiting positive slope implying enthalpy-driving for TCC transfer from cyclohexane to 1,4-dioxane. Ultimately, by using the inverse Kirkwood–Buff integrals it is observed that TCC is preferentially solvated by cyclohexane molecules in 1,4-dioxane-rich mixtures but preferentially solvated by 1,4-dioxane molecules in cyclohexane-rich mixtures.

Cyclohexane and n-hexane adsorption studies on novel hex-star antimonene nanosheets – A first-principles outlook

• The geometrically stable hex-star antimonene nanosheets possesses an energy band gap of 0.862 eV. • Cyclohexane and n-hexane molecules are adsorbed on hex-star antimonene nanosheet. • Both cyclohexane and n-hexane are physisorbed on hex-star antimonene. • Hex-star antimonene nanosheets exhibits chemi-resistive nature upon adsorption of cyclohexane and n-hexane. The presence of acetic acid, nitrates, vat dyes, and heavy metals all collectively produce highly toxic effluent from the textile industry. The aliphatic hydrocarbons, namely cyclohexane, and n-hexane are the common toxic volatiles emitted from the various textile industry in worldwide leading to environmental degradation and human illnesses. Hence, there is a requirement for high sensitivity and a stable chemical sensor for detecting these toxic molecules to safeguard human health and the air atmosphere. In this research, we used hex-star antimonene as a leading sensing material to detect cyclohexane and n-hexane molecules at ambient temperature. Originally, the structural firmness of hex-star antimonene is validated with the influence of cohesive formation energy. Furthermore, the band structure and projected density of states spectrum provides the fingerprint for electronic properties of hex-star antimonene. The band gap of hex-star antimonene is calculated to be 0.862 eV. Significantly, the adsorption properties of cyclohexane and n-hexane on the base substrate are investigated by the deciding factors, such as Bader charge transfer, adsorption energy, and relative band gap variations. The scope of adsorption energy (−0.115 eV to −0.502 eV) confirms that both cyclohexane and n-hexane are physisorbed on hex-star antimonene. The outcome recommended that hex-star antimonene can be utilised as a chemical sensor to monitor the cyclohexane and n-hexane emitted from textile industries.

Water to cyclohexane transfer free energy calculations for a carbon nanotube

We calculate the difference in the solvation free energy of a carbon nanotube in water and cyclohexane and introduce two methods to perform these calculations. One is to use thermodynamic integration and gradually decouple the interactions of the nanotube with these solvents. The other is to build a water–cyclohexane system and create a transition path for the nanotube on a direction normal to the water–cyclohexane interface, and employ umbrella sampling simulations on the path and calculate the free energy difference between the states. By combining the solvation free energies of the nanotube computed by thermodynamic integration, we infer correlations with the free energies of transfering the nanotube directly from the one solvent to the other, computed by umbrella simulations. The correlations depend on how many molecules of the one solvent partition into the other together with the nanotube. We measure this amount by averaging the water accessible surface area of the nanotube over the umbrella sampling simulations. When the direction is from cyclohexane to water, cyclohexane molecules are coextracted with the nanotube into the water phase. These molecules remain adsorbed inside the pore, even when the nanotube enters adequately the aqueous solution. The adsorbed phase of cyclohexane configures an almost complete monolayer over the internal surface of the nanotube making it inaccessible to water.

The separation performance of two-dimensional ZnPP-grid molecular sieve for C6 alkane molecules:A first-principles calculation

Membrane separation technology plays a vital role in producing high-octane gasoline field. Based on the first-principles calculation, ZnPP-Grid molecular sieve with uniform intrinsic pore is used to systematically evaluate the separation performance of hexane isomers and cyclohexane. The difference of energy barriers indicates that ZnPP-Grid membrane allows linear hexane molecule to pass through the pore, but block di-branched 2,2-dimethylbutane molecule. The analysis of geometric and energy variation reveals that during penetration processes, the effect of molecular changes on the penetration barrier is greater than the effect of ZnPP-Grid membrane deformation on barrier, which is related to the size and structural flexibility of molecules and ZnPP-Grid molecular pore. Especially, when cyclic cyclohexane molecule travels to the pore area, the maximum geometric distortion of pore-rimmed atoms have not caused higher energy barrier than mono-branched 3-methylpentane, which also proves the flexibility of ZnPP-Grid membrane. The molecular sieve exhibits superior hexane/cyclohexane, hexane/branched isomers separation performance with high selectivity of 108–1080 within 150 K–400 K. More importantly, the hexane isomers mono-branched 3-methylpentane/di-branched 2,2-dimethylbutane can be discriminated with high selectivity ∼1029 at 300 K, which helps to obtain high-octane gasoline. The results demonstrate that the ZnPP-Grid molecular sieve is probably an excellent molecular sieve in petrochemical industry.