Improper hydrogen-bonded cyclohexane C-Hax?Yax contacts: experimental evidence from H NMR spectroscopy of suitable axial cyclohexane models

B3LYP/6-31+G(d,p) calculations predicted the presence of improper hydrogen-bonded C-H_ax?Y_ax contacts of different strength in cyclohexane derivatives;¹ it was predicted that the addition of an appropriate bridging fragment X_ax between an axial substituent Y₁ and a cyclohexane carbon would strengthen the improper hydrogen-bonded contact C-H_ax?Y₁ when the X_ax-Y₁ bond vector bisects the cyclohexane ring. To support the theoretical predictions with experimental evidence for this effect, several 2-substituted adamantane analogues with suitable improper H-bonded C-H_ax?O contacts of different strength were synthesized, as models of the corresponding cyclohexane derivatives, and their ¹H NMR spectra were recorded at 298 K. The ¹H NMR signal separation within the cyclohexane ring γ-CH₂s is increased when the B3LYP/6-31+G(d,p)-calculated strength of the H-bonded C-H_ax?O=C_ax contact interaction is increased.     

Substituent effects on chloro meso-tetra-ortho-alkylphenylporphinato iron catalyzed biomimetic oxidation of cyclohexane

Six sterically hindered chloro meso-tetra-ortho-alkylphenylporphinato irons (T(o-R)PPFe(HI)Cl, R = Me, Et, n-Pr, i-Pr, n-Bu, t-Bu) were synthesized and used to catalyze the monooxygenation of cyclohexane with PhIO. Both the yields of cyclohexanol and the relative rates of monooxygenation of cyclohexane catalyzed by T(o-R)PPFe(III)Cl were higher than those of TPPFe(III)Cl respectively. The order of the yields(%) of cyclohexanol and the rate of cyclohexanol formation in the monooxygenation of cyclohexane catalyzed by T(o-R)PPFe(III)Cl for the different substituents are: i-Pr(58) > Et(57) > n-Pr(52) > Me(51) > n-Bu(48) > t-Bu(46) > H(35) and i-Pr > Et > t-Bu > n-Pr > Me > n-Bu > H respectively. The special steric effect on the catalytic character of these different alkyl substituents in T(o-R )PPFe(III)Cl is proposed on the basis of the results.     

Solubilities of isobutane in methanol + benzene,methanol + cyclohexane and benzene + cyclohexane mixed solvent solutions at 298 K and 40–102 kPa

The solubilities of isobutane at pressures from 40 to 102 kPa and a temperature of 298.15 K are presented for three mixed solvent solutions: methanol + benzene, methanol + cyclohexane, and benzene + cyclohexane.     

Mechanism of dehydrogenation of cyclohexane on the crystalline α-oxide of chromium

Russian Chemical Bulletin - Dehydrogenation of cyclohexane on crystalline α-Cr2O3 proceeds according to a sextet-type mechanism. This conclusion agrees with the structural principles of...     

Transformations of ortho-quinones in the γ-radiolysis of their solutions in cyclohexane

The transformations of 4-tert-butyl-1,2-benzoquinone (I), 3,5-di-tert-butyl-1,2-benzoquinone (II), and 4-methoxy-5-tert-butyl-1,2-benzoquinone (III) in deaerated cyclohexane solutions under exposure to γ-radiation were studied. It was found by chromatography-mass spectrometry and ¹H and ¹³C NMR spectroscopy that the addition of cyclohexyl radicals at the C=O bond in compounds I–III resulted in monoalkyl ethers, whereas cyclic ketal XXI was also formed in the case of compound II. Moreover, quinone I afforded mixed O-and C-alkylation products, and the adduct of cyclohexyl radicals and quinone II at the C=C bond was the source of dimeric products.     

Adsorbents for acetone in cyclohexane effuent employed in Ziegler-Natta catalyst process

Adsorption of acetone from cyclohexane on silica, alumina, coal, natural and leached chrysotile was investigated. Adsorption phenomenon was investigated by non-linear fitting, considering the Langmuir or Freundlich models. According to non-linear regression, coal present the highest K _L (12.07) and K _F (9.115) parameters. Silica and leached chrysotile exhibited similar behavior in terms of both K _L and K _F parameters. Alumina presented the highest adsorption capacity according to both Langmuir (q _m =58.689) and Freundlich (1/n=0.844) models. Non-supported Ziegler-Natta catalyst systems were shown to be more sensitive to acetone contamination. For the polymerization reactions carried on with contaminated solvent after the percolation through the adsorbents, good results were observed in the case of silica and alumina. Coal was not suitable for use in this catalyst system, probably due to leaching of organic components by the solvent (cyclohexane).     

Separation of benzene/cyclohexane mixtures using polyurethane–silica hybrid membranes

Mixed sols were prepared by dissolving polyurethane (a 30 wt% solution in n-propanol, PU) and tetraethylorthosilicate (TEOS) in ethanol at PU:TEOS mass ratios of 1:2, 1:1, 2:1 and 3:1. Each of the sols was coated on a porous α-alumina support tube by the dipping method, and green membranes were heat-treated at 200°C for 1 h in an atmosphere of nitrogen. A PU membrane was also prepared with PU alone. The membranes were 5–6 μm thick. The polyurethane–silica membranes were swollen in benzene but only slightly in cyclohexane at room temperature. The degree of swelling in benzene decreased with increasing fractions of TEOS in the hybrid sols. The selectivity of benzene to cyclohexane was improved due to the suppression of swelling as a result of hybridization with TEOS. The total permeation flux and benzene/cyclohexane selectivity in the membrane prepared with a sol of PU:TEOS=1:1 were 3×10⁻⁵ kg m⁻² s⁻¹ and 19, respectively.     

Blind prediction of cyclohexane–water distribution coefficients from the SAMPL5 challenge

In the recent SAMPL5 challenge, participants submitted predictions for cyclohexane/water distribution coefficients for a set of 53 small molecules. Distribution coefficients (log D) replace the hydration free energies that were a central part of the past five SAMPL challenges. A wide variety of computational methods were represented by the 76 submissions from 18 participating groups. Here, we analyze submissions by a variety of error metrics and provide details for a number of reference calculations we performed. As in the SAMPL4 challenge, we assessed the ability of participants to evaluate not just their statistical uncertainty, but their model uncertainty—how well they can predict the magnitude of their model or force field error for specific predictions. Unfortunately, this remains an area where prediction and analysis need improvement. In SAMPL4 the top performing submissions achieved a root-mean-squared error (RMSE) around 1.5 kcal/mol. If we anticipate accuracy in log D predictions to be similar to the hydration free energy predictions in SAMPL4, the expected error here would be around 1.54 log units. Only a few submissions had an RMSE below 2.5 log units in their predicted log D values. However, distribution coefficients introduced complexities not present in past SAMPL challenges, including tautomer enumeration, that are likely to be important in predicting biomolecular properties of interest to drug discovery, therefore some decrease in accuracy would be expected. Overall, the SAMPL5 distribution coefficient challenge provided great insight into the importance of modeling a variety of physical effects. We believe these types of measurements will be a promising source of data for future blind challenges, especially in view of the relatively straightforward nature of the experiments and the level of insight provided.     

Solvation model for acetic acid in binary mixtures of cyclohexane–1,2-dichloroethane

The partition of acetic acid between aqueous solutions and various binary mixtures of 1,2-dichloroethane and cyclohexane were studied at 30.0 °C. The observed nonlinearities of both monomer partition coefficient and dimerization constant in the organic phase with the mole fraction of 1,2-dichloroethane are interpreted in terms of the preferential solvation of various solvation sites of the involved species. Two polar sites were identified for the monomer each with a solvation preference by 1,2-dichloroethane seven times that by cyclohexane. This preference decreases to about two upon dimerization.     

Fluid phase topology of ethanol+benzene+cyclohexane at 101.3 kPa

In this article, isobaric vapor–liquid equilibria for the ternary mixture of ethanol?+?benzene?+?cyclohexane was experimentally investigated at atmospheric pressure. Vapor–liquid equilibria data for ethanol?+?benzene?+?cyclohexane at 101.3?kPa were obtained with a Othmer-type ebulliometer. Data were tested and considered thermodynamically consistent. The experimental results showed that this ternary mixture is completely miscible and exhibits three binary homogeneous azeotropes and a ternary minimum azeotrope at the studied conditions. Satisfactory results were obtained for correlation of equilibrium compositions with UNIQUAC activity coefficients model and also for prediction with UNIFAC method. In both cases, low root mean square deviations of vapor mole fraction and temperature were calculated. The capability of ethanol as modified distillation agent at atmospheric condition is discussed in terms of the thermodynamic topological analysis. However, owing to the complex topology of the ternary mixture it leads to a distillation scheme with three columns and difficult operation and thus, ethanol is not recommended as a separating agent for benzene?+?cyclohexane azeotrope.     

Why Doesn't all-trans-1,2,3,4,5,6-Hexaspiro(THF)cyclohexane complex metal ions?

Despite the inherent preference for placing alkyl substituents, rather than alkoxy substituents, in equatorial positions, all-trans-hexaspiro(THF)cyclohexane strongly favors the all-O-equatorial conformer. Ab initio and density functional calculations on a series of cyclohexane derivatives containing one, two, or three spiro(THF) units demonstrate that this preference results from at least two important factors. First, when oxygen atoms are attached to adjacent carbons, the gauche effect favors the di-O-equatorial arrangement. In trans-1,2-dispiro(THF)cyclohexane, the single gauche interaction overcomes the inherent steric preference for projecting the two oxygen atoms axially. Similarly, in the all-trans-hexaspiro(THF)cyclohexane the six gauche interactions in the all-O-equatorial conformer overpower the inherent conformational biases of the six isolated spiro(THF) moieties. Nevertheless, the gauche effect only partially accounts for the more than 20 kcal/mol conformational bias calculated for this molecule. There is also another factor, the high energetic cost associated with projecting multiple alkoxy substituents axially on the same face of a cyclohexane scaffold. The calculations find the energetic cost of each 1,3-diaxial interaction is about 2 kcal/mol larger between alkoxy substituents than between alkyl substituents.     

Preparation of Co- or Mn-substituted LTL zeolites and their catalytic properties in cyclohexane oxidation

Co-or Mn-substituted LTL zeolites were hydrothermally synthesized by a novel organic-ligand-assisted method.XRD,UVVis DRS,XPS,and EPR techniques verified that the Co and Mn ions were incorporated into the zeolite framework.No organic species were retained in as-synthesized Co or Mn-LTL zeolites,which resulted in porous materials without calcination.In the oxidation of cyclohexane with tert-butyl hydroperoxide(TBHP),the Co-LTL and Mn-LTL gave a 40%–48%KA oil(cyclohexanone and cyclohexanol)yield as well as nearly 100%TBHP conversion under mild reaction conditions.The reactions were confirmed to be heterogeneous and to have proceeded catalytically.No loss of catalytic activity or leaching of metal active sites ions were observed during 4 reuses.     

Room temperature phosphorescence of α-bromonaphthalene induced by β-cyclodextrin in the presence of cyclohexane

β-Cyclodextrin (β-CD) can induce a-bromonaphthalene (BrN) to emit strong room temperature phosphorescence (RTP) in the presence of micro amounts of cyclohexane (c-hexane). Experiments of luminescence spectra, phosphorescence lifetime and fluorescence polarization prove the formation of c-hexane/β-CD/BrN ternary inclusion complex. The apparent formation constant of the ternary inclusion complex was determined and the effect mechanism of c-hexane on the RTP of BrN induced by β-CD is discussed.     

Reaction of 2-Alkoxypropenals with α-Hydroxyamino Oximes and 1,2-Bis(hydroxyamino)cyclohexane

Reactions of 2-alkoxypropenals with α-hydroxyamino oximes in neutral medium involve the aldehyde group of the former to afford both acyclic and cyclic azomethine oxides: N-(2-hydroxyiminoalkyl)-N-(2-alkoxy-2-propenylidene)amine oxides and 1-hydroxy-2,5-dihydroimidazole 3-oxides. The state of tautomeric equilibrium between the cyclic and acyclic products depends on the solvent nature and temperature. The reaction in acidic aqueous medium is accompanied by hydrolysis of the vinyl ether moiety in 2-alkoxy-propenals with formation of 2-oxopropionaldehyde which reacts with α-hydroxyamino oxime at the hydroxy-amino group to give substituted pyrazine 1,4-dioxides. The reaction of 2-alkoxypropenals with 1,2-bis-(hydroxyamino)cyclohexane leads to formation of 2-(1-alkoxyvinyl)-1,3-dihydroxyperhydrobenzimidazoles. The structure of the products was proved by IR, UV, and ¹H and ¹³C NMR spectroscopy and X-ray analysis.     

A novel approach for one-step forming ε-caprolactam from cyclohexane nitrozation catalyzed by transition metal salt

The nitrozation reaction of cyclohexane in one-step reaction to form ε-caprolactam has been studied using transition metal salt as catalysts in this work. The results indicated that the catalysts play an especially important role. This method is expected to be a novel way to synthesize other lactam by similar reaction. The possible mechanism was suggested.     

Spectral and kinetic characteristics of the α-propionic acid methyl ester radical in cyclohexane and water

The -propionic acid methyl ester radical was produced in dissociative electron capture reaction of 2-chloropropionic acid methyl ester. The absorption maxima of the radical are at 310 and 300 nm in cyclohexane and water with extinction coefficients of 440±50 and 400±50 mol^–1 dm³ cm^–1. The second order decay rate parameter in water is (2.3±0.5)×10⁹ mol^–1 dm³ s^–1. The peroxy radicals have the characteristics: _max=265–270 nm, _max=700–900 mol^–1 dm³ and 2k=(7±2)·10⁸ mol^–1 dm³ s^–1.     

Copper(II)-catalyzed CH oxidation of alkylbenzenes and cyclohexane with hydrogen peroxide

Copper(II) complex 1 efficiently catalyses the oxidation of alkylbenzenes and cyclohexane into the corresponding ketones in moderate to high yields in the presence of 30% H₂O₂. This protocol is simple, clean and generates water as the only by-product.     

Chiral differentiation of some cyclopentane and cyclohexane β-amino acid enantiomers through ion/molecule reactions

Chiral differentiation of four enantiomeric pairs of β-amino acids, cis-(1R,2S)-, cis-(1S,2R)-, trans-(1R,2R)-, and trans-(1S,2S)-2-aminocyclopentanecarboxylic acids (cyclopentane β-amino acids), and cis-(1R,2S)-, cis-(1S,2R)-, trans-(1R,2R)-, and trans-(1S,2S)-2-aminocyclohexanecarboxylic acids (cyclohexane β-amino acids) was performed successfully by using host-guest complexes and ion/molecule reactions. The experiments were conducted by using electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry. The effect of a chiral host molecule was tested by using three different host compounds; (+)-(18-Crown-6)-2,3,11,12-tetracarboxylic acid, (−)-(18-Crown-6)-2,3,11,12-tetracarboxylic acid, and β-cyclodextrin. This is the first time that small enantiomeric pairs with two chiral centers have been differentiated using ion/molecule reactions and host-guest complexes.